L322 Range Rover System Description and Operation
SUSPENSION
60-24
DESCRIPTION AND OPERATION
Diagnostics
The air suspension ECM can store fault codes which can be retrieved using TestBook/T4. The diagnostics information
is obtained via the diagnostic socket which is located in the fascia, in the drivers stowage tray. The socket is secured
in the fascia panel and protected by a hinged cover.
The diagnostic socket allows the exchange of information between the various ECU's on the bus systems and
TestBook/T4 or a diagnostic tool. This allows the fast retrieval of diagnostic information and programming of certain
functions using TestBook/T4 or a suitable diagnostic tool.
Fault Detection
The air suspension ECU performs fault detection and plausibility checks. Fault detection is limited to faults that the
ECU can directly measure, as follows:
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Sensor hardware faults
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Valve hardware faults
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Sensor and actuator supply faults
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Bus failures
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ECU hardware errors.
Plausibility checks are checks on signal behaviour, as follows:
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Average height does not change correctly
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Height changes too slowly
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Suspension moves in the wrong direction.
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Reservoir pressure
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Does not increase when reservoir filling requested
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Does not decrease when reservoir used to lift vehicle
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Does not decrease when reservoir is vented
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Pressure varies too much when inactive.
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Compressor temperature
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Increases when compressor inactive
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Does not increase when compressor active.
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'Energy' used to change height of corner
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Too much 'energy' used – height change takes too long or long term filtered height does not reach target.
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Sensor activity
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Signal floating
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Inconsistent signal characteristics – signal on one side of axle is varying but other side remains static
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Constant articulation when moving.
When a fault is detected, the ECU will attempt to maintain a comfortable ride quality with restricted functionality of the
air suspension system.
The system functionality depends on the severity of the fault. The faults are defined as minor or major faults.
Minor faults are:
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Most sensor faults (hardware faults and plausibility faults)
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Cross link valve failure
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Reservoir valve failure.
For most minor faults, height changes are inhibited except for a return to standard height. If the suspension is not in
standard height, the ECU will respond to a request for manual or automatic height change to return the vehicle to
standard height. The ECU will continue to level the vehicle at the 'current' ride height.
Major faults are:
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Compressor faults
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Plausibility errors – for example:
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Average height does not increase when lifting and the vehicle is moving. This could be caused by a
compressor fault or a fault in the reservoir valve.
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Reservoir pressure decreases when filling requested. This could be caused by a leak in the common gallery
in the valve block or connecting pipe.
For major faults the ECU will not level the vehicle at the 'current' ride height. The ECU freezes height changes until it
receives a manual or automatic request for height change. The ECU will return to standard height and freezes once
standard height is achieved.