Diagnostic Instructions

DTC Descriptors

DTC U0140 00: Lost Communication With Body Control Module

DTC U0184 00: Lost Communication With Radio

DTC U0194 00: Lost Communication With Digital Audio Control Module B

DTC U0198 00: Lost Communication With Telematic Control Module

Circuit/System Description

Modules connected to the high and low speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.

The body control module (BCM) activates the serial data communication enable circuit by applying voltage when the ignition key is in ACC, ON or START. The serial data communication enable circuit wakes up the electronic brake control module (EBCM), all wheel drive module, and the electronic power steering control module if equipped for buss communication.

Conditions for Running the DTC

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

Conditions for Clearing the DTC

Reference Information

Schematic Reference

Connector End View Reference

Component Connector End Views

Electrical Information Reference

Circuit/System Testing

1. Using the DTC Descriptor and Diagnostic Aids above, determine the module that is not communicating that should be tested.
2. Ignition OFF, disconnect the harness connector of the module that is not communicating.

Important: Only the high speed GMLAN modules have a the serial data communication enable circuit. Refer to the module schematics to identify which modules have these circuits. If the module that is not communicating does not have one of these circuits, proceed to step 4.

3. Ignition ON, verify that a test lamp illuminates between the serial data communication enable circuit and ground.

⇒	If the test lamp does not illuminate, repair the circuit for an open/high resistance. If the circuits test normal, replace the BCM.

4. Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground.

⇒	If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module.

5. Verify that a test lamp illuminates between all ignition voltage circuits and ground.

⇒	If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module.

6. Test for less than 1 ohm of resistance between the module ground circuits and ground.

⇒	If greater than 1 ohm, repair the ground circuit for an open.

7. Use Data Link References to determine if the non-communicating module should use low speed GMLAN serial data.

⇒	If the module is GMLAN high speed only, replace the module.

8. Test for less than 1 ohm of resistance in the low speed GMLAN serial data circuit between the non-communicating module and the module that displays the DTC.

⇒	If greater than 1 ohm of resistance, test the low speed GMLAN serial data circuit for open/high resistance.

9. If all circuits test normal, replace the module that is not communicating.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for replacement, setup, and programming