Diagnostic Aids
WARNING: This page is about a different car, the 2003 Pontiac Aztek and 2003 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.
If any sensor using a 5-volt bias voltage, such as the Intake Air Temperature (IAT) sensor or fuel sensor is shorted to voltage, DTC P1635 may set in addition to DTC P1639. For an intermittent condition, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 3.4L AZTEK & RENDEZVOUS article.