Circuit/System Testing For DTC P0171
- Allow the engine to reach operating temperature. With the engine running, observe the Long Term FT parameter with a scan tool. The value should be less than approximately 19.5 percent with the engine running at operating temperature.
- If the value is not less than 19.5 percent, inspect for the following:
- With the ignition ON and the engine OFF, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor pressure should be within the range specified for your altitude. Refer to Altitude vs Barometric Pressure
.
- Vacuum hoses for splits, kinks, and proper connections
- Sufficient fuel in the tank
- Low fuel pressure
- Fuel contamination
- Properly functioning fuel injectors
- Missing, loose, or leaking exhaust components from the HO2S forward
- Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings
- The air induction system and the air intake ducts for leaks or for a missing air filter element
- Evaporative canister purge lines plugged or obstructed
- The crankcase ventilation system for leaks
- The HO2S for proper installation and for electrical wires or connectors that may have contacted the exhaust system
- The HO2S signal circuit open, shorted to ground, or shorted to the low reference circuit
- The HO2S sensor 1 low signal circuit for an open circuit or high resistance
- Malfunctioning engine components