DTC A018: ABS Enable Relay Coil Circuit Shorted to Battery

ABS RELAY COIL CIRCUIT SHORTED TO BATTERY





Circuit Description
Ignition voltage is supplied through terminal 85 of the ABS enable relay socket. The electronic brake control module (EBCM) then is able to energize the pull-in coil by completing the ground circuit at pin Al 1 of the EBCM. The magnetic field created closes the ABS enable relay contacts and supplies battery voltage and current to the EBCM, which supplies power to the motors.

Diagnosis
This test checks for a short to battery in the relay coil circuit. Such a short would cause the relay to remain off all the time. The relay coil is considered shorted to battery when the coil circuit voltage at the controller is greater than 3.4 volts.

Cause(s)
- The relay coil circuit is shorted to battery.
- The enable relay coil has low/no resistance.
- The EBCM driver circuit is malfunctioning.

Fail Action
This is a critical operational fault. The ABS is disabled and the ABS warning lamp is turned on. The brake warning lamp is turned on only if the rear piston is not at the top of the bore. This could cause degradation of the base brakes.

Test Description
The number(s) below refer to step(s) on the diagnostic table.
1. This step indicates if the EBCM is capable of controlling the ABS enable relay as commanded.
2. With the ABS enable relay removed, voltage should not be available at terminal 86 of the relay socket. Any voltage at this point would indicate that circuit PNK was shorted to a voltage source.
3. This step checks for a shorted coil.
4. This ensures that a malfunction was not due to a poor connection.

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.
The frequency of the malfunction can be checked by using the enhanced diagnostic function 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 A018 - ABS Relay Coil Circuit Shorted to Battery