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.

If any TP sensor 1 or 2 DTC is set, diagnose that DTC first.

If DTC P0638 is set, the ECM will default to one of the two limp home modes (random injector disable with engine speed limited to 2600 RPM). The REDUCED POWER telltale will be illuminated and the ECM will remain in this condition for the entire ignition cycle even if the fault is corrected.

To locate an intermittent problem, use scan tool to monitor DTC P0638 LAST TEST while accelerating the engine up and down the RPM band. When fault occurs, the parameter will change from PASSED to FAILED. THROTTLE ACTUATOR DC on scan tool will remain at 99 percent if any fault is occurring as well. This parameter will normally fluctuate between 0 and 99 percent.

A binding throttle plate can set this DTC. Turn ignition off, remove the air induction tubing and disconnect the TAC module. Move the throttle plate by hand to the full open and full closed position to check for a sticking or binding condition.