Ok so I’ve run out of ideas on this after trying about everything that would logically make sense to me. So I’m relying on the group’s intelligence to help me think through this.

For context, I replaced the front right upper control arm a couple of weeks ago. Had to swing the ride height sensor out of the way during it. Worried I damaged it. Off road screen shows normal wheel height so I don’t think this did anything

I also went through and wire wheeled the undercarriage and then sprayed everything with rust protection coating. Right after that the fault started and happens at every start.

Symptoms: Start vehicle, no issue. Compressor kicks on. No issue. After a minute or so I get a yellow suspension fault indicator and a message that it’s now in normal height only. Also, special programs off. No other issues. Drives fine. Doesn’t drop.

Codes:
U0421
C1131
C1A20
U0132
Have a bunch of stored C1A3* codes as well

Where I’m at:
I started with the filter/air supply. I disconnected the inlet and exhaust hoses on the back of the compressor. Still faulted.

I then disconnected the outlet hose from the dryer canister to the valve block. Tons of air blasting out. I was actually pretty caught off guard by the volume of air this compressor produces! But, seems the compressor is strong. I also reconnected the intake hose and it slightly reduced the volume of air pumped out.

I then tested the reservoir valve block pressure sensor. I don’t know what an acceptable range is but the 5V reference voltage there tested at 4.95V. With the valve block connected and the reservoir pressurized it read about 31 ohms (actually don’t remember if it was kilo-ohms or something else). I then started releasing the pressure from the reservoir by loosening the hose to the reservoir. The resistance went down into the 25 ohm range. After removing the sensor it tested at 15 ohms. I hit it against the table top a few times which made some of the old desiccant powder come out.

I then removed and cleaned out the valve itself. Wasn’t dirty inside or anything. Nothing that made me think I fixed anything.

I just reinstalled everything and same fault.

I’ve gone through and sprayed everything around the compressor, valve, reservoir with soapy water. Basically zero bubbles.

While the compressor is running I can’t hear any leaks. With the volume of air coming OUT of the compressor the leak would have to be serious. There’s zero sign of leak anywhere.

Other thought:
It took a good 2-3 minutes to fault when I reinstalled the valve and the reservoir was empty. If I then turn off the vehicle and start again, it’ll fault in about 10-15 seconds. It SEEMS like it faults when it hits a specific pressure level. So if I’ve tried raising the vehicle and drained the reservoir, it takes longer to fault. Just an observation.

Other possibilities:
-Bad pressure sensor?
-Totally missing a huge leak somewhere?
-Bad wiring to the EAS control module?
-Valve is stuck and cleaning didn’t help?
-I hit something or sprayed something when coating the undercarriage?

I don’t know where to go at this point. I hate buying parts without knowing for sure what the issue is. Thanks in advance!

 

My bet is on the height sensor, either need a new one or recalibrated. Check the wires as well to the height sensor. Everything seemed to happen after you moved the height sensor.

 

Yeah I should probably double check that sensor. However I had a week or two with no issues after the control arm repair.