Diagnostic Aids

WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. 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 P1639 may set in addition to DTC P1635.
For intermittent conditions, go to INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article.