U182A
DTC U182A
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
DTC Descriptor
DTC U182A 00
- Lost Communication With Battery Energy Control Module on Bus B
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 volts.
* The ignition in RUN.
Conditions for Setting the DTC
* The APM wake up signal is open.
* The APM does not receive battery voltage.
* The PTLAN 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 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
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 Views)
Description and Operation
Data Link Communications Description and Operation (Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Circuit/System Verification
With a scan tool, 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 Descriptions) to diagnose that DTC prior to this diagnostic.
Circuit/System Testing
1. Ignition OFF, disconnect harness connector X1 of the APM.
2. Ignition ON, test for B+ between the wake up signal circuit terminal C and ground.
• If less than the specified value, test the circuit for an open/high resistance. If the circuit tests normal, replace the SDGM.
3. Ignition OFF, disconnect harness connector X3 of the APM.
4. Ignition ON, test for B+ between the B+ circuit terminal A and ground.
• If less than the specified value, test the circuit for an open/high resistance. If the circuit tests normal, replace the SDGM.
5. Disconnect harness connector X1 of the EBCM.
6. Test for less than 1.0 ohm between the APM and the EBCM on the following circuit terminals.
* PTLAN + APM terminal 5 and EBCM terminal 33
* PTLAN - APM terminal 4 and EBCM terminal 21
• If greater than the specified range, test the circuit for an open/high resistance.
7. Ignition OFF, disconnect harness connector X1 of the SDGM.
8. Test for less than 1.0 ohm between the EBCM and the SDGM on the following circuit terminals.
* PTLAN + EBCM terminal 34 and SDGM terminal 14
* PTLAN - EBCM terminal 22 and SDGM terminal 12
• If greater than the specified range, test the circuit for an open/high resistance.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* GMLAN Wiring Repairs (Component Tests and General Diagnostics)
* Control Module References (Programming and Relearning)for module replacement, setup, and programming