Antilock Braking System (ABS)

Fig. 346 Code 18: Electronic Brake Control Relay Coil Circuit Shorted To Battery Or Coil Shorted:

Electronic Brake Control Relay Coil Circuit Shorted To Battery Or Coil Shorted:

Circuit Description:
Ignition voltage is supplied through terminal "85" of the electronic brake control relay. The EBCM is then able to energize the pull-in coil by completing the ground circuit at terminal "22" of the EBCM. The magnetic field created closes the electronic brake control relay contacts and allows battery voltage and current to be supplied to the EMB's and EBCM, which supplies voltage to the motors and solenoids.

DTC Will Set When:
DTC 18 can be set after the EBCM commands the electronic brake control relay "ON." This test monitors the availability of current/voltage to the motors, solenoids and EMB's. A malfunction of this type will not allow voltage to be available to the motors, solenoids and EMB's; therefore, ABS operation would not be allowed if required. DTC 86 is set with DTC 18 if the rear channel is not expected to be in the home position.

Action Taken:
A malfunction DTC is stored, ABS is disabled and the "ABS" warning lamp is turned "ON."

DTC Chart Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Indicates if the EBCM is capable of controlling the electronic brake control relay as commanded.
2. With the electronic brake control relay removed, voltage should not be available at terminal "86". Any voltage at this point would indicate that the electronic brake control relay circuit is shorted to a voltage source.
3. Checks for a short across the electronic brake control relay coil.
4. Checks for an internal short in the electronic brake control relay between the BATTERY feed terminal "30" and the relay pull-in coil.
5. Ensures short to BATTERY was not due to physical damage of the electronic brake control relay control circuit.
6. Identifies whether the malfunction is due to a shorted connection in the Dash to Engine connector.

Diagnostic Aids:
An "intermittent" malfunction is most likely caused by a poor connection, rubbed through wire insulation, 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 Tech 1.

Any circuitry, that is suspected as 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.