different air suspension pain 4.8is

[dhyrk3]

TwinsPoppa, thanks for this literature!

as I understood, the compressor shouldn't start if the engine is 'off'. And the only possible control to do is to lower the vehicle as long as the ignition is 'on'.

However, what I'm experiencing is, at least every other day, both front sags. As soon as I unlock the door, the air bags inflates to the normal height again.

any thoughts?

Originally Posted by TwinsPoppa

Control Modes (See attached for flow chart)

Sleep mode
If the vehicle is parked, it enters Sleep mode after 16 minutes. No further control operations are executed. A "watch dog" wakes up the control unit for a few minutes every 6 hours (wakeup mode) in order to compensate for possible inclination of the vehicle. (Vehicle height may only be corrected once as air supply unit only operates with engine running.)

Wake-up
In wake-up mode, the control unit is woken up for a set period of time in order to compensate for possible inclination of the vehicle. Inclination of the vehicle can be caused by large temperature differences or by minor leaks. Adjustments to the front and rear axles ensure that the vehicle is visually level. To minimize power consumption, the vehicle is lowered
only. The nominal level of the lowest wheel serves as the nominal level for all other wheels. The lowest nominal level to which the vehicle is lowered is the Access level (-35 mm).

Exception:

if the vehicle is parked at Access level, the vehicle is lowered to max. -50 mm in wake-up mode. If the vehicle is parked for a prolonged period of time and there is a leak in the system, further loss of pressure does not produce a change of ride level since the weight of the body is born by the auxiliary suspension and the residual tire pressure.

Advance /Overrun

When the vehicle is woken out of sleep mode by the load-cutout signal (VA), it normally enters advance / overrun mode. Since the engine is not (no longer) running in this mode, however, there are restrictions on the control operations that can be performed in order to conserve the battery. Ride level compensation is restricted to tolerance ranges of 20 mm and 25 mm in the up and down directions respectively. This serves to reduce the frequency of control operations. All control operations in advance / overrun mode are executed as long as pressure is available in the accumulator. When the accumulator is empty and the engine is turned off, control operations are directly driven by the compressor. User-activated changes of ride level and filling of the accumulator are not possible.

So, after 15 mins, X goes into Sleep mode. After 6 hours its supposed to go into Wakeup mode and compensate as long as there's enough pressure in the Pressure Accumulator. Have you observed what it looks like overnight (after 6 hours)?

If your X tries to correct the ride height after 6 hours, but does NOT, then maybe there's not enough pressure in the Accumulator because either its faulty or the compressor in the Air Supply unit is bad (could not pump enough pressure into the accumulator before going into Sleep mode). I assume that the EHC2 module (Control Unit) is working properly as this is what gives the commands and the rest of the system executes them.

This still does not point to where the problem is exactly. This is also assuming there's absolutley no leak (which is still my best guess). I know, lots of assumptions.

Okay, so someone correct my thinking or feel free to comment.