C0800

DTC C0800

Diagnostic Instructions

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

DTC Descriptor
DTC C800 03
- Device Power Circuit Voltage Below Threshold

DTC C800 07
- Device Power Circuit Voltage Above Threshold

Circuit/System Description

The trailer brake control module (TBCM) monitors the system voltage (ignition voltage) to make sure that the voltage stays within the proper range. Damage to components, and incorrect data input can occur when the voltage is out of range. The TBCM monitors the system voltage over an extended length of time. If the TBCM detects a system voltage outside an expected range, DTC C0800 will set.

Conditions for Running the DTC

* The ignition is ON.
* The engine speed is greater than 400 RPM.

Conditions for Setting the DTC

C0800 03
* During initialization or when the system is inactive, the system voltage is less than 10.5 volts.
* During the system operation, the system voltage is less than 9.5 volts.

C0800 07
* Ignition is in RUN.
* The system voltage is greater than 17 volts.

Action Taken When the DTC Sets

* The trailer brake control will be disabled at the end of the current brake apply 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

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

C0800 03
* Test the charging system. Refer to Diagnostic System Check - Vehicle. Initial Inspection and Diagnostic Overview
* Possible causes of this DTC are the following conditions:

- A charging system malfunction
- An excessive battery draw
- A weak battery
- A faulty system ground

C0800 07
* Test the charging system. Refer to Diagnostic System Check - Vehicle. Initial Inspection and Diagnostic Overview
* A possible cause of this DTC is overcharging.

Circuit/System Verification

With the scan tool installed, ignition ON and the engine running, observe the Battery Positive Voltage parameter in the TBCM data list. The reading should be between 9-17 volts.

Circuit/System Testing

1. If the DTC is history, refer to Charging System Test. Charging System Test
2. If the DTC is current, start the engine, and measure the voltage between the battery positive voltage circuits of the TBCM and the ground circuit.

* If the voltage is within 9-17 volts, replace the affected module.
* If the voltage is not within 9-17 volts, measure the voltage between the battery positive voltage circuits of the TBCM and a separate good ground.
* If the voltage is within 9-17 volts, test the battery positive ground circuits of the TBCM for high resistance or an open, and repair as necessary.

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