Travis R

After ignoring a "Display Error" on the cluster for a few days the car finally let me know it meant business by dropping the RF corner onto the bump stops.
So while waiting 4 hours for a flatbed I had plenty of time to look through all the modules to try and sort out what actually went wrong.
9107: Fault in CAN communication with control module Full air suspension or ABC active body control
So it turns out, the display error was that it wasn't telling me the car was too low.
So naturally I assume the control module for the Airmatic has died. I found a good used replacement, many years younger than mine. But I still have the same error after replacing it. And the car remains on the bump stops.
The same error code is immediately rewritten after clearing and restarting the car. And the Airmatic pump never turns on to inflate the bag.
So I need some help.
Here are the possibilities as I understand them
1. The replacement part is NOT good. (this seems unlikely as there are very few posts about this part failing)
2. The fault is in the wiring.
3. ????

I looked at the pins on my original control unit as well as the replacement, and everything looks to be in order. No bent pins, no missing pins, no corrosion of any kind.
It's a little more difficult to inspect the plugs, but nothing looks too suspicious upon inspection.
Can someone tell me WHICH wires are responsible for the CAN communication? I'm happy to ohm them out, if I can find the other end of the harness.
There are about a million wires going to this module, so I'd really prefer to not have to check them ALL.
Thanks in advance!

kevm14

Step 1: Check for power(s) and ground(s) at the module, ideally when plugged in. Can be easier said than done. Usually requires back-probing or a piercing probe. Or, check harness pins when unplugged using a test light or ideally something that actually draws a couple amps to verify wire integrity. Open circuit voltage doesn't always mean everything is good.

sexyxe

Digging this up, as I am having the same issue and rather than making a new thread I'd see of OP had any resolution. All my fault finding is saying the computer isn't telling the pump to power on, but every individual piece is functional.

sexyxe

I'll add for trouble shooting I've checked relay and it's fine, as is the fuse. The pump works when given 12V. The relay is not receiving power when the car is turned on. The interior fuse F37 is still in tact and is also not receiving power. The ride height sensors are functioning correctly.

I'm waiting to get a scan tool to see what codes it's giving me. But the issue I have, appears no power is being sent to the pump/no demand signal for power. Which would make me think the airmatic control module. Is there a way to test that in the car?

sexyxe

Had these codes upon plugging the computer in. Of note the cars had all the bags replaced and hasn't been reset since. I cleared them, then these 3 came back. Pump did not run.


This

And this on start

These came back after start but pump didnt run.

sexyxe

This morning got the pump to run by bypassing the relay. 12v is getting to the relay on the power side, but no signal power is being received.

On to trying the computer and seeing if that's getting power or what. It's odd it is sending codes though but not song anything else

sexyxe

With better trouble shooting I can get 12v to pin 85 on the relay but pin 86 has 4.3v so the relay isn't tripping. When the relay is plugged in both 85 and 86 have 12.

It seems that pin 86 on the relay should be the ground but it has a bit of voltage.

It reads the same at the airmatic control module.

I hate electrical issues.

sexyxe

Resolved. No kidding, ended up being another relay. After so much trouble shooting my mechanic recommended over the phone to go back to basics. Buy another genuine relay and start from there.

So that's what I did. $65 new airmatic relay, reset the computer and its back to running fine.

I used three separate, known good relays in the slot during my trouble shooting but the Merc 5 pin is specially listed as 'airmatic relay' so maybe some special juice is inside it. New one measures 70ohms, old 67. Both make contact under 12v, but the new one seems to be working in the car properly.

Here's to hoping I get a few more miles out of it.