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

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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

* Exterior Lights Schematics Exterior Lights Schematics

Connector End View Reference

Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)

Description and Operation

Trailer Brake Controls 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

Scan Tool Reference

Control Module References Control Module References 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

Note:
Diagnose all other brake light DTCs or Symptoms prior to performing this diagnostic procedure.

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 at the trailer brake control module.

3. Ignition ON, test for greater than 11 V between the ignition circuit terminal 15 and ground.

• If less than the specified range, test the ignition 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.

4. Ignition OFF, disconnect the harness at the stop lamp switch.

5. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal B and ground.

• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

6. Ignition OFF, connect the harness connector at the stop lamp switch.

7. Connect a test lamp between the signal circuit terminal 37 of the trailer brake control module harness connector and ground.

8. Ignition ON, apply and release the brake pedal, the test lamp should turn ON and OFF when applying and releasing the brake pedal.

• If the test lamp is always ON, test the signal circuit for a short to voltage. If the circuit tests normal, test or replace the stop lamp switch.

• If the test lamp is always OFF, test the signal circuit for an open/high resistance. If the circuit tests normal, test or replace the stop lamp switch.

9. Ignition OFF, disconnect the X5 harness connector at the body control module (BCM).

10. Ignition ON, verify a test lamp illuminates between the signal circuit terminal 5 and ground with the brake pedal applied.

• If the test lamp does not illuminate, test the signal circuit for an open/high resistance.

11. 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 (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)

* Control Module References Control Module References for TBCM replacement, programming and setup