Air Suspension Control Module: Diagnostics

The air suspension control module can store fault codes which can be retrieved using the Land Rover approved diagnostic equipment. The diagnostic information is obtained via the diagnostic socket which is located in the lower instrument panel closing panel, on the driver's side, below the steering column.

The diagnostic socket allows the exchange of information between the various control modules on the bus systems, and the Land Rover approved diagnostic equipment. This allows the fast retrieval of diagnostic information and programming of certain functions using the Land Rover approved diagnostic equipment.

Fault Detection 

The air suspension control module performs fault detection and plausibility checks. Fault detection is limited to faults that the control module can directly measure as follows:

• Sensor electrical hardware faults
• Valve electrical hardware faults
• Sensor and actuator supply faults
• Bus failures
• Control module hardware errors.

Plausibility checks are checks on signal behavior, as follows:

• Average height does not change correctly

  Height changes too slowly

• Gallery pressure

  Does not increase fast enough when reservoir filling requested

  Increases when system is inactive

  Too low when lifting is requested

  Increases too rapidly when filling reservoir

  Does not decrease when gallery is vented

  Pressure varies too much when inactive.

• Compressor temperature

  Sensor voltage too large - head and brush sensors (short circuit to battery)

  Takes too long to be readable after suitable compressor run time - head and brush sensors

  Does not increase when compressor active - head sensor only

• Sensor activity

  Signal floating

  Constant articulation when moving

When a fault is detected, the air suspension control module will attempt to maintain a comfortable ride quality and where possible will retain as much functionality as possible.

The system functionality depends on the severity of the fault.

Faults 

Faults are categorized into order of severity and effect on the system as follows (with 1. being a minor fault and 5. being a major fault):

1. Height sensor faults (hardware faults) and reservoir valve block failure

   Retain full functionality with no 'refinements', e.g. cross-link valves inoperative, no compensation for uneven surfaces.

2. Pressure sensor faults, compressor faults, corner valves stuck shut

   Road speed signal not available

   Vehicle returns to on-road mode height when next requested

   Levels at 'current' height.

3. Reservoir valve stuck open, exhaust valve stuck shut if below on-road mode height, corner valves stuck open if above on-road mode height

   Vehicle returns to on-road mode height when next requested

   Does not level at 'current' height.

4. Failure of multiple height sensors, cross-articulation when driving, calibration corrupted

   Vehicle lowers to bump stops.

5. ABS module failure, CAN bus failure

   If the air suspension control module loses communications with the ABS module or the ABS module reports a fault, the air suspension control module immediately returns to the 'default' height, which is below the on-road ride height. Once at the default height, the control module will continue to level the vehicle at this height. It is unlikely that the fault will be in the air suspension control module. When the fault is repaired, the air suspension control module will resume full functionality but the error will remain in the control module memory.

For major faults the control module will not level the vehicle at the 'current' ride height. The control module freezes height changes until it receives a manual or automatic request for height change. The control module will return to standard height if possible and freezes once standard height is achieved.

If the suspension is above the on-road height and the air suspension control module cannot lower the suspension, all height changes will be frozen. The control module will issue a message on the high speed CAN bus which is received by the instrument cluster which displays a maximum advisable speed in the message center. an immediate 'freeze' of the vehicle height is caused by the following:

• Failure of more than one height sensor - vehicle on bump stops
• Implausible articulation symptoms detected - vehicle on bump stops
• Valve or solenoid failure - corner valve stuck open below on-road mode height or exhaust valve stuck shut above on-road mode height
• Stuck corner or whole vehicle (diagnosed using plausibility of the sensor inputs).

If height change is not possible, e.g. exhaust valve failed closed at off-road height or compressor failed at access height, the control module will not level or change height.

If the air suspension control module has a hardware fault, the control module will disable all air suspension functions. Detectable hardware errors include memory error, control module failure, calibrations errors.

Fault Messages 

The air suspension has two methods which it can use to inform the driver of a fault in the air suspension system; the air suspension switch LED's and the instrument cluster message center.

When minor faults occur and the air suspension control module is able to level the vehicle to the 'current' ride height, the air suspension switch LED's will display the current ride height.

If the air suspension control module suffers a major failure and there is no air suspension control, all the control switch LED's will remain off.

If a fault occurs and the air suspension control module can determine the ride height and the vehicle is not above on-road mode height, the driver will be notified via an 'air suspension fault max speed 30 mph (50 km/h)' message, displayed in the message center.

If the control module cannot determine the height of the vehicle, or the vehicle is above on-road mode height, cannot be lowered and the vehicle speed is too high, an air suspension fault message is displayed.

If the vehicle is restricted to on-road mode height an air suspension fault normal height only message is displayed.