U182A
DTC U182A
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 Descriptor
DTC U182A 00
- Lost Communication With Accessory Power Module
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 serial data gateway module (SDGM) energizes the wake up signal to activate the accessory DC power control module (APM) when communication is needed. The SDGM monitors the signal circuit for faults.
Conditions for Running the DTC
* The system voltage is between 9-16 V.
* The ignition in RUN.
Conditions for Setting the DTC
* The APM wake up signal is open.
* The APM does not receive battery voltage.
* The powertrain serial data circuits between the SDGM and the APM are open.
Action Taken When the DTC Sets
The modules is never signaled, therefore the specific subsystems may not function. Depending on the fault, the MIL, battery indicator may illuminate and several DIC messages may be present.
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.
Diagnostic Aids
* When testing circuits to the SDGM access can be accomplished by removing the instrument panel center trim panel. Note that this procedure does not allow removal of the SDGM, only access to the connector. Refer to Instrument Panel Center Trim Panel Replacement .
* Different DTCs may set in different modules along with this DTC depending on where the fault occurs and the vehicle operating conditions when the fault occurs.
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
1. Verify that DTC B137B or U189A are not present in the SDGM.
• If any listed DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle to diagnose that DTC prior to this diagnostic.
2. Verify the DTC U0074 is not set.
• If DTC U0074 is set as a current or history code, refer to DTC U0074 U0074.
Circuit/System Testing
1. Ignition OFF, test for less than 1.0 ohm between the accessory DC power control module case and ground strap.
• If greater than the specified value, test the ground circuit for an open/high resistance.
2. Disconnect harness connector X3 of the accessory DC power control module.
3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal A and ground.
• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. If the circuit fuse is open, test the control circuits of the accessory DC power control module for a short to ground.
4. Ignition OFF, disconnect harness connector X1 of the accessory DC power control module.
5. 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 wake up signal circuit for an open/high resistance or a short to ground. If the circuit tests normal, replace the serial data gateway module.
6. If all circuits test normal, replace the accessory DC power control module.
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 control module replacement, setup, and programming