B137B

DTC B137B

Diagnostic Instructions

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

DTC Descriptors
DTC B137B 06
- Accessory Power Module Wake Up Circuit - short to ground or open

Diagnostic Fault Information






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 wake up signal circuit is energized by the serial data gateway module (SDGM) to activate the accessory DC power control module (APM) immediately when the body control module (BCM) signals the SDGM that serial data is required.

Conditions for Running the DTC

* The system voltage is between 9-16 volts.
* The vehicle power mode master requires serial data communication to occur.

Conditions for Setting the DTC

The wake up signal circuit is shorted to ground.

Action Taken When the DTC Sets

The module is never signaled and the charging system will not operate. The battery indicator will illuminate along with multiple driver information messages.

Conditions for Clearing the DTC

* A current DTC clears when the malfunction is no longer present.
* A history DTC clears when the module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Reference Information
Schematic Reference

* Data Communication Schematics Electrical Diagrams
* Control Module References Programming and Relearning

Connector End View Reference

Component Connector End Views Connector End Views By Name
Description and Operation

Data Link Communications Description and Operation Description and Operation
Electrical Information Reference

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

Circuit/System Verification

With a scan tool, verify that DTC U182A is not set in the SDGM, and U189A is not set in the HPCM.

If either DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector X1 at the APM.
2. Ignition ON, verify that a test lamp illuminates between the wake up signal circuit terminal 3 and ground.

• If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance.

3. Ignition OFF and scan tool disconnected, verify that a test lamp does not illuminate between the signal circuit terminal 3 and ground.

• If the test lamp illuminates, test the circuit for a short to voltage.

4. If all circuits test normal, replace the APM.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* GMLAN Wiring Repairs GMLAN Wiring Repairs
* Control Module References Programming and Relearningfor module replacement, setup, and programming