Diagnostic and Fault Recovery

DIAGNOSTICS AND FAULT RECOVERY

The ECU incorporates Fault Recovery Strategies to minimize the effect of a system failure. A serial data link is provided to allow diagnostic information to be retrieved using the Lucas hand held tester. This is also used to set height sensor datum when required. Note that the serial link connector is colored black for identification purposes. Any faults stored in the ECU memory, from the previous or current running period will cause the ECU to flash the RAISE and LOWER lamps for 30 seconds. followed by continuous illumination. If the ECU registers a system fault, it will store the fault in the memory. The fault recovery programme will operate the system depending on the nature of the fault as follows:

Speed sensor fault - The ECU will place the system in standard height and activate inhibit.

Height sensor fault - The ECU will place the system in standard height and activate inhibit. Note that if more than one height sensor fails, the ECU will deflate the air springs to the bump stops.

WARNING: If any two failure occur the system deflates and lowers vehicle to its bump stops, it is possible to drive the vehicle provided that great caution is exercised. The vehicle ride will be extremely uncomfortable and only low speeds will be possible. It is essential that the vehicle fault is rectified as soon as possible.

Pressure switch fault - The ECU will register pressure switch failure if it detects that the compressor has worked for a programmed time with normal air spring operation possible. The ECU will periodically operate the compressor as air is required. The vehicle will be inhibited to standard.

Compressor fault - The ECU will register compressor failure if it detects that the compressor has worked for a programmed time with normal air spring operation not possible. The ECU will attempt to place the system in standard ride height, or a safe lowered position (which could be system deflated). The system will be inhibited from further ride height changes.

Air leaks - During normal operation the ECU correlates the operating time of the compressor with air usage. If compressor use is greater than programmed, the ECU will register an air leak and attempt to place the system in standard ride height, or a safe lowered position (which could be system deflated). The system will be inhibited from further ride height changes.

Valve block fault - The control of each air spring is monitored to determine that every valve is working correctly.
1. If the ECU detects an air valve stuck open it will attempt to adjust the vehicle to standard height or a safe lowered position (which could be system deflated). The system will be inhibited from further ride height changes.
2. If an air valve is stuck closed above standard height the ECU will deflate the other three air springs.
3. If an air valve is stuck closed, at or below standard height, the ECU will attempt to adjust the other springs to the same height and activate inhibit