DTC A087: Red Brake Warning Lamp Circuit Open/Short to Battery

RED BRAKE WARNING LAMP CIRCUIT OPEN OR SHORT TO BATTERY





Circuit Description
This DTC identifies an open or short to voltage between the electronic brake control module (EBCM) and the red BRAKE warning lamp, or an open driver that prevents the EBCM from turning ON the BRAKE warning lamp. This will occur only if the system detects an ABS malfunction that may degrade base brake operation. Because the ABS is not the only device controlling the BRAKE warning lamp (the parking brake switch or the brake fluid level switch may also turn it ON), the system cannot detect a short to ground in this circuit.

Diagnosis
This test will detect an open or short to battery between the EBCM and the BRAKE warning lamp. A short to battery exists if for 2 seconds the output for the BRAKE warning lamp circuit is greater than 3.43 volts when the lamp is commanded ON. An open is detected when the BRAKE warning lamp voltage is between 3.35 volts and 5.23 volts for more than 2 seconds. This failure prevents the EBCM from illuminating the BRAKE warning lamp.

Cause(s)
- There is a short to battery in the brake warning lamp circuitry.
- The brake warning lamp bulb or fuse is blown.
- The brake warning lamp circuit is open.
- There is high resistance in the parking brake switch.
- There are poor contacts in the EBCM connector J1.
- The EBCM driving circuit is malfunctioning.

Fail Action
Only a history code is stored for this fault. If the ABS is disabled and the brake warning lamp is commanded on to indicate the possibility of base brake degradation, the ABS warning lamp will flash.

Test Description
The number(s) below refer to step(s) on the diagnostic table.
1. This step tests whether the BRAKE warning lamp circuitry is open or shorted to voltage.
2. This step checks the complete BRAKE warning lamp circuitry by attempting to turn the BRAKE warning lamp ON manually.
3. This step checks the integrity of the BRAKE warning lamp.
5. This step checks for high resistance in the BRAKE warning lamp control circuitry.
7. This tests for high resistance in the parking brake circuitry.
8. This test checks for a malfunctioning EBCM.
10. This test ensures that the malfunction is not due to a poor terminal contact at the at the brake fluid level switch.
11. This identifies if a malfunction is currently present.
12. This checks for the presence of DTC A086.
14. This test uses a scan tool to attempt to turn on the BRAKE warning lamp.
15. This tests for a short to voltage in the I/P circuitry associated with the BRAKE warning lamp.
17. This ensures that the malfunction was not due to physical damage of the circuitry.

Diagnostic Aids
An "intermittent" malfunction may be caused by a poor connection, wire insulation that has been rubbed through, or a wire that is broken inside the insulation.
Check the frequency of the malfunction by using the enhanced diagnostic feature of the scan tool as described in "Scan Tool Diagnostics." Scan Tool Diagnostics
Any circuitry that is suspected of causing the intermittent complaint should be thoroughly checked for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wiring connections, or physical damage to the wiring harness.











DTC A087 - Red Brake Warning Lamp Circuit Open or Short to Battery