L322 Range Rover System Description and Operation
SUSPENSION
DESCRIPTION AND OPERATION
60-25
If the air suspension ECU loses information regarding vehicle speed, the ECU cannot determine if the current ride
height is suitable for the vehicle speed. The ECU immediately returns to the 'default' height, which is 20 mm below
the standard height. Once at the default height, the ECU will continue to level the vehicle at this height. A loss of the
speed signal could be due to a fault in the CAN Bus or a fault in the ABS ECU. It is unlikely to be a fault in the air
suspension ECU. It may, for example, be caused if the battery is disconnected and the steering sensor is not
recalibrated immediately after reconnection. In this case a CAN Bus fault is recorded in the error memory. If this fault
is seen, other ECU's using the CAN Bus should be also be checked for faults. When the fault is repaired, the air
suspension ECU will resume full functionality but the CAN error remains in the memory.
If the suspension is above the standard height and the air suspension ECU cannot lower the suspension or cannot
determine the vehicle height, all height changes will be frozen. The ECU will issue a message on the CAN Bus which
is received by the instrument pack which displays a maximum advisable speed in the message centre of '35MPH'. an
immediate 'freeze' of the vehicle height is caused by the following:
l
Failure of more than one height sensor
l
Implausible articulation symptoms detected
l
Valve or solenoid failure (does not include reservoir valve)
l
Stuck corner or whole vehicle (diagnosed using plausibility of the sensor inputs).
If the air suspension ECU has a hardware fault, the ECU will disable all air suspension functions. Detectable hardware
errors include memory error, ECU 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 control switch LED's and the instrument pack message centre.
When minor faults occur and the air suspension ECU is able to level the vehicle to the 'current' ride height, the control
switch LED's will display the current ride height. When the vehicle returns to the standard ride height and further height
changes are disabled, the 'HOLD' LED in the control switch will be permanently illuminated.
The air suspension ECU suffers a major failure and there is no air suspension control, all the control switch LED's will
remain unlit.
If a fault occurs and the ECU can determine the ride height and the vehicle is not above standard ride height, the driver
will be notified via a 'AIR SUSP. INACTIVE' message in the message centre. If the ECU cannot determine the height
of the vehicle, or the vehicle is above standard ride height and cannot be lowered, the 'AIR SUSP. INACTIVE'
message is accompanied with an alternating 'MAX 35MPH' message.
