U1812
DTC U1812
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 U1812 00
- Battery Energy Control Module Bus B High Speed Communication Enable Circuit Low
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 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 (SDG) module translates serial data messages between the high speed GMLAN serial data bus, the low speed GMLAN serial data bus, and the high speed hybrid GMLAN serial data bus. Messages between the drive motor generator battery control module and the other hybrid system control modules must pass thru the SDG module. The wake up circuit sends a voltage from the SDG module to the drive motor generator battery control module to initiate certain module functions. DTC U1812 is set by the drive motor generator battery control module, but is stored in and reported by the hybrid powertrain control module (HPCM).
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 drive motor generator battery control module did not receive voltage from the SDG module on the wake up signal circuit.
Action Taken When the DTC Sets
* The driver information center (DIC) displays the message Service Hybrid System.
* Multiple DTCs may set depending on the fault location and when the fault occurred.
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
A false DTC U1812 can set if the engine does not crank while the ignition key is held in the start position for greater than 3 seconds. Diagnose the engine does not crank condition first.
Reference Information
Schematic Reference
* Data Communication Schematics (Electrical Diagrams)
* Hybrid Controls Schematics ()
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 (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 U1862 is not set in the HPCM.
• If the DTC is set, refer to DTC U1862 (U1862).
2. Verify that DTC B137A is not set in the SDG module.
• If the DTC is set, refer to DTC B137A (B137A).
Circuit/System Testing
1. Ignition OFF, disconnect the inline harness connector X350 at the drive motor generator battery.
2. Ignition ON, verify that a test lamp illuminates between the wake up signal circuit terminal 10 X350 and ground.
• If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuit tests normal, replace the SDG module.
• If the test lamp illuminates, test the wake up signal circuit of the drive motor generator battery control module electrical harness for an open/high resistance.
3. If all circuits test normal, replace the drive motor generator battery control module.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
Control Module References (Programming and Relearning) for module replacement, setup, and programming