Diagnostic Aids

WARNING: This page is about a different car, the 2002 GMC Savana, 2002 Chevrolet Chevy Express, 2001 GMC Savana, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Do not clear DTCs unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable Freeze Frame and Failure Records data.

If PCM is replaced, PCM must relearn a valid password and crankshaft variation. If Passlock(tm) module is replaced, PCM must relearn a valid password. Check for published service bulletins relating to exhibited symptoms or component operation. If vehicle does not start, or starts and stalls, turn ignition switch to OFF position and wait at least 5 seconds before trying to restart. If a fault or tamper has been detected, Passlock(tm) module will not forward the correct password to PCM for a period of ten minutes, even if condition is corrected during that time period. This may cause a DTC P1631 to set in PCM. This timer can be monitored in Passlock(tm) data parameter of the scan tool. Once time has elapsed, Passlock(tm) module will determine if condition still exists. PCM Passlock(tm) parameters can be monitored with a scan tool. Passlock(tm) state and auto learn timer can be viewed in Passlock(tm) Data parameter of scan tool. Check the following for preventing Passlock sensor from communicating with Passlock module:

Passlock(tm) sensor.
Ignition switch assembly.
Passlock(tm) sensor circuitry.
Bent pins at the small Passlock(tm) sensor.

If DTC P1631 sets along with a DTC B2960, then problem was caused by malfunctioning Passlock(tm) components or circuitry, not the PCM. Inspect all related wiring and connections including PCM and Passlock(tm) module connections. These may cause an intermittent malfunction. An intermittent may be caused by any of the following conditions:

A poor connection.
Rubbed through wire insulation.
A broken wire inside the insulation.

Thoroughly inspect any circuitry that is suspected of causing intermittent complaint.