Test 25A - System Relay Ground Circuit

Test 25A: Repairing -- System Ground Circuit:

System Relay Circuits Schematics:

Hydraulic Control Unit:

NOTE: You must perform Test 3A, before proceeding with this test.

SYSTEM RELAY GROUND CIRCUIT OPEN

When Its Monitored
The test is conducted at power-up. The system relay output voltage is tested once each 5ms for a total period of 495ms.

Set Condition
The system relay supplies the Controller Antilock Brake (CAB) solenoid drivers with B(+) power when it is commanded on by the CAB. It is turned off by the CAB to shut off Antilock Brake System (ABS) functions in the event of a trouble code or a loss of B(+) to the system. The relay supplies a ground to the ABS warning lamp to illuminate the lamp when the relay is turned off. The trouble code is set if the system relay output voltage is less than 5 volts when the relay should be on or more than 5 volts when the relay should be off during the power up test.

Possible Causes:
^ 0pen system relay normally closed contacts
^ 0pen relay box ground circuit
^ Stuck system relay normally open contact
^ Loose or corroded connector terminals
^ Failed relay box
^ System relay control circuit shorted to B(+)
^ System relay output circuit shorted to B(+)