Diagnostic Aids
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 Chevrolet Tahoe, 2003 Chevrolet Suburban, and 2003 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
Important: Do not clear DTCs unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable Freeze Frame and Failure Records data.
- If the powertrain control module (PCM) is replaced, the PCM must re-learn a valid password and crankshaft variation.
- If the body control module (BCM) is replaced, the PCM must re-learn a valid password.
- Check for published service bulletins relating to exhibited symptoms or component operation.
- If the vehicle does not start, or starts and stalls:
- Turn OFF the ignition and wait at least 5 seconds before trying to restart.
- If a fault or tamper has been detected, the BCM will not forward the correct password to the PCM for a period of ten minutes, even if the condition is corrected during that time period. This may cause a DTC P1631 to set in the PCM. This timer can be monitored in the Passlock Data parameter of the scan tool. Once the time has elapsed, the BCM will determine if the condition is still present.
- The PCM and BCM parameters can be monitored with a scan tool.
- The Passlock state and the auto learn timer can be viewed in the Passlock Data parameter of the scan tool.
- Check the following for preventing the Passlock sensor from communicating with the BCM:
- Passlock sensor
- Ignition switch assembly
- Passlock sensor circuitry
- Bent pins at the small Passlock sensor
- If this DTC sets along with a DTC B2960, then the problem was caused by malfunctioning Passlock components or circuitry, not the PCM.
- Inspect all related wiring and connections including the PCM and BCM 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 the intermittent complaint. Refer to TESTING WIRING SYSTEMS FOR INTERMITTENT & POOR CONNECTIONS in Wiring Systems.
If a repair is necessary, Refer to WIRING REPAIRS or CONNECTOR REPAIRS in Wiring Systems.