C1285

EBCM/Brake Indicator Control Schematic:

CIRCUIT DESCRIPTION
The proportioning valve contains a shuttle switch that is normally open. This switch monitors front brake hydraulic pressure. This switch closes if there is a loss of pressure in the front brakes. When shuttle switch closes, it causes to ground CKT AF01. This action turns ON the red BRAKE warning lamp. It also alerts the Electronic Brake Control Module (EBCM) of the base brake failure. The EBCM then disables the ABS system. The function of diode # 2 between CKT 2Y02 and AF01 is to prevent a false base brake failure signal to the EBCM when either the parking brake is applied or the brake fluid level switch is closed.

CONDITIONS FOR SETTING THE DTC
This Diagnostic Trouble Code (DTC) will set when the following conditions are met:
^ This DTC can be set anytime after initialization.
^ The shuttle switch closes due to a loss of front brake hydraulic pressure.
^ Short to ground in the CKT AF01.

ACTION TAKEN WHEN THE DTC SETS
A malfunction DTC is stored, ABS is disabled and the ABS indicator lamp is turned ON. If the malfunction occurs during an ABS event, the rear channel will apply longer to return home under the increased rear brake hydraulic pressure.

CONDITIONS FOR CLEARING THE DTC
^ Conditions for the malfunction are no longer present and the Tech 2 scan tool Clear DTC Information function is used.
^ One hundred drive cycles have passed with no malfunctions detected.

DIAGNOSTIC AIDS
The frequency of the malfunction can be checked by using the Enhanced Diagnostic function of the Tech 2 scan tool, as described in Enhanced Diagnostics.

An Intermittent Malfunction - may be caused by a rubbed through wire insulation. Any circuitry that is suspected of causing the intermittent complaint should be thoroughly checked for improper mating.

DTC C1285 Red BRAKE Warning Indicator ON Due To Base Brake Failure (Part 1 Of 2):

DTC C1285 Red BRAKE Warning Indicator ON Due To Base Brake Failure (Part 2 Of 2):

TEST DESCRIPTION
The numbers below refer to step numbers on the diagnostic table.
[2] Checks the shuttle switch for open switch position.
[3] Checks the shuttle switch for closed switch position when applying brake pedal to confirm base brake failure.
[4] Checks the condition of the red BRAKE warning lamp control circuit.
[5] Checks for an open ABS resistor.
[6] Ensures that the malfunction was not due to a faulty EBCM.
[7] Checks for either a short to ground in CKT AF01 or a malfunctioning diode # 2.