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

If DTC P0172 and P0175 are set, a problem may exist in the MAF sensor circuit or the sensor may be contaminated. If the MAF sensor skews towards a higher voltage, the system will be running rich. Check sensor for signs of contamination (moisture/oil), then compare sensor voltage to a known-good vehicle under the same operating conditions.

Other possible causes if DTC P0172 and P0175 are set:

Fuel pressure high.
EVAP purge solenoid stuck open.
ECT skewed towards a lower temperature.
MAF sensor signal voltage skewed high.

Possible causes if only DTC P0172 is set:

HO2S bank 1 sensor 1 contaminated.
Fuel injector(s) leaking.
Restricted exhaust.