Google is not really helping but since someone here may know....
Have 2008 Expy EL with rear air suspension. Has always worked great but over the cold months started to get a sag on one side and the air compressor making more and more noise. Figure I'd wait it out until warmer. Few days ago came out and saw rear was in low rider status on both sides (different from the usual "lean"). Started it up and air compressor didnt come on. Poop, the compressor finally bit it.
I know there are coilover replacements but I have no time to swap them out (long hours and riding on the bump stops is not fun). Rockauto had them & fedexed overnight for an extra $13 (BTW, had I known they were 30 miles away I would not have overnighted them, thanks buds). Put in the compressor and nothing. Check 60A fuse, its OK. Check 10A logic fuse, its OK. Pull relay and bench test - its OK.
Break out the DMM. I see 7.3V on the coil side of the relay. OK, whatever - I'll jump the load side of the relay and see what happens. Back in business, compressor starts and back end comes up. I put my DMM on the coil side of the relay and decide to pump it up until I see the 7.3V drop out. It doesnt, it just stays at 7.3V. Weird. Back end is in sky jacker state but its better than the bump stops.
There is a VDM module that takes the signal from the rear suspension ride height & sends the output to the relay / compressor. There are also some solenoids and vent commands (as well as CAN bus stuff), but its weird that its sending a low volt signal to the relay. I found exactly one thread on the internet from 2013 with the same issue - and of course there are no replies or updates (thanks bud).
I will swap out the air bags and rear shocks (its got 189K miles), but the VDM may need some dealer programming according to the internet? I really dont want to start ordering parts willy nilly. I'll check the ride height indicator when its not so wet out, that might be sending an bad signal.
Anyway, thoughts & ideas appreciated.
On the '96 Expedition there was a switch under the dash (or in glove box) that had to be triggered if you were jacking up the vehicle, etc. If you didn't do it in the proper order you might have to go through a gyration to reset the system. I sold the vehicle 10 years ago but remember that switch.
At least make sure if yours has it, you have it set correctly.
Reading your post, I'm pretty sure you already know all that.
Look for corrosion etc. on the height indicator.
Thanks, the newer ones are on the cluster (to shut off the air). Its just weird that it was working, compressor died, and now it's not.
Hmm, unless old compressor is still working and this was something different. Once it stops raining I'll go underneath it.
Check your height position sensors.
I think you have a less complex version of the Ford sourced system in my LR3. The ride height sensors and the valve block are the only trouble spots beyond the compressor which ou have changed. When one corner is giving trouble my system will dump all the air so the car will ride level on the bump stops back to the shop. I would expect you could use a good scanner to figure out which corner the problem is.
Update for the Google's sake.
Inspected vdm and ride height sensors / wiring, no issues. Picked up a code reader that would read the chassis codes, found a c1810 (or c1830) for height position sensor out of range.
Aha, my sensor(s) could be bad! I researched the code (and actually found the 100 page tech manual from ford) and discovered that my fault was due to a voltage _difference_ between the sensor readings. I had a leaky right rear air bag and kept jumpering the pump to get it to work daily - as a result the RR was usually low and the LR was in sky jacker land. I tried to figure out the vent circuit to drop everything down but couldn't find an easy way - so I just jumpered the pump back on and cranked the rear up until they were equal. Rake. Reset the codes and it appears all is well. Rear leveled out and no codes all the way home.
I think the 8V I saw on the relay coil circuit was a low voltage current test to see if the coil side was open / shorted - one of the faults I got was a "relay coil failure" when I had the relay unplugged.
Anyway, it looked like I needed to level the suspension and reset the codes for the system to work after a compressor change.
