A085

DTC A085 "BRAKE" Warning Lamp On Due To Base Brake Failure:

Circuit Description:

The proportioning valve contains a normally open shuttle switch. This switch closes when there is a loss of pressure in the front brakes hydraulic circuit.

When shuttle switch closes, it grounds CKT AF01/AF02 and 2Y01/2Y02; turning on the "BRAKE" indicator lamp and it signals the EBCM to shut down the ABS.

The function of the diode No. 2 between CKT 2Y02 and AF01 is to prevent a grounded signal to the EBCM when either the parking brake is applied or the brake fluid level switch is closed, thus preventing a false DTC A085.

Failure Condition:

DTC A085 can be set anytime. If the EBCM detects a loss of front base brake pressure, a faulty shuttle switch, or a short in the red warning indicator lamp CKT 1L01/2Y01/2Y02, a malfunction exists.

Action Taken:

A DTC A085 is stored, ABS is disabled and the "ABS" indicator is turned "ON".

Test Description:

Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step checks for a loss of hydraulic pressure in the base braking system which caused the proportioning valve shuttle switch to close.
2. This step ensures that there is a loss of brake pressure in the base braking system and that is not related to a faulty proportioning valve shuttle switch.
3. This step isolates the condition between the ABS resistor and the Diode #2.
4. This step checks for a faulty ABS resistor.
5. This step checks for a faulty EBCM.
6. This step checks if there is a short to ground in CKT AF01 or a faulty Diode #2.

Diagnostic Aids:

An "intermittent" malfunction may be 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 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.