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 Class 2 Serial Data circuit is shorted to ground or shorted to voltage, then all systems connected to serial data circuit will not be able to communicate properly. Systems capable of storing loss of communications DTCs, or DTCs which begin with a "U", will have these codes stored in their memory. If a DTC U1192 is stored in PCM memory along with P1626, then a fault occurred at some point after PCM received the correct password. Theft system must also be checked for intermittent operation due to a loss of power or ground to module itself. After repairing cause of DTC P1626, clear all DTCs from systems capable of storing this DTC and DTC U1192. Passlock(tm) module parameters can be monitored in PCM data display with a scan tool. Scan tool Diagnostic Circuit Check can be used to:
- Monitor the Class 2 Serial Data circuit for modules which have been or are communicating.
- Monitor for loss of communications DTCs (DTCs with the letter "U" as a prefix: U1001-U1199).
- Clear loss of communication DTCs. When a Clear Codes command is issued, all codes, freeze frame and failure records information is cleared.
Scan tool Class 2 Message Monitor will show status of each module on Class 2 circuit. A status of ACTIVE indicates module is communicating with scan tool. An INACTIVE status indicates module previously communicated with scan tool, but is not currently communicating. Inactive status will only appear if loss of communication occurs while on message monitor screen. If a module is not listed at all, then missing module never successfully established communications with scan tool or lost communication while on another screen. Go to
TEST B: SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE
in BODY CONTROL MODULES - CHEVY EXPRESS & SAVANA article. An intermittent may be caused by any of the following conditions:
- A poor connection.
- Rubbed through wire insulation.
- A broken wire inside insulation.
Thoroughly inspect any circuitry suspected of causing intermittent complaint. If DTC is a history DTC, problem may be intermittent. Perform tests while wiggling wiring.