mrchris

Guys few hundred miles from home, and roadside assist has a tech on the way but... 2007 gl450, got a warning for the airmatic "visit workshop" front end is slightly low. Pulled relay for airmatic and reseated and now the car will not start. Everything lights up and works, nav radio lights etc. But the last click of the key does nothing. No clicking, no turning over, nothing. Obd shows battery at 11.9v but no codes, tried jump start with no effect.

Any thoughts?

mrchris

As a follow up roadside assist tech thinks its the ecm, towing to the nearest dealer.

alx

You in park? Just a random thought.

Also check battery terminals.

Also check if you by accident knocked a relay when reseating the airmatic relay.

An ecu malfunction is not common.

Check fuses.

mrchris

Tech and I both checked and double checked fuses. He pulled up in an ml, same fuse relay panel as gl, swapped all the relays between them, his still started mine didn't. By coincidence the owner of a highly regarded independent mb shop pulled up while waiting for the tow truck. He thinks its more likely to be the front sam. Regardless he is pretty certain he can have us on the road tomorrow, dealer said we'd have to leave it for 5 days to a week and fly back down to get it. So I'll let the independent guy have at it. Funny the first thing the tow truck driver said was skip the dealer and named off two independents one of which was this guys shop. He also suggested it could be tied to theft prevention and suggested trying the other key which I am waiting for the wife to bring.

alx

Do your brake lights light up when pressing the brake pedal?

mrchris

Yes... everything else is fully functional as well.

The roadside assist tech did jump a wire on the back of the main fuse panel (in the engine bay) which triggered the starter. But with the key on and starter engaged it still wouldn't start. He was hoping to get it started and home and save towing etc.

Roadside assist guy pulled up in an ML. Same fuse/relay panel as the gl. Traded all the relays and still nothing and the relays from my gl worked fine in his ml.

I guess I'll know more in the morning.

I guess the big question is did I screw something up yanking the airmatic relay (car was off!) or did terminals touch and short somewhere. Would brief voltage somewhere on the wrong terminal for the airmatic have such dramatic damage? Was this purely coincidence? I dunno.... frustrated.

mrchris

OK as a follow up for anyone interested....

This seems to be an odd spin on the bad relay/burn out the compressor situation.

Wound up at an independent shop that was right next door based on multiple recommendations. Turns out this was a good thing. Dealer tech was talking about replacing ecm, front sam and both keys.

I had received an airmatic warning "visit workshop" and the suspension was very slowly starting to drop.

Playing with the relay killed it. As it turns out the common ground inside the primary fuse/relay box in the engine compartment was "burned out" as the tech put it. It appeared the compressor was/had failed and had a bad ground and the wrong relay was in the airmatic relay spot. It was similar but not quite right. They think this caused the load to ground out through the relay box damaging the common ground on the circuit board inside. They were able to solder it and get it back up and running. They also replaced the airmatic compressor as well.

Took them a good half day but I was on the road again early afternoon and it came in under a grand for all of it.

We talked extensively about it as I was concerned the relay manipulation I did might have caused it. He said no the damage was clearly long term and slow and eventually soon would have failed. Playing with the relays finished it off but that's it.

Oddly enough I'd been concerned with the compressor pump as it hadn't tripped a warning before but was starting to get really slow to do anything and all four corners would drop slightly every once in a while. He was pretty adamant that even shorting out the relay terminals would have popped a fuse before doing any significant damage (not that I want to put it to the test) but pulling relays in and out flexed the board inside enough to break the already damaged ground.

I got lucky in that this happened next door to one of the highest rated independent shops in Oregon and they specialize in MB. Had this happened 500 miles down the road in the middle of nowhere, it would have been a massive tow bill at a minimum.

So frustrating and messed up the trip some, but ultimately not terrible. Back on the road in roughly 24 hours and with a reasonable repair bill.

sak335

Thanks for posting a follow-up. I'm curious how much you were messing with the relays to cause such a problem because it seems like a strange result if you were just pulling it and reseating it.

I've pulled relays a ton of times on other cars and never seen a hint of a problem.

mrchris

Well, I think the issue was the air compressor was grounding back through the relay box and it eroded the ground on the circuit board inside the box. When you dismantle the relay/fuse box there is a plastic case that the relays plug into on top and on the bottom various cable connectors but inside the case in between is a circuit board with traces between certain pins.

That board was damaged/weakened where the common ground was and was likely near failure anyways. The little bit of flexing going on pulling it and reseating it was enough to break the connection.

I agree normally it should be a non-issue and the shop that worked on it was surprised but at the same time it was pretty clear the damage was long term.

I had something kind of similar happen many years ago on a Jeep Grand Cherokee. Wouldn't start one day, took it in and the starter was burned out. Replaced it and it was fine but three days later it was out again. Figured out that of the several ground straps between the body and engine, one was missing another was disconnected at one end and the remaining two were so overloaded that one of them more or less melted and was reduced to a few threads of wire. The bad ground overheated/overworked the starter causing it to fail and then causing the replacement to fail.

Once the ground was fixed the next starter lasted for many years.

But when something is like that circuit board inside a case like that where you can't see it, it's really easy to miss that damage unless you take it apart. Whether it was the compressor, the wrong relay or something else who knows. Yeah yanking relays might have been the final straw but because it was already nearly gone.