GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2009 🢒 Yukon Denali 🢒 DTC 🢒 DTC C0800

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provide an overview of each diagnostic category.

DTC Descriptor

DTC C0800 03 : Device Power Circuit Voltage Below Threshold

DTC C0800 07: Device Power Circuit Voltage Above Threshold

Circuit/System Description

The trailer brake control module (TBCM) monitors the battery voltage. Damage to components, and incorrect data input can occur when the voltage is out of range.

Conditions for Running the DTC

Engine running.

Conditions for Setting the DTC

C0800 03

During the system operation, the system voltage is less than 9.5 volts.

C0800 07

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 driver information center (DIC) will display Service Trailer Brake System.

Conditions for Clearing the DTC
    • The condition for the DTC is no longer present.
    • The TBCM clears the history DTC when a current DTC is not detected in 40 consecutive drive cycles.

Reference Information

Schematic Reference

Trailer Brake Control Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Trailer Brake Controls Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Engine running, observe the scan tool TBCM Battery Voltage Signal parameter. The reading should be between 12.6 and 15.0 volts.

Circuit/System Testing
  1. Engine running, accessories OFF, measure the battery voltage at the battery terminals. The voltage should be between 12.6 and 15.0 volts.
    2. ⇒If not within the specified range, refer to Charging System Test.
  2. Ignition OFF, disconnect the harness connector at the TBCM.
  3. Ignition OFF, test for less than 5 ohms between the ground circuit terminal 1 and ground.
    4. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  4. Verify that a test lamp illuminates between the B+ circuit terminal 32 and ground.
    5. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  5. If all circuits test normal, replace the TBCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for TBCM replacement, setup, and programming