• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List.

Devices on the high speed GMLAN serial data bus and the chassis high speed GMLAN serial data bus must be programmed with software that specifically identifies the correct type and quantity of devices on the bus based on RPO configuration. If a device was not properly configured after installation, the appropriate U Code may be set for that device. No external circuit diagnosis is involved.

• Voltage supplied to the device is in the normal operating voltage range.
• The vehicle power mode requires serial data communication to occur.

• The device is not configured properly.
• Control unit recognises a programming error.
• CAN-Bus configuration is invalid

• A current DTC clears when the malfunction is no longer present.
• A history DTC clears when the device ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

• Data Communication Schematics
• Control Module References

Master Electrical Component List

Data Link Communications Description and Operation

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Control Module References for scan tool information

1. Ignition ON/Vehicle In Service Mode.
2. Verify DTC U18B9-U18BF is not set.
• If DTC U18B9-U18BF is set along with other DTCs set

  Diagnose all other DTCs first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle.

• If DTC U18B9-U18BF is set without other DTCs set
1. Program the device that sets the DTC.
2. Ignition/Vehicle OFF, remove the scan tool, open and close the driver door. Wait 60 s.
3. Ignition ON/Vehicle In Service Mode.
4. Verify the DTC does not set.
• If the DTC sets, replace the appropriate device.
• If the DTC does not set
5. All OK.
• If DTC U18B9-U18BF is not set
3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup