Diagnostic Aids

• Check for published service bulletins relating to exhibited symptoms or component operation.
• Inspect all related wiring and connections including the powertrain control module (PCM) and body control module (BCM) connections. These may cause an intermittent malfunction.
• If the Class 2 Serial Data circuit is shorted to ground or shorted to voltage, then all systems connected to the serial data circuit will not be able to communicate properly. Systems capable of storing loss of communications DTCs, or the DTCs with the letter "U" as a prefix, will have these codes stored in their memory. If a DTC U1192 is stored in the PCM memory along with the P1626, then a fault occurred at some point after the PCM received the correct password. The BCM must also be checked for intermittent operation due to a loss of power or ground to the module itself. After repairing the cause of DTC 1626, clear all DTCs from the systems capable of storing this DTC and DTC U1192.
• The VTD Passlock parameters can be monitored in the PCM under engine data 2, display with a scan tool.
• The 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 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.
• The scan tool Class 2 Message Monitor will show the status of each module on the Class 2 circuit. A status of Active indicates that the module is communicating with the scan tool. An Inactive status indicates that the module previously communicated with the scan tool, but is not communicating currently. The inactive status will only appear if the loss of communication occurs while on the Message Monitor screen. If a module is not listed at all, then the missing module never successfully established communications with the scan tool or lost communication while on another screen. Refer to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications for the complete Class 2 data link to determine if there are any unlisted modules.

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 for Intermittent Conditions and Poor Connections in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.