C0845

DTC C0845

Diagnostic Instructions

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

DTC Descriptor
DTC C0845 03
- Device Ignition 1 Circuit Voltage Below Threshold

Diagnostic Fault Information





Circuit/System Description

The trailer brake control module (TBCM) checks whether there is an ignition ground short fault. This diagnostic compares ignition state with the engine running state received over serial data to determine whether or not there is an ignition ground short fault.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

The engine is running, and the TBCM detects that the IGN 1 voltage is less than 9.2 volts

Action Taken When the DTC Sets

* The trailer brake control will be disabled for the remainder of the ignition cycle.
* The Service Trailer Brake System will be displayed on the Driver Information Center (DIC).

Conditions for Clearing the MIL/DTC

* When the condition for the DTC is no longer present.
* The TBCM automatically clears the history DTC when a current DTC is not detected in 40 consecutive drive cycles.

Diagnostic Aids

Important: The ignition may need to be cycled twice, waiting 30 seconds between key cycles, to move the code from current to history

If there are any other DTCs set for GMLAN communication such as U0100, U0121, U0140, or U2099, diagnose them first before resolving DTCs described in this section.


Circuit/System Testing

Important: Verify that stop lamp DTCs are not set as current or history before performing this diagnostic. If stop lamp DTCs are set as current or history, go to lighting for diagnose.

1. Ignition OFF, disconnect the harness connector of the TBCM.
2. Ignition ON, test for 11 volts or greater between the IGN 1 voltage circuit terminal 15 and ground.

* If less than the specified voltage, test the IGN 1 voltage circuit for a short to ground or an open/high resistance. If the circuit test normal and the MISC - IGN fuse 44 (Gas) or 41 (Diesel) is open, test the voltage circuit for a short to ground. If the circuit tests normal, test or replace the RUN/CRANK relay.

3. If all circuits test normal, and the DTC resets as current, replace the TBCM.

Repair Instructions

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

Refer to Programming and Relearning for TBCM setup and programming. Programming and Relearning