Friday night I pull into the garage at midnight. I hear the air injector pump start running and treat it as a normal sound. I turn off the engine and the pump keeps running. At first I think it will stop in a few moments. It doesn't. I restart the car, and then stop it, thinking that the software or some relay needs a reset sequence to turn off the pump. Doesn't work. In hindsight I should have just pulled fuses, but I had been at work for many hours and my brain wasn't processing as well as it should. The pump motor failed, it burnt itself out. I spoke with a tech via roadside assistance and they informed me that I should have the car towed to a dealer. They said that the air bladders could empty while driving and the car could lower near enough to the tires so that damage could result. The next day was Saturday and it was hard to get hold of any service department. Finally found one and they also strongly suggested a tow. So, I called a towing service recommended by the dealer. They turned out to be very experienced with Mercedes and had encountered this kind of situation before. The driver told me that getting a car that has lost its air onto the flatbed was a little delicate. He said he had situations where the car could move forward or backwards at very slow speeds, but any bumps of turns would scrape the body against the wheels. He said that getting the car towed on Saturday instead of Monday was a good call as the car could settle and make getting it on the tow truck much harder.

Car is now at the dealer, we'll see what happens.

I am stunned by all this. I find that a design that could make a vehicle unsafe to drive (or tow without damage) due to an air pump failure (or software controlling the air pump) seems just a little on the delicate, not very well thought out side.

Anyone else have experience with anything like this? I want to make sure this NEVER happens in the future. I also want to understand if there are any more "gotchas" like this one of which I'm unaware.

This is a 2003 SL55. I’ve had lots of creak and rattle issues (all resolved) but never a mechanical failure, till now.

Comments?

 

sl55 has an abc hydraulic system, no air pump. could be a bad valve if the suspension has sagged. i think you were told wrong by the dealer.

 

Well, I defnitely got bad advice from the Roadside Assistance tech and the other dealer I called. As noted above the SL55 has a hydraulic system. The dealer doing the service told me that many years ago there was an "S" with a air suspension and many myths and legends have spread thoughout Mercedes techdom from that car. I got sucked in to an urban legend.

However, they are still not sure what motor or pump was running with ignition off for over 40 minutes. In the right front of the car, near the SBC box, what pump or fan comes off and on every few minutes? What could keep running with a sound like a small shop vac for so long? No error codes are posted in the diagnostic memory.

 

Wasn't it the SBC box itself? It 'moans' whenever I get into the car and press the brake before starting it. Is that the sound you're describing?

BTW, when you say the motor 'burnt out' you don't mean something like this right? https://mbworld.org/forums/sl55-amg-sl63-amg-sl65-amg-r230/123578-sl55-spontaneous-combustion.html

 

No, no fire. Just the sound an overheated motor makes when the bearings seize.

The sound isn't a groan. Can't tell exactly where it is coming from. The sound is very similar to a vacumn cleaner. It comes from around the SBC box area, but I can't tell exactly where. When it failed, when it kept running, it was actually louder than a vacumn cleaner, sounded like a large shop vac.

 

End of the tale.

The problem was an air injector pump used for emissions. A relay became stuck (no error code) and the motor burnt itself out. All fixed now.

Still can't believe the nonsense I got from Benz support on the phone.

Live and learn.

 

There is a service bulletin out for that issue. Just ask me next time and I'll give you the right answer the first time.