C1091 Code | ABS Brake Lamp Control Circuit High
July 18, 2018
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C1091 Code - the Electronic Stability Control (ESC) may also be refferd to as Electronic Stability Program (ESP) depending on the vehicle model year and configuration. Certain components may also reference ESP, ESC, or use the traction symbol. When monitoring the brake lamp relay control circuit the module detects a short to B+
Possible causes C1090 Code
- Brake lamp activation relay control shorted to voltage
- Brake lamp activation relay
- Antilock Brake System (ABS) Module
Diagnose C1091 Code
Step 1. Check for DTC C1091 ABS BRAKE LAMP CONTROL CIRCUIT HIGH
This DTC must be active for the result 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: C1091 ABS BRAKE LAMP CONTROL CIRCUIT HIGH?
Yes, go to step 2.
No, go to ABS Intermittent condition.
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 connector/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 12-volt test light connected 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.
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 connector/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 12-volt test light connected 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.
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