DTC Troubleshooting

DTC Troubleshooting: P0171, P0172, P0171, P0172

DTC P0171:

Fuel System Too Lean

DTC P0172:

Fuel System Too Rich

NOTE:

- Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information Initial Inspection and Diagnostic Overview.
- Poor fuel quality can also cause DTC P0171.
- If any of the DTCs listed below are stored at the same time as DTC P0171 and/or P0172, troubleshoot those DTCs first, then recheck for P0171 and/or P0172.
P0101, P0102, P0103: MAF sensor
P0107, P0108, P1128, P1129: MAP sensor
P0133, P1172, P1157, P2195, P2238, P2252, P2A00: A/F sensor (Sensor 1)
P0134, P0135: A/F sensor (Sensor 1) heater
P0137, P0138, P0139: Secondary HO2S (Sensor 2)
P0141: Secondary HO2S (Sensor 2) heater
P0443, P0496: EVAP canister purge valve
P2646, P2647, P2648, P2649: VTEC system

1. Check the fuel pressure Testing and Inspection.

Is the fuel pressure OK?

YES -

Go to step 2.

NO -

Check these items:

- If the pressure is too high, replace the fuel pressure regulator Service and Repair, then go to step 6.
- If the pressure is too low, check the fuel pump, the fuel feed pipe, and the fuel filter. If they are OK, replace the fuel pressure regulator Service and Repair, then go to step 6.

2. Check for vacuum leaks at these parts:

- PCV valve
- PCV hose
- EVAP canister purge valve
- Throttle body
- Intake manifold
- Brake booster
- Brake booster hose
- Intake air duct

Are the parts OK?

YES -

Go to step 3.

NO -

Repair or replace parts with leaks, then go to step 6.

3. Start the engine. Hold the engine speed at 3,000 rpm without load (A/T in P or N, M/T in neutral) until the radiator fan comes on, then let it idle.

4. Check under these conditions:

- Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)
- A/T in N, M/T in neutral
- All electrical loads off

5. Monitor the ENGINE SPEED in the DATA LIST with the HDS. Raise and hold the engine speed at 2,500 rpm. While holding the rpm steady, check the MAF SENSOR in the DATA LIST.

Is there about 7.0-8.6 gm/s?

YES -

Replace the injectors Service and Repair, then go to step 6.

NO -

Replace the MAF sensor/IAT sensor Service and Repair, then go to step 6.

6. Turn the ignition switch to ON (II).

7. Reset the ECM/PCM with the HDS.

8. Do the ECM/PCM idle learn procedure ECM/PCM Idle Learn Procedure (M/T).

9. Start the engine. Hold the engine speed at 3,000 rpm without load (A/T in P or N, M/T in neutral) until the radiator fan comes on, then let it idle.

10. Test-drive under these conditions:

- Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)
- A/T in D, M/T in 4th
- Drive at a steady speed between 15-75 mph (24-120 km/h) for 15 minutes

NOTE: DTC P0171 and/or P0172 may take up to 40 minutes of test driving to set. Using the HDS, monitor the short term fuel trim (ST FUEL TRIM). If the ST FUEL TRIM stays within 0.8-1.3, there is no problem at this time.

11. Check for Pending or Confirmed DTCs with the HDS.

Is DTC P0171 or P0172 indicated?

YES -

Go to step 1.

NO -

Troubleshooting is complete. If any other Pending or Confirmed DTCs are indicated, go to the indicated DTC's troubleshooting.�