ECU Inputs
ECU INPUTSThe air suspension system is Controlled by the ECU, which operates dependant on driver selected inputs plus those listed below. In each mode the ECU maintains the requested ride height by adjusting the volume of air in one or more of the air springs.
Battery - 12 volt supply from ignition load relay.
Engine - From A.C. generator phase tap, signals engine speed to ECU. Note that engine must be running for all height changes, except access and self-levelling when parked. The compressor will be disabled if engine speed falls below 500 rev/mm. This is to prevent the compressor drawing current from the battery when the A.C. generator is not charging.
Height sensors - Four potentiometer height sensors provide suspension height signals to the ECU.
Road speed - the vehicle speed sensor provides information enabling height changes to occur at correct road speed. Input speed signal to ECU is from a buffer unit located in the driver's side footwell.
Interior light delay unit - signals ECU if any door, not tailgate, is opened, which immediately suspends all height changes.
Parkbrake switch, manual vehicles - the parkbrake must be ON to enter ACCESS.
Gearbox inhibit switch, automatic vehicles - the transmission must be in park to enter ACCESS, parkbrake on or off.
Footbrake switch (brake light) - when footbrake is applied, and for one second after release, all height levelling is suspended below 1.6 kph (1 mph) and above 8 kph (5 mph). The purpose of this is to prevent the system reacting to suspension movement caused by weight transfer during braking and to prevent suspension wind up during height change. Note that this inhibit function is removed after sixty seconds e.g. if footbrake is held on for this time.
Delayed turn off relay - remains energized after switching engine off and exiting vehicle, enables self levelling to occur for 20 seconds. If vehicle is stationary, the ECU will energize the relay every six hours to allow self levelling to occur if necessary.
Reservoir pressure switch - when the ECU detects an output from the pressure switch indicating low pressure, the ECU will operate the compressor relay until the pressure switch indicates normal pressure.
Diagnostic plug ground - note that the two halves of the diagnostic plug are normally connected. When disconnected the system will not operate. It will remain frozen at its current height until reconnected.
Disable switch - In the disable position the switch sends a door open signal to the ECU. This freezes the system in position at speeds below 56 kph (35 mph).