2-Axle self levelling suspension problem

[Clavurion]

I know these problems have been discussed here before, but I couldn't find a similar case.

Problem is that the system first went inactive intermittent. Now it has been inactive permanently for the last month. The level stays spot on and there are no leaks, but you can't change the ride height.

With DIS it's only showing one fault code for low accumulator pressure. The accumulator showed ~8 bar. The treshold seems to be 9 bar. If the pressure drops below the system is inactivated. I activated the compressor with DIS and it started correctly and the pressure in the accumulator raised correctly. After this activation the vehicle itself activated the compressor and pressure went to correct 15 bar. The pressure was constant, no leaks. Now we started to lower and raise the vehicle. For some odd reason the compressor was not activated and the accumulator dropped below 9 bar and the system was inactive again. I also checked the compressor activating information. It was inactive. So the system was not even trying to activate the compressor even if the pressure in accumulator was dropping. When ever I activated the compressor with diagnostics it started correctly, ruling out relay fault.

So I'm stumped. All the components seem to work correctly but for some reason system is not activating the compressor correctly even if the pressure in accumulator drops. Any thoughts? Control unit fault? I've read that there has been problems with these EHC2 control units, but what kind of faults were they having?

[civdiv99]

Ok, so if I understand the gist of your post - You can trigger the compressor, but vehicle system doesn't appear to trigger it as otherwise expected.

Your fault code is just a system interpretive thing - unlike some that can give a specific out of range reading, this one is a plausibility check.

There is a pressure sensor attached to the accumulator (it's just an air tank). Low pressure supposed to trigger the compressor unless the EHC has a reason not to (for example, an over temp condition).

Sounds to me like I'd scoot under there with a multimeter and check the pressure sensor output at the low and correct pressures, and go from there. Including at the EHC module itself.

[Ricky Bobby]

what is the exact fault code you are throwing? Please paste it with full description? If you do I may be able to help you,

[killcrap]

You have a GT1, but you provide no faults. How do you expect us to help you?

Here are some troubleshooting hints for you.

Use the DIS service function, and perform ride height calibration. Clear fault memory in EHC2, and reset the flat tire monitoring system. Road test the vehicle a few meters, and let the vehicle fall asleep,(ignition off for 16 minutes)

Restart the car, and attemp to lower and raise the vehicle. If the light flashes, check the fault memory. If the fault memory shows deviation in ride height. More than likely you have a faulty EHC2 control unit. Here is how to verify.

Goto control unit functions, and select diagnosis request.
View deviation in ride height, record the readings for each corner.
View ride height sensor voltage, and record the readings also for each corner.
Now goto control unit function, and lower the front and rear together 1 time.
Goto control unit functions, and select diagnosis request again.
View the deviation in ride height, and more than likely only 3 of them have changed.
The one that has not changed will probably show 0, and must be investigated.

At this point, you either have
1) faulty ride height sensor
2) faulty EHC2 control unit.
3) incorrect installation of the sensor

Lets rule out #1 by comparing the current voltage reading of the ride level sensor to the original reading made before we lowered the vehicle. If the voltage has changed in anyway, then it is most likely fine. The EHC2 control unit can read the voltage, but cannot determine how much height deviation in millimeters. This is due to the control unit failure. The next step is to replace the EHC2 control unit, encode and perform ride height calibration. If the height deviation is readable, then the fault lies in the installation position of the ride height sensor arm.

[Clavurion]

Thanks guys so far!

As the car is not my own this comes from memory. Fault code was "Accumulator fill up requested". When the pressure drops below 9 bar the system falls inactive. Like I said in the first post I can activate the compressor with DIS and the pressure reading rises accordingly. So I don't see a problem with the accumulator, pressure sensor or compressor. For some odd reason the control unit is not activating the compressor even if the pressure is dropping. It shouldn't be overheating either as the temperature on compressor was just barely on + C (-10 C outside), threshold should be 150 C IIRC from the BMW material.

I can test the ride height sensors more thoroughly when I get the car here again, but it's hard to see a problem lying there if the control unit is not activating the compressor. Shouldn't the pressure reading be the main key point to activate the compressor? I assume DIS is showing the values as the control unit is seeing them.

[civdiv99]

Yeah, duh, clearly I blew past your mentioning that you could poll the module and see the pressure.....oops.

[Ricky Bobby]

Originally Posted by Clavurion

Thanks guys so far!

As the car is not my own this comes from memory. Fault code was "Accumulator fill up requested". When the pressure drops below 9 bar the system falls inactive.

Reconnect your car to DIS, and get the code and description for me. If you have the fault "EHC 74 Accumulator Filling Requested - Pressure Remains Constant" then your pump (compressor) is outside filling spec and must be replaced for your ride height to work and to no longer have an error on the dash.

That is what I had.