C1091 ABS Brake Lamp Control Circuit High


C1091 ABS Brake Lamp Control Circuit High


When monitoring the brake lamp activation relay control circuit the module detecsts a short to B+


Possible causes code C1091 ABS Brake Lamp Control Circuit High

  • Brake lamp activation relay control shorted to voltage
  • Brake lamp activation relay.
  • Antilock Brake System (ABS) Module.


How to fix diagnose code C1091 ABS Brake Lamp Control Circuit High


Step 1. Check for DTC C1091 ABS brake lamp control circuit high

This DTC must be active for the results of this test to be valid
Turn the ignition on, with the scan tool record and erase the DTCs. Start the engine, apply the brake pedal firmly with at least 80 bar (1160 psi). With the scan tool read the DTCs.

Does the scan tool display code C1091?

YES, go to step 2.
NO, perform the ABS Module intermittent.

Step 2. Check connector/terminal for damage

Check all terminals for broken, bent, pushed out or corroded terminals.
Turn the ignition off, inspect the ABS Module harness connector and the brake lamp activation relay harness connector.

Is the ABS Module or any of the connectors/terminals damaged?

YES, repair as necessary.
NO, go to step 3.

Step 3. Brake lamp activation relay control shorted to voltage

Turn the ignition off, disconnect the ABS Module harness connector. Disconnect the brake lamp activation relay harness connector. Turn the ignition on, using a 12volt test light conencted to ground, probe the brake lamp activation relay control circuit at the brake lamp activation relay harness connector.

Does the test light illuminate brightly?

YES, repair the short to voltage in the brake lamp activation relay control circuit.
NO, go to step 4.

Step 4. Brake lamp activation relay

Turn the ignition off, measure the resistance across the relay between the brake lamp activation relay control circuit and the fused run/start relay output.

Is the resistance 75 Ohms ± 5 Ohms?

YES, replace the Antilock Brake System (ABS) Module. Perform the ABS verification test.
NO, replace the brake lamp activation relay.

Test complete for code C1091 ABS Brake Lamp Control Circuit High.

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