4.8 Air Suspension issues, EHC 74 code and compressor won't switch on

[LVR]

Hi

ISTA is the newer version of INPA (as I understand it). I use it to remove errors and reset EHCII module which is what controls the system. It allows diagnosis and test programmes etc.

I highly recommend it.

From those pics the first thing that stands out is that you have the same issue I did, which is a plausibility error on your front left sensor. If you look at the voltages on all of your other sensors, you'll see that they are within a similar range, except for that one.

If you use INPA, look at the Offset Values from the ECU screen. In my case the offset value was -5145 whilst the other wheels were all around 400 - 450.

The sensors when operating correctly put out a voltage depending on where the arm is (ie ride height). When you are setting the ride height you are telling the system which voltage you want and it goes to that point.

It has a limited range and the sensors are also prone to being knocked out of place or water ingress messing them up.


This is how I found my sensor


You can see the arm pointing down.

It should be like this



If it is in the right location I would be starting by replacing the sensor. They're pretty cheap and easy to install.

Then reset the ride heights etc.

If that doesn't work then I used a combo of INPA and ISTA to re-write the error in the sensor range to get it back.