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 P0172
DTC P0172 : Fuel System Too Rich
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 P0172, troubleshoot those DTCs first, then recheck for P0172.
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 |
|---|---|---|---|
| P0172 Fuel System Too Rich |
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) Less than 0.79 Do the current condition (s) match the threshold?
YES
The AF FB (ST FUEL TRIM) is too low 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 lowest 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) Less than 0.79 Do the current condition (s) match the threshold under the on-board snapshot conditions?
YES
AF FB (ST FUEL TRIM) is too low 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 Engine Oil
-1. Start the engine, and let it idle.
-2. Gently 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) Less than 0.79 Do the current condition (s) match the threshold?
YES
The engine oil is contaminated. Replace the engine oil and engine oil filter .
NO
The engine oil is OK. Go to step 4.
- 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 6.
NO
The MAF sensor is reading incorrectly. Inspect for a cracked, damaged, or incorrectly installed air cleaner assembly. If OK, Go to step 5.
- 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. If OK, replace MAF sensor/IAT sensor .
NO
Reinstall the MAF sensor/IAT sensor , then go to step 6.
- Check Fuel Pressure
-1. Check the fuel pressure under the conditions when AF FB (ST FUEL TRIM) is 0.79 or less.
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 7.
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 0.79 or less.
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) Less than 0.79 Do the current condition (s) match the threshold under the on-board snapshot conditions?
YES
The fuel is not the cause of the low AF FB (ST FUEL TRIM) value. Go to step 8.
NO
The fuel was causing the low 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 0.79 or less.
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) Less than 0.79 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 low AF FB (ST FUEL TRIM) value. Reinstall the original A/F sensor, then go to step 9.
NO
The A/F sensor (Sensor 1) was causing the low 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 0.79 or less.
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) Less than 0.79 Do the current condition (s) match the threshold under the on-board snapshot conditions?
YES
The injectors are not the cause of the low AF FB (ST FUEL TRIM) value. Substitute a known-good PCM .
NO
The injectors were causing the low 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.