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 P0171 (KA/Kc)
DTC P0171 : Fuel System Too Lean
NOTE:
- Before you troubleshoot, review the general troubleshooting information .
- Do not clear the DTC or reset the PCM before beginning this troubleshooting procedure until instructed to clear it. Clearing the DTC or resetting the PCM can delete valuable diagnostic information, even if the on-board snapshot and the freeze data is saved.
- Inspect for aftermarket fuel system and engine components before beginning troubleshooting.
- If any of the DTCs listed below are stored at the same time as DTC P0171, troubleshoot those DTCs first, then recheck for P0171.
P0101, P0102, P0103: MAF sensor
P0107, P0108, P2073, P2074: MAP sensor
P0133, P1157, P1172, P2195, P219A, P2238, P2252, P2A00: A/F sensor (Sensor 1)
P0134, P0135: A/F sensor (Sensor 1) heater
P0137, P0138, P0139, P2270: Secondary HO2S (Sensor 2)
P0141: Secondary HO2S (Sensor 2) heater
P0201, P0202, P0203, P0204: Fuel injector
P0455, P0456, P0496, P0497, P0498, P0499, P145C, P2422,: EVAP canister purge valve
P2646, P2647, P2648, P2649: VTEC system
P0400, P0401, P0404, P0406, P2413: EGR system
P0365, P0369: CMP sensor
| DTC Description | Confirmed DTC | Pending DTC | Freeze Frame |
|---|---|---|---|
| P0171 Fuel System Too Lean |
DTC (PGM-FI)
- Problem verification-Idle
-1. Start the engine, and let it idle without load (CVT in P or N, M/T in neutral).
-2. Check the parameter (s) below with the HDS.
Signal Threshold Current conditions Values Unit Values Unit AF FB (ST FUEL TRIM) More than 1.32 Do the current condition (s) match the threshold?
YES
The AF FB (ST FUEL TRIM) is too high at idle. Go to step 3.
NO
The AF FB (ST FUEL TRIM) is OK at idle. Go to step 2.
- Problem verification-On-board Snapshot
-1. Review the on-board snapshot and record the value of the parameters below when AF FB (ST FUEL TRIM) was at its highest point.
ENGINE SPEED VEHICLE SPEED REL TP SENSOR APP SENSOR On-board Snapshot
-2. Drive the vehicle according to the conditions determined above.
Signal Current conditions Values Unit ENGINE SPEED VEHICLE SPEED REL TP SENSOR APP SENSOR -3. Check the parameter (s) below with the HDS while driving.
Signal Threshold Current conditions Values Unit Values Unit AF FB (ST FUEL TRIM) More than 1.32 Do the current condition (s) match the threshold under the on-board snapshot conditions?
YES
AF FB (ST FUEL TRIM) is too high under the conditions above. Go to step 3.
NO
AF FB (ST FUEL TRIM) is OK under the same conditions as the on-board snapshot. The system is normal at this time.
- Check for MAF Sensor Debris
-1. Turn the vehicle to the OFF (LOCK) mode.
-2. Remove the MAF sensor/IAT sensor .
-3. Check for lint, bugs, and other foreign objects in the sensor.
Is there debris in the MAF sensor?
YES
Remove the debris from the MAF sensor and then use a vacuum cleaner to remove any debris from the air cleaner housing.
NO
Reinstall the MAF sensor/IAT sensor , then go to step 4.
- Check for Disconnected or Damaged Components:
Visually inspect each of the components below for disconnected hoses, cracks, or damage:
- Crankcase breather hose (A)
- Air cleaner housing (B)
- Oil cap (C) and dipstick (D)
Are any components disconnected or damaged?
YES
Repair as necessary.
NO
Go to step 5.
- Check Brake Booster
-1. Continue to let the engine idle.
-2. Pinch the brake booster vacuum hose (A) connecting to the intake manifold.
-3. Check the parameter (s) below with the HDS with the vacuum hose pinched.
Signal Threshold Current conditions Values Unit Values Unit AF FB (ST FUEL TRIM) More than 1.32 Do the current condition (s) match the threshold?
YES
The brake booster is not leaking. Go to step 6.
NO
There is a leak in the brake booster or hoses. Check the brake booster vacuum hoses for leaks. If no leaks are found, replace the brake booster .
- Check PCV System
-1. Continue to let the engine idle.
-2. Pinch the PCV vacuum hose (A).
-3. Check the parameter (s) below with the HDS with the vacuum hose pinched.
Signal Threshold Current conditions Values Unit Values Unit AF FB (ST FUEL TRIM) More than 1.32 Do the current condition (s) match the threshold?
YES
The PCV system is not leaking. Go to step 7.
NO
There is a leak in the PCV system. Check the vacuum hoses for leaks and repair as needed.
- Check for Intake Manifold Vacuum Leaks
-1. Disconnect the intake air duct from the air cleaner housing.
-2. Connect a large intake manifold adaptor cone into the intake air duct from the OTC LeakMaster evaporative emissions system tester kit.
-3. Use the OTC LeakMaster evaporative emissions system tester to direct smoke into the intake manifold.
-4. Inspect each of the areas below for signs of leaks:
- Intake manifold and gaskets
- Throttle body and gasket
- Air intake ducting
- All vacuum and air hoses
Are there any leaks?
YES
Repair the vacuum leak.
NO
The intake manifold is not leaking. Go to step 8.
- Check MAF Sensor Reading
-1. Start the engine and hold the engine speed at 3, 000 rpm until the radiator fan comes on.
-2. Make sure the following conditions are met:
- ECT Sensor 1 above 158 deg. F (70 deg. C)
- CVT in P or N, M/T in neutral
- All engine and electrical loads turned off
Signal Current conditions Values Unit ECT SENSOR 1 -3. Monitor the ENGINE SPEED in the DATA LIST with the HDS, then hold the engine speed at 2, 500 rpm with the accelerator pedal held steady.
Signal Current conditions Values Unit ENGINE SPEED -4. Check the parameter (s) below with the HDS at 2, 500 rpm for 30 seconds, check the parameter (s) below with the HDS.
Signal Threshold Current conditions Values Unit Values Unit MAF SENSOR 4.9-6.9 g/s Do the current condition (s) match the threshold?
YES
The MAF sensor is OK. Go to step 9.
NO
The MAF sensor is reading incorrectly. Inspect for a cracked, damaged, or incorrectly installed air cleaner assembly. If OK, Replace the MAF sensor/IAT sensor .
- Check Fuel Pressure
-1. Check the fuel pressure under the conditions when AF FB (ST FUEL TRIM) is 1.32 or more.
Signal Current conditions Values Unit AF FB (ST FUEL TRIM) Is the fuel pressure between 390-440 kPa (3.98-4.49 kgf/cm 2, 56.6-63.8 psi)?
YES
The fuel pressure is OK. Go to step 10.
NO
- Replace Fuel:NOTE:
There is an increased likelihood of a fuel related issue if the misfire appeared shortly after refueling. The MIL DIST (MIL Distance) value in the DATA LIST in combination with the fuel level may help you make this determination.
-1. Drain and refill the fuel tank with known-good fuel .
-2. Operate the vehicle under the same conditions where AF FB (ST FUEL TRIM) was 1.32 or more.
ENGINE SPEED VEHICLE SPEED REL TP SENSOR APP SENSOR On-board Snapshot
Signal Current conditions Values Unit ENGINE SPEED VEHICLE SPEED REL TP SENSOR APP SENSOR -3. Check the parameter (s) below with the HDS while driving.
Signal Threshold Current conditions Values Unit Values Unit AF FB (ST FUEL TRIM) More than 1.32 Do the current condition (s) match the threshold under the on-board snapshot conditions?
YES
The fuel is not the cause of the high AF FB (ST FUEL TRIM) value. Go to step 11.
NO
The fuel was causing the high AF FB (ST FUEL TRIM) value.
- Replace A/F Sensor (Sensor 1)
-1. Replace the A/F sensor (Sensor 1) with a known-good sensor.
-2. Operate the vehicle under the same conditions where AF FB (ST FUEL TRIM) was 1.32 or more.
ENGINE SPEED VEHICLE SPEED REL TP SENSOR APP SENSOR On-board Snapshot
Signal Current conditions Values Unit ENGINE SPEED VEHICLE SPEED REL TP SENSOR APP SENSOR -3. Check the parameter (s) below with the HDS while driving.
Signal Threshold Current conditions Values Unit Values Unit AF FB (ST FUEL TRIM) More than 1.32 Do the current condition (s) match the threshold under the on-board snapshot conditions?
YES
The A/F sensor (Sensor 1) is not the cause of the high AF FB (ST FUEL TRIM) value. Go to sep 12.
NO
The A/F sensor (Sensor 1) was causing the high AF FB (ST FUEL TRIM) value. Replace the original A/F sensor (Sensor 1) .
- Replace Injectors
-1. Replace the injectors with known-good injectors.
-2. Operate the vehicle under the same conditions where AF FB (ST FUEL TRIM) was 1.32 or more.
ENGINE SPEED VEHICLE SPEED REL TP SENSOR APP SENSOR On-board Snapshot
Signal Current conditions Values Unit ENGINE SPEED VEHICLE SPEED REL TP SENSOR APP SENSOR -3. Check the parameter (s) below with the HDS while driving.
Signal Threshold Current conditions Values Unit Values Unit AF FB (ST FUEL TRIM) More than 1.32 Do the current condition (s) match the threshold under the on-board snapshot conditions?
YES
The injectors are not the cause of the high AF FB (ST FUEL TRIM) value. Substitute a known-good PCM .
NO
The injectors were causing the high AF FB (ST FUEL TRIM) value. Replace the original injectors .
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.