C1291

CIRCUIT DESCRIPTION
Diagnostic Trouble Code (DTC) C1291 detects an open brake switch. The Electronic Brake Control Module (EBCM) looks for deceleration rates that may indicate braking action. The EBCM verifies braking action by repeating the method for finding deceleration rates that indicate braking action several times. In each case, the ABS will not be available because the EBCM does not see the brake switch input.

CONDITIONS FOR SETTING THE DTC
^ Diagnostic Trouble Code (DTC) C1291 can set if three deceleration cycles within the specified rate occur during the current ignition cycle with the brake switch off.

ACTION TAKEN WHEN THE DTC SETS
^ A malfunction Diagnostic Trouble Code (DTC) stores.
^ The ABS disables.
^ The ABS warning indicator turns ON.

CONDITIONS FOR CLEARING THE DTC
^ The condition responsible for setting the Diagnostic Trouble Code (DTC) no longer exists and the Scan Tool Clear DTCs function is used.
^ 100 drive cycles pass with no DTCs detected. A drive cycle consists of starting the vehicle, driving the vehicle over 16 km/h (10 mph), stopping and then turning the ignition OFF.

DIAGNOSTIC AIDS
The following conditions may cause an intermittent malfunction:
^ A poor connection
^ Rubbed-through wire insulation
^ A broken wire inside the insulation

Use the enhanced diagnostic function of the Scan Tool in order to measure the frequency of the malfunction.
Thoroughly inspect any circuitry that may cause the intermittent complaint for the following conditions:
^ Backed out terminals
^ Improper mating
^ Broken locks
^ Improperly formed or damaged terminals
^ Poor terminal-to-wiring connections
^ Physical damage to the wiring harness
^ Sticking brake switch

TEST DESCRIPTION
3. This test determines if the brake switch signal is being received by the Electronic Brake Control Module (EBCM).
5. This test determines if an open circuit exists in the brake switch or brake lamp circuit.
7. This test determines if the malfunction is caused by the EBCM.
8. This test checks for voltage entering the brake switch.
9. This test checks for voltage exiting the brake switch.
13. This test checks for a short to ground in the brake switch circuit.
14. This test checks for a short to ground in the battery feed circuit.

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DTC C1291 OPEN BRAKE LAMP SWITCH CONTACTS DURING DECELERATION