Description & Operation (page 12 of 26)

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

l

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

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

l

Pressure sensor faults, compressor faults, corner valves stuck shut 

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Road speed signal not available  

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Vehicle returns to on-road mode height when next requested  

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Levels at 'current' height.  

l

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

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Vehicle returns to on-road mode height when next requested  

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Does not level at 'current' height.  

l

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

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Vehicle lowers to bump stops.  

l

ABS module failure, CAN bus failure 

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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:  
 

l

Failure of more than one height sensor - vehicle on bump stops  

l

Implausible articulation symptoms detected - vehicle on bump stops  

l

Valve or solenoid failure - corner valve stuck open below on-road mode height or exhaust valve stuck shut above 
on-road mode height  

l

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 a 'air suspension fault max speed 18.6 mph (30 km/h)' message 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.