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.
P0068, P0106, P0107, P0108: Manifold absolute pressure (MAP) sensor
P0130, P0132, P0134: Primary HO2S sensor (Sensor 1)
P0135: Primary HO2S sensor (Sensor 1) heater
P0137, P0138, P0140: Secondary HO2S (Sensor 2)
P0141: Secondary HO2S (Sensor 2) heater
P0201-P0204, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271: Injector
P0401, P0403, P0404, P0405, P0406, P0409, P0489, P0490: Exhaust gas recalculation (EGR) system
P0444, P0445: EVAP canister purge valve

1.Check the following parts for vacuum leaks:
  • PCV valve
  • PCV hose
  • EVAP canister purge valve
  • Throttle body
  • Brake booster hose

Are they OK?

YES - Go to 2.

NO - Repair or replace parts for vacuum leaks, then go to 10.

2.Check the fuel pressure.

Is the fuel pressure OK?

YES - Go to 3.

NO - Check these items:

3.Turn the ignition switch OFF.

4.Disconnect the vacuum hose (A) and connect a vacuum gauge (B) to the hose.


5.Apply vacuum to the EVAP canister purge valve (C).

Does it hold vacuum?

YES - Go to 6.

NO - Replace the EVAP canister purge valve, then go to 10.

6.Turn the ignition switch ON (II).

7.Check the MAP SENSOR in the DATA LIST with the HDS.

Is atmospheric pressure indicated?

YES - Go to 8.

NO - Replace the IAT/MAP sensor, then go to 10.

8.Start the engine.

9.Check the MAP SENSOR in the DATA LIST with the HDS.

Is about 46.6 kPa (350 mmHg, 13.7 in.Hg) indicated within 1 second after starting the engine?

YES - Check the valve clearances and adjust if necessary. If the valve clearances are OK, replace the injectors, then go to 10.

NO - Replace the IAT/MAP sensor, then go to 10.

10.Turn the ignition switch ON (II).

11.Do the ECM RESET in the CLEAR MENU with the HDS.

12.Do the ETCS learn procedure.

13.Start the engine. Hold the engine speed at 3,000 rpm (min-1) with no load (in neutral) until the radiator fan comes on, then let it idle.

14.Test-drive under following conditions.
  • Engine Coolant temperature more than 70°C (158°F)
  • Transmission in 5th gear
  • Drive at a steady speed between 60-80 km/h (38-50 mph) for 40 minutes

15.Check for Temporary DTCs or DTCs in the DTCs MENU 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 indicated DTC troubleshooting.

NO - Troubleshooting is complete.n