DTC P0171 & P0172: Fuel System Too Rich Or Too Lean
NOTE:
DTC P0171 indicates fuel system is too lean. DTC P0172 indicates fuel system is too rich. If DTCs P0106, P0107, P0108, P0135, P0137, P0138, P0141, P0441 or P1259 is set, trouble shoot those DTCs before trouble shooting DTCs P0171 and/or P0172.
- If DTC P0171 (system to lean) is set, check for:
- Insufficient fuel pump flow or pressure.
- Clogged or leaking fuel feed line.
- Fuel pressure regulator stuck open.
- Clogged fuel filter.
- Clogged or air blocked fuel injector.
- Fuel octane level less than specification.
- A deteriorated HO2S-1.
- Proper MAP sensor range and/or performance.
- Proper valve adjustment.
- An exhaust leak.
Repair as necessary. If no problems are found, go to step 3).
- If DTC P0172 (system to rich) is set, check for:
- Fuel pressure regulator clogged or stuck closed.
- Clogged fuel return line.
- A leaking fuel injector.
- Fuel octane level less than specification.
- A deteriorated HO2S-1.
- Proper MAP sensor range and/or performance.
- A leaking or stuck open EVAP purge control solenoid valve.
- Valve adjustment to loose.
Repair as necessary. If no problems are found, go to next step.
- Check fuel pressure. See FUEL SYSTEM in the BASIC TESTING - GS-R article. If fuel pressure is okay, go to next step. If fuel pressure is too high, check fuel pressure regulator and fuel return line. Repair as necessary. If fuel pressure is too low, check fuel pump, fuel feed line, fuel filter and fuel pressure regulator. Repair as necessary.
- Start engine and run at 3000 RPM with no loads and transmission in Park or Neutral, until radiator fan comes on. Using scan tool, check HO2S-1 output voltage. If voltage does not stay at less than 0.3 volt or more than 0.6 volt, go to next step. If voltage stays at less than 0.3 volt or more than 0.6 volt, replace HO2S-1.
- Using vacuum pump, apply vacuum to EVAP purge control solenoid valve from intake manifold side. If vacuum holds, go to next step. If vacuum does not hold, replace EVAP purge control solenoid valve.
- Turn ignition on. Using scan tool, check MAP sensor data. If atmospheric pressure is not present, replace MAP sensor. If atmospheric pressure is present, start engine and check MAP sensor data. If MAP data is 12.0 in. Hg (40.0 kPa) or less within one second of engine start, replace MAP sensor. If MAP data is not 12.0 in. Hg (40.0 kPa) or less within one second, check valve clearance. If valve clearance is okay, replace fuel injectors.