66 Main Relay Shorted

NAME OF CODE:
66 Main Relay Shorted


SET CONDITION:
The following criteria must be met for this trouble code to be detected:

1. Ignition turned on for at least 3.4 seconds.
2. ABS main relay command not given.
3. High feedback voltage from the low side of motor.
4. Criteria 1-3 satisfied for 30 consecutive controller checks spaced 5 ms apart.


THEORY OF OPERATION:
Vehicle battery voltage is applied to the high side of the pump/motor in the hydraulic assembly by the ABS main relay whenever antilock activity may be required. The motor is run by turning on a pair of CAB output driver transistors to short the low side of the motor winding to ground. Whenever the main relay command Is not given, the feedback voltage should be low. If it is not, and the problem persists long enough to rule out noise input, the shorted main relay code is set.


POSSIBLE CAUSES:
- Anything that keeps motor feedback voltage high when the main relay is supposed to be open
- Relay contacts stuck shut
- Shorted ABS main relay driver transistor
- Shorted CAB microprocessor relay output
- Short to high voltage point in the motor feedback to the CAB microprocessor