Diagnostic Aids

WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

Diagnose any ECT, fuel injector, IAT, heated oxygen sensor, MAF, MAP or TP sensor DTCs first.

The ECM will only update the long term fuel trim bank 1 value (LT FT BN. 1 CRUISE/ACCEL. parameter on scan tool) when:

ECT is greater than 140°F (60°C).
Volumetric efficiency is 24-70 percent.
MAF is between 15.20 and 64.72 g/s.

Use LT FT BN. 1 IDLE/DECEL. parameter on scan tool to verify the system is running lean at idle (greater than 8.1 percent) or LT FT BN. 1 CRUISE/ACCEL within the criteria to verify the system is running lean during cruise (greater than 23 percent).

If DTC P0171 and P0174 are set, a problem may exist in the MAF sensor circuit. If the MAF sensor skews towards a lower voltage, the system will be running lean. Compare sensor voltage to a known-good vehicle under the same operating conditions.

Other possible causes if DTC P0171 and P0174 are set:

Vacuum leak.
Fuel pressure low.
Fuel quality poor or water in fuel.
ECT skewed towards a higher temperature.
MAF sensor signal voltage skewed low.

Possible causes if only DTC P0171 is set:

Vacuum leak.
Fuel injectors clogged.
Exhaust manifold gasket leak around the HO2S bank 1 sensor 1.