73 Watchdog

NAME OF CODE:
73 Watchdog


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

1. High voltage feedback from the low side of motor in middle of ABS warning bulb check.
2. Criterion 1 satisfied for 10 consecutive checks spaced 5 ms apart.
3. Low voltage feedback from low side of motor afier completion of ABS warning bulb check.


THEORY OF OPERATION:
The CAB includes a watchdog circuit external to the microprocessor, internal to the CAB, to guarantee a return to conventional braking if the microprocessor stops functioning.

During normal CAB operation the watchdog circuit sends a signal to the base of the warning lamp relay enable driver transistor to open the normally closed ABS warning lamp relay, thus keeping the lamp off. If the watchdog circuit fails, two things happen:

- It disables the ABS main relay so that the CAB can't turn it on.
- It also allows the CAB to ground the ABS warning lamp relay control circuit allowing the relay to close and light the ABS warning lamp.


POSSIBLE CAUSES:
- Malfunction of the CAB's external watchdog IC