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DTC Troubleshooting: P0171 (45), P0172 (45)

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.
  • If some of the DTCs listed below are indicated at the same time as DTC P0171 and/or P0172, troubleshoot those DTCs first, then recheck for P0171 and/or P0172.
    P0102, P0103: Mass air flow (MAF) sensor
    P0107, P0108: Manifold absolute pressure (MAP) sensor
    P0133, P1157, P2238, P2252, P2A00: Air fuel ratio (A/F) sensor (Sensor 1)
    P0134, P0135: Air fuel ratio (A/F) sensor (Sensor 1) heater
    P0137, P0138, P0139: Secondary HO2S (Sensor 2)
    P0141: Secondary HO2S (Sensor 2) heater
    P2648, P2649: VTEC system
    P0443: EVAP canister purge valve
Is the fuel pressure OK?
YES -
Go to Step 2 .
NO -
  1. Check for vacuum leaks at these parts:
    • PCV valve
    • PCV hose
    • EVAP canister purge valve
    • Throttle body
    • Intake manifold
    • Brake booster hose
    • Brake booster
    • Intake air duct
Are the parts OK?
YES -
Go to Step 3 .
NO -
Repair or replace parts with leaks, then go to Step 10 .
  1. Turn the ignition switch to LOCK (0).
  1. Disconnect the vacuum hose (A) from the EVAP canister purge valve (B), and connect a vacuum pump/gauge to the EVAP canister purge valve.
  1. Apply vacuum to the hose.
Does the hold vacuum?
YES -
Go to Step 6 .
NO -
  1. Start the engine. Hold the engine speed at 3,000 rpm (min −1 ) without load (A/T in P or N, M/T in neutral) until the radiator fan comes on, then let it idle.
  1. Check for these conditions:
    • Engine coolant temperature (ECT SENSOR 1) above 70 °C (158 °F)
    • A/T in P or N (M/T in neutral)
    • All electrical loads off
  1. Monitor the ENGINE SPEED in the DATA LIST with the HDS, and hold the engine speed at 2,500 rpm (min −1 ). Once the engine speed is met, hold the accelerator pedal steady for more than 10 seconds.
Did the engine speed vary more than 100 rpm (min −1 ) from 2,500 rpm (min −1 )?
YES -
Repeat Step 8 .
NO -
Go to Step 9 .
  1. While holding the engine speed at 2,500 rpm (min −1 ), check the MAF SENSOR in the DATA LIST with the HDS.
Is there about 4.3−5.3 gm/s (L12B1 engine) or 4.5−5.5 gm/s (L13Z1 engine) or 4.6−5.7 gm/s (L15A7 engine)?
YES -
NO -
  1. Turn the ignition switch to ON (II).
  1. Reset the ECM/PCM with the HDS.
  1. Start the engine. Hold the engine speed at 3,000 rpm (min −1 ) without load (A/T in P or N, M/T in neutral) until the radiator fan comes on, then let it idle.
  1. Test-drive under these conditions:
    • Engine coolant temperature (ECT SENSOR 1) above 70 °C (158 °F)
    • A/T in D, M/T in 4th
    • Drive at a steady speed between 24−120 km/h (15−75 mph) for 15 minutes
    NOTE: DTC P0171 and/or P0172 may take up to 80 minutes of test driving to set. Using the HDS, monitor the long term fuel trim (LT FUEL TRIM) or the air fuel feed back average (AF FB AVE). If the long term fuel trim/air fuel feed back average stays within 0.80−1.25, there is no problem at this time.
  1. Check for Temporary DTCs or DTCs with the HDS.
Is DTC P0171 or P0172 indicated?
YES -
Check for poor connections or loose terminals at the MAF sensor/IAT sensor, the injectors, the EVAP canister purge valve, and the ECM/PCM, then go to Step 1 .
NO -
Troubleshooting is complete. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC's troubleshooting.■