Internal Main Relay

NAME OF CODE:
Main Relay Open

SET CONDITION:
The following criteria must be met for this code to be detected.
1. Ignition turned on for at least 3.s seconds.
2. ABS main relay command given.
3. None of the 4 valve (solenoid) commands given.
4. Low feedback voltage from the low side of all solenoids.
5. Criteria 1 and 4 satisfied for over 20 consecutive controller checks spaced 5 ms apart.

THEORY OF OPERATION:
Whenever the ABS main relay is closed and no driver transistor are turned on, all valve coil feedback voltages should be high. If they are not, and the problem persists long enough to rule out noise input, the open relay fail-safe is tripped. Normally a low valve coil feedback voltage during this time is interpreted as an open valve coil. However, the probability of all solenoids appearing to be open at the same time is so low that this event is interpreted as an open relay rather than as all open solenoids.

POSSIBLE CAUSES:
- Anything that keeps all solenoid feedback voltages low when they are expected to be high (no solenoids energized)
- Open relay coil or non-closeable relay contacts
- Open circuit in series with relay coil or relay contacts
- Open circuit or short to ground within CAB
- All valve driver transistors (CAB outputs) shorted
- All solenoid feedbacks to the CAB microprocessor shorted to ground



NAME OF CODE:
Main Relay Shorted

SET CONDITION:
The following criteria must be met for this code to be detected.
1. Ignition key turned on for at least 3.5 seconds.
2. ABS main relay command not given for at least 100 ms.
3. High feedback voltage from the solenoid feedback circuit.
4. Criteria 1-3 satisfied for over 50 milliseconds (ms) or 75 consecutive controller checks spaced 5 ms apart.

THEORY OF OPERATION:
Vehicle battery voltage is applied to the high side of the solenoid in the hydraulic assembly by the ABS main relay whenever antilock activity may be required. 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 (DTC) Shorted Main Relay code is set.

POSSIBLE CAUSES:
- Anything that keeps the 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 a high voltage point in the solenoid feedback circuit to the CAB microprocessor