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

DTC P0171:  Fuel System Too Lean

NOTE: If some 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.

P0107, P0108: Manifold absolute pressure (MAP) sensor
P0133, P1157, P2195, 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
P2646, P2647, P2648, P2649: VTEC system

1.Check these parts for vacuum leaks:
  • PCV valve
  • PCV hose
  • EVAP canister purge valve
  • Throttle body
  • Intake manifold
  • Brake booster hose

Are the parts OK?

YES - Go to 2.

NO - Repair or replace parts with leaks, then go to 5.

2.Disconnect the vacuum hose (A) from the EVAP canister purge valve (B) on the throttle body, and connect a vacuum pump/gauge to the hose.


3.Apply vacuum to the hose.

Does it hold vacuum?

YES - Go to 4.

NO - Replace the EVAP canister purge valve, then go to 5.

4.Check the fuel pressure.

Is the fuel pressure OK?

YES - Check the valve clearances and adjust if necessary. If the valve clearances are OK, replace the injectors, then go to 5.

NO - Check these items:

5.Turn the ignition switch ON (II).

6.Reset the ECM/PCM with the HDS.

7.Do the ECM/PCM idle learn procedure.

8.Start the engine. Hold the engine speed at 3,000 rpm (min-1) without load (in Park or neutral) until the radiator fan comes on, then let in idle.

9.Test-drive under these conditions:
  • Engine coolant temperature more than 70 °C (158 °F)
  • A/T in D position (M/T in 5th gear)
  • Drive at a steady speed between 24-120 km/h (15-75 mph)

NOTE: DTC P0171 and/or P0172 may take up to 40 minutes of test driving to set. Using the HDS, monitor the long term fuel trim (LT FUEL TRIM) or air fuel feed back AVE (AF FB AVG) for 15 minutes of driving. If the fuel trim/AF AVE stays within 10 % of 1.0 (0.0 %), there is no problem at this time.

10.Check for Temporary DTCs or DTCs with the HDS.

Are any Temporary DTCs or DTCs indicated?

YES - If DTC P0171 or P0172 is indicated, go to 1. If any other Temporary DTCs or DTCs are indicated, go to the DTC's indicated troubleshooting.

NO - Troubleshooting is complete.n