Circuit/System Testing: P0171: Notes

Allow the engine to reach operating temperature. With the engine running, observe the Long Term FT parameter with a scan tool. The reading should be between 0-20 percent.

If not within the specified range, 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 Versus Barometric Pressure .
- If the MAP sensor does not indicate the correct barometric pressure, refer to DTC P0106 .
With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be between 2-6 g/s at idle.
- If the MAF sensor parameter is not between 2-6 g/s at idle, refer to DTC P0101 or P1101 or DTC P0102 or P0103 .
Vacuum hoses for splits, kinks, and improper connections
Insufficient fuel in the tank
Low fuel pressure-Refer to Fuel System Diagnosis .
Ethanol concentration greater than 15 percent-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
Malfunctioning fuel injectors-Refer to Fuel Injector Diagnosis (With J39021 or With Tech 2) or Fuel Injector Diagnosis (With CH47976) .
Missing, loose, or leaking exhaust components from the HO2S forward-Refer to Symptoms - Engine Exhaust .
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
A cracked EVAP canister
Evaporative pipes obstructed or leaking
The crankcase ventilation system for leaks-Refer to Crankcase Ventilation System Inspection/Diagnosis .
The HO2S for improper 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
Malfunctioning engine components-Refer to Symptoms - Engine Mechanical .