B3894

DTC B3894 (Gasoline With LY6, or Diesel)

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) provide an overview of each diagnostic category.

DTC Descriptor
DTC B3894 5A
- Stop Lamp Switch Circuit Plausibility Failure

Circuit/System Description

The brake switch is hard wired to the trailer brake control module (TBCM). The body control module (BCM) sends a brake switch status serial data message to the trailer brake control module. The trailer brake control module compares the states of the brake switch signal to the serial data message after a master cylinder brake pressure sensor threshold is exceeded. If the brake switch signal and the serial data message are not in agreement or if the serial data message is not valid, a DTC will set and the trailer brake control system will be disabled.

Conditions for Running the DTC

* Battery voltage is 9.5-17 V.
* The module initialization has taken place.
* The master cylinder brake pressure exceeds threshold

Conditions for Setting the DTC

* The brake switch serial data message is not valid.
* The actual brake switch input to the trailer brake control module, and the serial data information for the brake switch do not match.

Action Taken When the DTC Sets

* The trailer brake control will be disabled for the remainder of the ignition cycle.
* The driver information center 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 ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Trailer Brake Controls Description and Operation (Trailer Brake Controls)
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)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

Ignition ON, press the brake pedal. The brake lights should illuminate and the Brake Switch Status parameter should indicate ON.

Circuit/System Testing

1. Verify that DTC B3445, C0277, C0297, or C0890 are not set.

• If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle).

2. Ignition OFF, disconnect the harness connector of the trailer brake control module.
3. Ignition ON, test for greater than 11 V 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 is open, test the signal circuit terminal 37 for a short to ground. If the circuit tests normal, test or replace the RUN/CRANK relay.

4. If all the circuits test normal, replace the trailer brake control module.

Repair Instructions

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

* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Control Module References (Programming and Relearning) for TBCM replacement, setup, and programming