81 - Brake Switch Circuit

BRAKE SWITCH CIRCUIT-81





For a complete wiring diagram, refer to Wiring Diagram Information.

When Monitored
Ignition on.

Set Condition
Continuous brake applied signal after ignition turn-on and remaining with sensed speed above 37.5 MPH (RWAL) or 15 MPH ABS for over 10 seconds and/or ABS active for at least a second with brake switch released and never sensed brake applied since power up.

Possible Causes
- INTERMITTENT BRAKE SWITCH CIRCUIT DTC
- BRAKE SWITCH SIGNAL CIRCUIT SHORT TO VOLTAGE
- BRAKE SWITCH SIGNAL CIRCUIT OPEN
- GROUND CIRCUIT OPEN
- BRAKE LAMP SWITCH
- CAB

Diagnostic Test
1. VERIFY THE CONDITION

NOTE: Driving with the brake applied may set this code.

Turn the ignition off.
Ensure all accessories are turned off and the battery is fully charged.
Turn the ignition on.
With the scan tool, monitor the status of the brake switch while pressing and releasing the brake pedal several times.
With the scan tool, erase DTCs.

CAUTION: Determine that braking capability is available before road testing the vehicle. Road test the vehicle for at least 5 minutes over 40 MPH. Perform several anti-lock braking stops. With the scan tool, read DTCs.

Does the original DTC reset and/or does intermittent brake switch operation occur?
Yes >> Go To 2
No >> The condition necessary to set this DTC is not present at this time. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors relative to this circuit.
Perform ABS VERIFICATION TEST - VER 1. ABS Verification Test

2. BRAKE LAMP SWITCH
Turn ignition off.
Disconnect the Brake Lamp Switch harness connector.
Turn ignition on.
With the scan tool, monitor the brake switch status.
Connect and disconnect a jumper wire between the Ground circuit and the Brake Switch Signal circuit.

Does the scan tool display correctly with the jumper wire connected and disconnected?
Yes >> Replace the Brake Lamp Switch in accordance with the Service Information.
No >> Go To 3

3. BRAKE SWITCH SIGNAL CIRCUIT SHORT TO VOLTAGE





Turn the ignition off.
Disconnect the CAB Module harness connector.
Turn the ignition on.
Measure the voltage of the Brake Switch Signal circuit.

Is there any voltage present?
Yes >> Repair the Brake Switch Signal circuit for a short to voltage.
Perform ABS VERIFICATION TEST - VER 1. ABS Verification Test
No >> Go To 4

4. BRAKE SWITCH SIGNAL CIRCUIT OPEN





Turn the ignition off.
Measure the resistance of the Brake Switch Signal circuit between the CAB harness connector and the brake switch harness connector.

Is the resistance above 5.0 ohms?
Yes >> Repair the open Brake Switch Signal circuit.
Perform ABS VERIFICATION TEST - VER 1. ABS Verification Test
No >> Go To 5

5. GROUND CIRCUIT OPEN





Using a 12-volt test light connected to 12 volts, check the Ground circuit at the brake switch harness connector.

NOTE: The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.

Is the test light illuminated and bright?
Yes >> Replace the Controller Anti-lock in accordance with the Service Information. Refer to the symptom *Replacing the Controller Anti-lock Brake.
Perform ABS VERIFICATION TEST - VER 1. ABS Verification Test
No >> Repair the Ground circuit for an open circuit or high resistance.
Perform ABS VERIFICATION TEST - VER 1. ABS Verification Test