Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P0300, P0301, P0302, P0303, P0304
DTC P0300 : Random Misfire Detected DTC P0301 : No. 1 Cylinder Misfire Detected DTC P0302 : No. 2 Cylinder Misfire Detected DTC P0303 : No. 3 Cylinder Misfire Detected DTC P0304 : No. 4 Cylinder Misfire Detected
NOTE:
- Before you troubleshoot, review the general troubleshooting information .
- If the misfire is frequent enough to trigger detection of increased emissions during two consecutive driving cycles, the MIL will come on, and DTC P0300 (and some combination of P0301 through P0304) will be stored.
- If the misfire is frequent enough to damage the catalyst, the MIL will flash whenever the misfire occurs, and DTC P0300 (and some combination of P0301 through P0304) will be stored. When the misfire stops, the MIL will remain on.
- Troubleshoot the following DTCs first, if any of them were stored along with the random misfire DTC (s) (Because parts can sometimes fail without setting DTC's you should also do a physical inspection of the systems listed below):
P0087, P0088: Fuel rail pressure sensor
P0101, P0102, P0103: MAF sensor
P0106, P0107, P0108: MAP sensor
P0171, P0172: Fuel system
P0335, P0339: CKP sensor
P0340, P0344: CMP sensor A
P0351, P0352, P0353, P0354: No. 1-No. 4 cylinder ignition coil (s)
P0400, P0401, P0404, P0406, P2413: EGR system
P0506, P0507: Idle control system
P2648, P2649: VTEC system
| DTC Description | Confirmed DTC | Pending DTC | Freeze Frame |
|---|---|---|---|
| P0300 Random Misfire Detected | |||
| P0301 No. 1 Cylinder Misfire Detected | |||
| P0302 No. 2 Cylinder Misfire Detected | |||
| P0303 No. 3 Cylinder Misfire Detected | |||
| P0304 No. 4 Cylinder Misfire Detected |
DTC (PGM-FI)
- Problem verification - Idle
-1. Record the FREEZE DATA and the ONBOARD SNAPSHOT with the HDS.
-2. Start the engine, and let it idle.
-3. Monitor these parameters in the DATA LIST:
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Are the misfire counts increasing on any cylinder at idle?
YES
The engine is misfiring at idle, go to step 2.
NO
The engine does not misfire at idle, go to step 3.
- Determine Affected Cylinders
-1. Continue to monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Are the misfire counts generally isolated to a single cylinder?
-
YES
The misfire is isolated to a single cylinder.
- If the misfire counts are increasing every engine revolution (completely inactive cylinder), go to Single Cylinder Continuous Misfire at Idle troubleshooting on step 6.
- If the misfire counts are increasing every few engine revolutions (partially inactive cylinder), go to Single Cylinder Non-Continuous Misfire at Idle troubleshooting on step 21.
NO
The misfire affects multiple cylinders.
- If the misfire counts are increasing every engine revolution (completely inactive cylinder), go to Multiple Cylinder Continuous Misfire at Idle troubleshooting on step 30.
- If the misfire counts are increasing every few engine revolutions (partially inactive cylinder), go to Multiple Cylinder Non-Continuous Misfire at Idle troubleshooting on step 48.
-
- Problem verification - Static Load
-1. Increase the engine speed to 3, 500 rpm.
-2. Hold the engine speed steady, and monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Are the misfire counts increasing on any cylinder?
YES
The engine is misfiring under load. Go to step 4.
NO
The engine does not misfire under a static load. Go to step 5.
- Determine Affected Cylinders
-1. Continue to monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE Signal Current conditions Values Unit CYL4 MISFIRE Are misfire counts generally isolated to a single cylinder?
YES
The misfire is isolated to a single cylinder, go to Single Cylinder Misfire. Under Load troubleshooting on step 56.
NO
The misfire affects multiple cylinders, go to Multiple Cylinder Misfire. Under Load troubleshooting on step 63.
- Problem verification - On-board Snapshot
-1. Open the ONBOARD SNAPSHOT with the HDS.
-2. Scroll through the snapshot, and find when the MISFIRE value begins to increase.
-3. Record the value of these parameters as the MISFIRE value increases:
Signal Values Unit ECT SENSOR 1 deg. F ENGINE SPEED RPM VEHICLE SPEED MPH MAP SENSOR V TP SENSOR V -4. Drive the vehicle according to the conditions you identified above while monitoring the misfire counts.
Signal Current conditions Values Unit ECT SENSOR 1 ENGINE SPEED VEHICLE SPEED MAP SENSOR TP SENSOR Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Are the misfire counts increasing on any cylinder?
YES
The engine is misfiring under the specific operating conditions above.
- If the misfire occurred when the engine was cold, go to Misfire When Cold troubleshooting on step 70.
- If the misfire occurred when the engine was loaded, go to step 4.
NO
Intermittent failure; the engine is not misfiring at this time.NOTE: If the misfire can not be reproduced, there is a possibility that the problem may have been caused by poor quality fuel. The problem may have disappeared after refueling with fresh fuel. The MIL DIST (MIL Distance) value in the Data List in combination with the fuel level may help you make this determination.
- Check Ignition Coil Spark
-1. Turn the vehicle to the OFF (LOCK) mode.
-2. Remove the ignition coil from the problem cylinder.
-3. Connect a commercially available spark tester between the ignition coil and engine ground.
-4. Start the engine with the ignition coil connected.
Does the ignition coil produce a spark?
YES
The ignition coil wiring is OK. Go to step 14.
NO
There is a problem with the ignition coil, or the ignition coil circuit. Go to step 7.
- Ignition Coil Check
-1. Exchange the ignition coil on the problem cylinder with a normally operating cylinder.
-2. Connect a commercially available spark tester between the ignition coil and engine ground.
-3. Start the engine with the ignition coil connected.
Does the ignition coil produce a spark?
YES
The ignition coil has a failure. Replace the ignition coil .
NO
There is a problem with the ignition coil circuit. Go to step 8.
- Check Ignition Coil Power and Ground
-1. Disconnect the ignition coil 3P connector from the problem cylinder .
-2. Turn the vehicle to the ON mode.
-3. Measure the voltage between ignition coil 3P connector terminals No. 1 (power) and No. 2 (ground).
NOTE: After the vehicle is turned to the OFF (LOCK) mode, this circuit may still show battery voltage for a period of time. This is normal.
Is there battery voltage?
YES
The ignition coil power and ground circuits are OK. Go to step 9.
NO
There is a problem with the ignition coil power or ground circuit. Go to step 13.
- Check Ignition Coil Control Short to Power
-1. Turn the vehicle to the ON mode.
-2. Measure the voltage between ignition coil 3P connector terminals No. 3 (Ignition Control) and body ground.
Is there about 4 V or more?
YES
The ignition coil control circuit is shorted to power. Go to step 10.
NO
The ignition coil control circuit is not shorted to power. Go to step 11.
- Isolate Ignition Coil Control Short to Power
-1. Jump the SCS line with the HDS.
-2. Turn the vehicle to the OFF (LOCK) mode.
-3. Disconnect the PCM connectors.
-4. Turn the vehicle to the ON mode.
-5. Measure the voltage between ignition coil 3P connector terminals No. 3 (Ignition Control) and body ground.
Is there about 4 V or more?
YES
There is a short to power on the ignition coil control circuit. Find and repair the failure.
NO
The PCM is malfunctioning. Replace the PCM .
- Check Ignition Coil Control Open Circuit
-1. Turn the vehicle to the OFF (LOCK) mode.
-2. Jump the SCS line with the HDS.
-3. Disconnect the PCM connectors.
-4. Check for continuity between the ignition coil control terminal at the PCM connector and at ignition coil 3P connector terminal No. 3.
Is there continuity?
YES
The ignition coil control circuit is not open. Go to step 12.
NO
Repair the open circuit between the ignition coil and the PCM.
- Check Ignition Coil Control Short to Ground
-1. Check for continuity between the ignition coil control terminal at ignition coil 3P connector terminal No. 3 and body ground.
Is there continuity?
YES
Repair the short to ground on the ignition coil control wire.
NO
The ignition coil control wiring is OK. Substitute a known good PCM .
- Check Ignition Coil Power Circuit
-1. Measure the voltage between ignition coil 3P connector terminal No. 1 (power) and a known-good engine ground.
Is there battery voltage between the ignition coil power terminal and engine ground?
YES
The power circuit is OK. Repair the open circuit between the ignition coil (3P connector terminal No. 2) and G101.
NO
Repair the open circuit between the ignition coil and the ignition coil relay.
- Inspect Ignition Coil
-1. Inspect the ignition coil and spark plug tube for engine oil contamination.
Is the ignition coil covered in engine oil?
YES
Clean the oil from the ignition coil and spark plug tube. Replace the spark plug tube seals in the cylinder head cover .
NO
Go to step 15.
- Exchange Spark Plug and Ignition Coil
-1. Exchange the spark plug and the ignition coil with one from a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
The ignition coil and spark plug are OK. Go to step 17.
NO
There is a failure in the ignition coil or the spark plug. Go to step 16.
- Exchange Ignition Coil
-1. Exchange the ignition coil on the problem cylinder with a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
The spark plug has a failure. Replace the spark plug .
NO
The ignition coil has a failure. Replace the ignition coil .
- Check Cylinder Compression
-1. Perform a cylinder compression test .
-2. Record your test results in a chart similar to the one shown below.
Compression (PSI) No. 1 No. 2 No. 3 No. 4 Highest Reading (PSI) Lowest Reading (PSI) Variation (%) Does the compression vary more than 10 % between cylinders, or does any cylinder read below 150 PSI?
-
YES
The cylinder leakage is normal, but the engine compression is low. Check for each of the conditions below and repair as needed.
- Incorrect camshaft timing.
- A bent (short) connecting rod.
- Worn or damaged camshaft lobes.
NO
The engine compression and the cylinder leakage are normal. Go to step 18.
-
- Check Cylinder Leakage
-1. Perform a cylinder leakage test .
-2. Record your test results in the chart shown below.
Leakage (%) Leakage Area No. 1 No. 2 No. 3 No. 4 Does any cylinder have leakage greater than 10 %?
YES
If the majority of the air is escaping from exhaust pipe or throttle body, check for tight valve clearance and adjust valve clearance to specification (cold), then retest. Determine the cause of the cylinder leakage and repair the engine as needed.
NO
The cylinders are sealing properly. Go to step 19.
- Exchange Fuel Injector
-1. Exchange the fuel injector from the problem cylinder with one from another cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE Signal Current conditions Values Unit CYL4 MISFIRE Do the misfire counts stay on the problem cylinder when the fuel injector is swapped?
YES
The fuel injector is OK. Go to step 20.
NO
The fuel injector is faulty. Replace all injectors as a set .
- CKP Pattern Clear/Pattern Learn
-1. Select CRANK PATTERN in the ADJUSTMENT MENU with the HDS.
-2. Select CRANK PATTERN CLEAR, and clear the CKP pattern .
CRANK PATTERN CLEAR
Select CRANK PATTERN LEARNING with the HDS, and follow the screen prompts .
CRANK PATTERN LEARNING
Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
Update the PCM with the latest software or substitute a known-good PCM .
NO
The misfire problem has been fixed.
- Inspect Spark Plug
-1. Remove the spark plug from the problem cylinder.
-2. Inspect the spark plug for signs of failure. Also make sure the spark plugs are the correct part number for the vehicle.
Does the spark plug show any signs of failure or is it not the correct part number?
YES
NO
Go to step 22.
- Inspect Ignition Coil
-1. Inspect the ignition coil and the spark plug tube for engine oil contamination.
Is the ignition coil covered in engine oil?
YES
Clean the oil from the ignition coil and the spark plug tube. Replace the spark plug tube seals in the cylinder head cover .
NO
Go to step 23.
- Exchange Spark Plug and Ignition Coil
-1. Exchange the spark plug and the ignition coil with ones from a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
The ignition coil and spark plug are OK. Go to step 25.
NO
There is a failure in the ignition coil or the spark plug. Go to step 24.
- Exchange Ignition Coil
-1. Exchange the ignition coil on the problem cylinder with a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
The spark plug has a failure. Replace the spark plug .
NO
The ignition coil has a failure. Replace the ignition coil .
- Check MAP Sensor Fluctuation
-1. Start the engine, and let it idle until the cooling fans cycle twice.
-2. Turn off all engine and electrical loads (A/C, audio, lights, etc.).
-3. Configure a HIGH-SPEED SNAPSHOT, and select only the MAP SENSOR.
-4. Begin displaying live vehicle data on a line graph.
-5. Configure the MAP SENSOR line graph range for 1.2 V MAX and 0.8 V MIN.
-6. Watch the MAP SENSOR fluctuation. See examples below.
Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine hot?
YES
The intake manifold pressure fluctuation indicates a mechanical engine failure. Go to step 26.
NO
The intake manifold vacuum fluctuation is OK. Go to step 29.
- Adjust Valve Clearance
-1. Adjust the valve clearances , and inspect the camshaft for excessive wear or grooves.
NOTE: ECT Sensor 1 must read less than 100 deg. F (38 deg. C) before adjusting the valve clearance. Shortcutting this step may cause incorrect valve clearance and engine misfire.
-2. Recheck the MAP Sensor fluctuation at idle.
Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine hot?
YES
Adjusting the valve clearance did not correct the excessive MAP sensor fluctuation. Go to step 27.
NO
The excessive MAP sensor fluctuation was caused by incorrect valve clearance.
- Check Cylinder Compression
-1. Perform a cylinder compression test .
-2. Record your test results in a chart similar to the one shown below.
Compression (PSI) No. 1 No. 2 No. 3 No. 4 Highest Reading (PSI) Lowest Reading (PSI) Variation (%) Does the compression vary more than 10 % between cylinders, or does any cylinder read below 150 PSI?
-
YES
The cylinder leakage is normal, but the engine compression is low. Check for each of the conditions below and repair as needed.
- Incorrect camshaft timing.
- A bent (short) connecting rod.
- Worn or damaged camshaft lobes.
NO
The engine compression and the cylinder leakage are normal. Go to step 28.
-
- Check Cylinder Leakage
-1. Perform a cylinder leakage test .
-2. Record your test results in the chart shown below.
Leakage (%) Leakage Area No. 1 No. 2 No. 3 No. 4 Does any cylinder have leakage greater than 10 %?
YES
If the majority of the air is escaping from exhaust pipe or throttle body, check for tight valve clearance and adjust each cylinder as needed, then retest. Determine the cause of the cylinder leakage and repair the engine as needed.
NO
The cylinders are sealing properly. Go to step 29.
- Exchange Fuel Injector
-1. Exchange the fuel injector from the problem cylinder with one from another cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Do the misfire counts stay on the problem cylinder when the fuel injector is swapped?
YES
The fuel injector is OK. All of the failures have been checked for this type of misfire. Go to step 1 in the Problem verification procedure and ensure you selected the correct troubleshooting procedure.
NO
The fuel injector is faulty. Replace all injectors as a set .
- Inspect Spark Plug
-1. Remove the spark plug from the problem cylinder.
-2. Inspect the spark plug for signs of failure. Also make sure the spark plugs are the correct part number for the vehicle.
Does the spark plug show any signs of failure or is it not the correct part number?
YES
NO
Go to step 31.
- Check Ignition Coil Spark
-1. Turn the vehicle to the OFF (LOCK) mode.
-2. Remove the ignition coil from the problem cylinder.
-3. Connect a commercially available spark tester between the ignition coil and engine ground.
-4. Start the engine with the ignition coil connected.
Does the ignition coil produce a spark?
YES
The ignition coil wiring is OK. Go to step 39.
NO
There is a problem with the ignition coil, or the Ignition coil circuit. Go to step 32.
- Exchange Ignition Coil
-1. Exchange the ignition coil on the problem cylinder with a normally operating cylinder.
-2. Connect a commercially available spark tester between the ignition coil and engine ground.
-3. Start the engine with the ignition coil connected.
Does the ignition coil produce a spark?
YES
The ignition coil has a failure. Replace the ignition coil .
NO
There is a problem with the ignition coil circuit. Go to step 33.
- Check Ignition Coil Power and Ground
-1. Disconnect the ignition coil 3P connector from the problem cylinder .
-2. Turn the vehicle to the ON mode.
-3. Measure the voltage between ignition coil 3P connector terminals No. 1 (power) and No. 2 (ground).
NOTE: After the vehicle is turned to the OFF (LOCK) mode, this circuit may still show 12 volt battery voltage for a period of time. This is normal.
Is there battery voltage?
YES
The ignition coil power and ground circuits are OK. Go to step 34.
NO
There is a problem with the ignition coil power or ground circuit. Go to step 38.
- Check Ignition Coil Control Short to Power
-1. Turn the vehicle to the ON mode.
-2. Measure the voltage between ignition coil 3P connector terminals No. 3 (Ignition Control) and body ground.
Is there about 4 V or more?
YES
The ignition coil control circuit is shorted to power. Go to step 35.
NO
The ignition coil control circuit is not shorted to power. Go to step 36.
- Isolate Ignition Coil Control Short to Power
-1. Jump the SCS line with the HDS.
-2. Turn the vehicle to the OFF (LOCK) mode.
-3. Disconnect the PCM connectors.
-4. Turn the vehicle to the ON mode.
-5. Measure the voltage between ignition coil 3P connector terminals No. 3 (Ignition Control) and body ground.
Is there about 4 V or more?
YES
There is a short to power on the ignition coil control circuit. Find and repair the failure.
NO
The PCM is malfunctioning. Replace the PCM .
- Check Ignition Coil Control Open Circuit
-1. Turn the vehicle to the OFF (LOCK) mode.
-2. Jump the SCS line with the HDS.
-3. Disconnect the PCM connectors.
-4. Check for continuity between the ignition coil control terminal at the PCM connector and at the ignition coil 3P connector terminal No. 3.
Is there continuity?
YES
The ignition coil control circuit is not open. Go to step 37.
NO
Repair the open circuit between the ignition coil and the PCM.
- Check Ignition Coil Control Short to Ground
-1. Check for continuity between ignition coil control terminal at the ignition coil 3P connector terminal No. 3 (Ignition Control) and body ground.
Is there continuity?
YES
Repair the short to ground on the ignition coil control wire.
NO
The ignition coil control wiring is OK. Substitute a known good PCM .
- Check Ignition Coil Power Circuit
-1. Measure the voltage between ignition coil 3P connector terminal No. 1 (power) and a known-good engine ground.
Is there battery voltage between the ignition coil power terminal and engine ground?
YES
The power circuit is OK. Repair the open circuit between the ignition coil (3P connector terminal No. 2) and G101.
NO
Repair the open circuit between the ignition coil and the ignition coil relay.
- Inspect Ignition Coil
-1. Inspect the ignition coil and spark plug tube for engine oil contamination.
Is the ignition coil covered in engine oil?
YES
Clean the oil from the ignition coil and spark plug tube. Replace the spark plug tube seals in the cylinder head cover .
NO
Go to step 40.
- Exchange Spark Plug and Ignition Coil
-1. Exchange the spark plug and the ignition coil with one from a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
The ignition coil and spark plug are OK. Go to step 42.
NO
There is a failure in the ignition coil or the spark plug. Go to step 41.
- Exchange Ignition Coil
-1. Exchange the ignition coil on the problem cylinder with a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
The spark plug has a failure. Replace the spark plug .
NO
The ignition coil has a failure. Replace the ignition coil .
- Check MAP Sensor Fluctuation
-1. Start the engine, and let it idle until the cooling fans cycle twice.
-2. Turn off all engine and electrical loads (A/C, audio, lights, etc.).
-3. Configure a HIGH-SPEED SNAPSHOT, and select only the MAP SENSOR.
-4. Begin displaying live vehicle data on a line graph.
-5. Configure the MAP SENSOR line graph range for 1.2 V MAX and 0.8 V MIN.
-6. Watch the MAP SENSOR fluctuation. See examples below.
Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine hot?
YES
The intake manifold pressure fluctuation indicates a mechanical engine failure. Go to step 43.
NO
The intake manifold vacuum fluctuation is OK. Go to step 46.
- Adjust Valve Clearance
-1. Adjust the valve clearances , and inspect the camshaft for excessive wear or grooves.
NOTE: ECT Sensor 1 must read less than 100 deg. F (38 deg. C) before adjusting the valve clearance. Shortcutting this step may cause incorrect valve clearance and engine misfire.
-2. Recheck the MAP Sensor fluctuation at idle.
Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine hot?
YES
Adjusting the valve clearance did not correct the excessive MAP sensor fluctuation. Go to step 44.
NO
The excessive MAP sensor fluctuation was caused by incorrect valve clearance.
- Check Cylinder Compression
-1. Perform a cylinder compression test .
-2. Record your test results in a chart similar to the one shown below.
Compression (PSI) No. 1 No. 2 No. 3 No. 4 Highest Reading (PSI) Lowest Reading (PSI) Variation (%) Does the compression vary more than 10 % between cylinders, or does any cylinder read below 150 PSI?
-
YES
The cylinder leakage is normal, but the engine compression is low. Check for each of the conditions below and repair as needed.
- Incorrect camshaft timing.
- A bent (short) connecting rod.
- Worn or damaged camshaft lobes.
NO
The engine compression and the cylinder leakage are normal. Go to step 45.
-
- Check Cylinder Leakage
-1. Perform a cylinder leakage test .
-2. Record your test results in the chart shown below.
Leakage (%) Leakage Area No. 1 No. 2 No. 3 No. 4 Does any cylinder have leakage greater than 10 %?
YES
If the majority of the air is escaping from exhaust pipe or throttle body, check for tight valve clearance and adjust each cylinder as needed, then retest. Determine the cause of the cylinder leakage and repair the engine as needed.
NO
The cylinders are sealing properly. Go to step 46.
- Exchange Fuel Injector
-1. Exchange the fuel injector from the problem cylinder with one from another cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Do the misfire counts stay on the problem cylinder when the fuel injector is swapped?
YES
The fuel injector is OK. Go to step 47.
NO
The fuel injector is faulty. Replace all injectors as a set .
- CKP Pattern Clear/Pattern Learn
-1. Select CRANK PATTERN in the ADJUSTMENT MENU with the HDS.
-2. Select CRANK PATTERN CLEAR, and clear the CKP pattern .
CRANK PATTERN CLEAR
Select CRANK PATTERN LEARNING with the HDS, and follow the screen prompts .
CRANK PATTERN LEARNING
Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
Update the PCM with the latest software or substitute a known-good PCM .
NO
The misfire problem has been fixed.
- Inspect Spark Plug
-1. Remove the spark plug from the problem cylinder.
-2. Inspect the spark plug for signs of failure. Also make sure the spark plugs are the correct part number for the vehicle.
Does the spark plug show any signs of failure or is it not the correct part number?
YES
NO
Go to step 49.
- Check MAP Sensor Fluctuation
-1. Start the engine, and let it idle until the cooling fans cycle twice.
-2. Turn off all engine and electrical loads (A/C, audio, lights, etc.).
-3. Configure a HIGH-SPEED SNAPSHOT, and select only the MAP SENSOR.
-4. Begin displaying live vehicle data on a line graph.
-5. Configure the MAP SENSOR line graph range for 1.2 V MAX and 0.8 V MIN.
-6. Watch the MAP SENSOR fluctuation. See examples below.
Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine hot?
YES
The intake manifold pressure fluctuation indicates a mechanical engine failure. Go to step 50.
NO
The intake manifold vacuum fluctuation is OK. Go to step 53.
- Adjust Valve Clearance
-1. Adjust the valve clearances , and inspect the camshaft for excessive wear or grooves.
NOTE: ECT Sensor 1 must read less than 100 deg. F (38 deg. C) before adjusting the valve clearance. Shortcutting this step may cause incorrect valve clearance and engine misfire.
-2. Recheck the MAP Sensor fluctuation at idle.
Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine hot?
YES
Adjusting the valve clearance did not correct the excessive MAP sensor fluctuation. Go to step 51.
NO
The excessive MAP sensor fluctuation was caused by incorrect valve clearance.
- Check Cylinder Compression
-1. Perform a cylinder compression test .
-2. Record your test results in a chart similar to the one shown below.
Compression (PSI) No. 1 No. 2 No. 3 No. 4 Highest Reading (PSI) Lowest Reading (PSI) Variation (%) Does the compression vary more than 10 % between cylinders, or does any cylinder read below 150 PSI?
-
YES
The cylinder leakage is normal, but the engine compression is low. Check for each of the conditions below and repair as needed.
- Incorrect camshaft timing.
- A bent (short) connecting rod.
- Worn or damaged camshaft lobes.
NO
The engine compression and the cylinder leakage are normal. Go to step 52.
-
- Check Cylinder Leakage
-1. Perform a cylinder leakage test .
-2. Record your test results in the chart shown below.
Leakage (%) Leakage Area No. 1 No. 2 No. 3 No. 4 Does any cylinder have leakage greater than 10 %?
YES
If the majority of the air is escaping from exhaust pipe or throttle body, check for tight valve clearance and adjust each cylinder as needed, then retest. Determine the cause of the cylinder leakage and repair the engine as needed.
NO
The cylinders are sealing properly. Go to step 53.
- Check Fuel Pressure
-1. Relieve the fuel pressure .
-2. Attach the fuel pressure gauge set and the fuel pressure gauge .
-3. Locate and record the fuel pressure specification for your vehicle.
Minimum Pressure (kPa) Maximum Pressure (kPa) -4. Start the engine, and record the fuel pressure under the conditions the misfire was duplicated.
Fuel Pressure (kPa) Is the fuel pressure within specifications?
YES
The fuel pressure is OK. Go to step 54.
NO
Check for pinched or damaged fuel lines. If OK, replace the fuel tank unit .
- Check Fuel Contamination
-1. Remove the fuel tank unit .
-2. Inspect for evidence of fuel contamination such as diesel fuel, water, rust, or debris.
NOTE: If the misfire occurred shortly after refueling, the likely cause is poor fuel quality. The MIL DIST (MIL distance) value in the DATA LIST, along with the fuel level, can help you make this determination. Incorrect or contaminated fuel typically affects multiple cylinders. But a problem such as water in the fuel can cause a single cylinder misfire that occurs randomly.
Is there evidence of fuel contamination?
YES
Replace the fuel filter and then drain/refill the fuel tank with known-good fuel.
NO
The fuel system has no signs of fuel contamination. Go to step 55.
- Check MAF Sensor g/s
-1. Locate and record the MAF SENSOR g/s specification for your vehicle. This can be found in troubleshooting procedure for DTC P0171 .
Minimum g/s Maximum g/s Specified RPM -2. Ensure the vehicle meets these conditions:
- Engine coolant temperature (ECT SENSOR 1) above 176 deg. F (80 deg. C)
- CVT in P or N, M/T in neutral
- All electrical loads off
Signal Current conditions Values Unit ECT SENSOR 1 -3. Monitor the ENGINE SPEED in the DATA LIST with the HDS. Raise and hold the engine speed steady at the specified rpm.
Signal Current conditions Values Unit ENGINE SPEED -4. While holding the rpm steady, check the MAF SENSOR in the DATA LIST.
Signal Current conditions Values Unit MAF SENSOR Is the MAF Sensor g/s value within specifications?
YES
The MAF sensor is reading correctly. Replace all fuel injectors as a set .
NO
The MAF sensor is not reading correctly. Replace MAF sensor/IAT sensor .
- Inspect Spark Plug
-1. Remove the spark plug from the problem cylinder.
-2. Inspect the spark plug for signs of failure. Also make sure the spark plugs are the correct part number for the vehicle.
Does the spark plug show any signs of failure or is it not the correct part number?
YES
NO
Go to step 57.
- Inspect Ignition Coil
-1. Inspect the ignition coil and the spark plug tube for engine oil contamination.
Is the ignition coil covered in engine oil?
YES
Clean the oil from the ignition coil and the spark plug tube. Replace the spark plug tube seals in the cylinder head cover .
NO
Go to step 58.
- Exchange Spark Plug and Ignition Coil
-1. Exchange the spark plug and the ignition coil with ones from a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
The ignition coil and the spark plug are OK. Go to step 60.
NO
There is a failure in the ignition coil or the spark plug. Go to step 59.
- Exchange Ignition Coil
-1. Exchange the ignition coil on the problem cylinder with a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
The spark plug has a failure. Replace the spark plug .
NO
The ignition coil has a failure. Replace the ignition coil .
- Exchange Fuel Injector
-1. Exchange the fuel injector from the problem cylinder with one from another cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE Signal Current conditions Values Unit CYL3 MISFIRE CYL4 MISFIRE Do the misfire counts stay on the problem cylinder when the fuel injector is swapped?
YES
The fuel injector is OK. Go to step 61.
NO
The fuel injector is faulty. Replace all injectors as a set .
- Inspect VTEC System
-1. Perform the VTEC rocker arm test .
Does the engine pass the VTEC rocker arm test?
YES
Go to step 62.
NO
Repair the VTEC system.
- CKP Pattern Clear/Pattern Learn
-1. Select CRANK PATTERN in the ADJUSTMENT MENU with the HDS.
-2. Select CRANK PATTERN CLEAR, and clear the CKP pattern .
CRANK PATTERN CLEAR
Select CRANK PATTERN LEARNING with the HDS, and follow the screen prompts .
CRANK PATTERN LEARNING
Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
Update the PCM with the latest software or substitute a known-good PCM .
NO
The misfire problem has been fixed.
- Inspect Spark Plug
-1. Remove the spark plug from the problem cylinder.
-2. Inspect the spark plug for signs of failure. Also make sure the spark plugs are the correct part number for the vehicle.
Does the spark plug show any signs of failure or is it not the correct part number?
YES
NO
Go to step 64.
- Check Fuel Pressure
-1. Relieve the fuel pressure .
-2. Attach the fuel pressure gauge set and the fuel pressure gauge .
-3. Locate and record the fuel pressure specification for your vehicle.
Minimum Pressure (kPa) Maximum Pressure (kPa) -4. Start the engine, and record the fuel pressure under the conditions the misfire was duplicated.
Fuel Pressure (kPa) Is the fuel pressure within specifications?
YES
The fuel pressure is OK. Go to step 65.
NO
Check for pinched or damaged fuel lines. If OK, replace the fuel tank unit .
- Check Fuel Contamination
-1. Remove the fuel tank unit .
-2. Inspect for evidence of fuel contamination such as diesel fuel, water, rust, or debris.
NOTE: If the misfire occurred shortly after refueling, the likely cause is poor fuel quality. The MIL DIST (MIL distance) value in the DATA LIST, along with the fuel level, can help you make this determination. Incorrect or contaminated fuel typically affects multiple cylinders. But a problem such as water in the fuel can cause a single cylinder misfire that occurs randomly.
Is there evidence of fuel contamination?
YES
Replace the fuel filter and then drain/refill the fuel tank with a known-good fuel.
NO
The fuel system has no signs of fuel contamination. Go to step 66.
- Exchange Fuel Injector
-1. Exchange the fuel injector from the problem cylinder with one from another cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Do the misfire counts stay on the problem cylinder when the fuel injector is swapped?
YES
The fuel injector is OK. Go to step 67.
NO
The fuel injector is faulty. Replace all injectors as a set .
- Inspect VTEC System
-1. Perform the VTEC rocker arm test .
Does the engine pass the VTEC rocker arm test?
YES
Go to step 68.
NO
Repair the VTEC system.
- Check for Exhaust Restrictions
-1. Reinstall all removed parts, and reconnect all connectors.
-2. Record the MAP SENSOR value while the engine is off.
Signal Current conditions Values Unit MAP SENSOR -3. Start the engine, and monitor the ENGINE SPEED and MAP SENSOR in the DATA LIST with the HDS.
Signal Current conditions Values Unit MAP SENSOR ENGINE SPEED -4. Raise the engine speed to 3, 500 rpm and hold the throttle steady.
Does the MAP SENSOR read near atmospheric pressure (engine off value)?
YES
There is a restriction in the exhaust system. Check for catalyst damage and repair as necessary.
NO
Go to step 69.
- CKP Pattern Clear/Pattern Learn
-1. Select CRANK PATTERN in the ADJUSTMENT MENU with the HDS.
-2. Select CRANK PATTERN CLEAR, and clear the CKP pattern .
CRANK PATTERN CLEAR
Select CRANK PATTERN LEARNING with the HDS, and follow the screen prompts .
CRANK PATTERN LEARNING
Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE Signal Current conditions Values Unit CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
Update the PCM with the latest software or substitute a known-good PCM .
NO
The misfire problem has been fixed.
- Check MAP Sensor Fluctuation
-1. Start the engine, and let it idle until the cooling fans cycle twice.
-2. Turn off all engine and electrical loads (A/C, audio, lights, etc.).
-3. Configure a HIGH-SPEED SNAPSHOT, and select only the MAP SENSOR.
-4. Begin displaying live vehicle data on a line graph.
-5. Configure the MAP SENSOR line graph range for 1.2 V MAX and 0.8 V MIN.
-6. Watch the MAP SENSOR fluctuation. See examples below.
Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine hot?
YES
The intake manifold pressure fluctuation indicates a mechanical engine failure. Go to step 71.
NO
The intake manifold vacuum fluctuation is OK. Go to step 74.
- Adjust Valve Clearance
-1. Adjust the valve clearances, and inspect the camshaft for excessive wear or grooves.
NOTE: ECT Sensor 1 must read less than 100 deg. F (38 deg. C) before adjusting the valve clearance. Shortcutting this step may cause incorrect valve clearance and engine misfire.
-2. Recheck the MAP Sensor fluctuation at idle.
Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine hot?
YES
Adjusting the valve clearance did not correct the excessive MAP sensor fluctuation. Go to step 72.
NO
The excessive MAP sensor fluctuation was caused by incorrect valve clearance.
- Check Cylinder Compression
-1. Perform a cylinder compression test .
-2. Record your test results in a chart similar to the one shown below.
Compression (PSI) No. 1 No. 2 No. 3 No. 4 Highest Reading (PSI) Lowest Reading (PSI) Variation (%) Does the compression vary more than 10 % between cylinders, or does any cylinder read below 150 PSI?
-
YES
The cylinder leakage is normal, but the engine compression is low. Check for each of the conditions below and repair as needed.
- Incorrect camshaft timing.
- A bent (short) connecting rod.
- Worn or damaged camshaft lobes.
NO
The engine compression and the cylinder leakage are normal. Go to step 73.
-
- Check Cylinder Leakage
-1. Perform a cylinder leakage test .
-2. Record your test results in the chart shown below.
Leakage (%) Leakage Area No. 1 No. 2 No. 3 No. 4 Does any cylinder have leakage greater than 10 %?
YES
If the majority of the air is escaping from exhaust pipe or throttle body, check for tight valve clearance and adjust each cylinder as needed, then retest. Determine the cause of the cylinder leakage and repair the engine as needed.
NO
The cylinders are sealing properly. Go to step 74.
- Check Fuel Injector Leak Down
-1. Connect the fuel pressure gauge set .
-2. Ensure that the fuel shut off valve is on the fuel pump side of the pressure gauge.
-3. Start the engine, and then shut it off.
-4. Turn the shut off valve 90 deg. to isolate the pressure between the fuel injectors and the fuel pressure gauge.
-5. Record the initial fuel pressure reading.
-6. Let the vehicle sit for 10 minutes.
-7. Check the fuel pressure.
Does the pressure drop more than 10 PSI within 10 minutes?
YES
The fuel injectors are leaking. Replace all fuel injectors as a set .
NO
Go to step 75.
- Inspect Spark Plug
-1. Remove the spark plug from the problem cylinder .
-2. Inspect the spark plug for signs of failure. Also make sure the spark plugs are the correct part number for the vehicle.
Does the spark plug show any signs of failure or is it not the correct part number?
YES
NO
Go to step 76.
- Exchange Spark Plug and Ignition Coil
-1. Exchange the spark plug and the ignition coil with ones from a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
The ignition coil and the spark plug are OK. Go to step 78.
NO
There is a failure in the ignition coil or the spark plug. Go to step 77.
- Exchange Ignition Coil
-1. Exchange the ignition coil on the problem cylinder with a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay on the problem cylinder?
YES
The spark plug has a failure. Replace the spark plug
NO
The ignition coil has a failure. Replace the ignition coil .
- Engine Carbon Removal
-1. Perform a top engine cleaning following the product manufacturer's instructions.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor the misfire parameters in the DATA LIST.
Signal Current conditions Values Unit CYL1 MISFIRE CYL2 MISFIRE CYL3 MISFIRE CYL4 MISFIRE Did the misfire counts stay?
YES
The carbon removal procedure did not correct the misfire. Replace all fuel injectors as a set .
NO
The carbon removal procedure corrected the misfire.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.