Test 3B

Test 3B: Repairing -- System Relay Circuit:

System Relay Circuit Schematic:

Hydraulic Control Unit:

SYSTEM RELAY CIRCUIT

When Its Monitored
It's monitored during the start-up cycle.

Set Condition
The system relay is used to provide 12 volt power to the Controller Antilock Brake (CAB) solenoid drivers and the Pump/Motor relay coil. The system relay is normally energized by the controller (pin 57) and is tested for proper function during the start-up cycle to see that it is not providing 12 volt output when not energized.

Possible Causes:
^ ABS system relay control wire shorted to B+
^ ABS system relay output circuit shorted to B+
^ Stuck system relay contacts
^ Failed CAB
^ Open ground circuit to the relay box