Hey all!

I have a 2009 Sl550 with 77K miles. The car has been great and has been dealer serviced on time its whole life. 2 days ago it started misfiring. I had it towed to the shop and STAR stated a bad mass airflow sensor. I had it replaced and all was well until the problem started again yesterday. Star has given the following codes.

0641 cylinder 4
0653 cylinder 3
0634 cylinder 1
0908 g3/4 implausible signal right O2 sensor
0629 misfire
0565 right O2 sensor voltage too high
0228 throttle valve actuator frozen (I'm in Texas)
0600 O2 sensors incorrectly connected
0569 g3/3 left o2 sensor voltage too high
0439 Electronic analysis system for the oxygen sensor in the ECM is faulty


The shop says that the frozen actuator code leads them to think the ECU needs to be replaced, to the tune of a $2636 part (part number 273-153-55-79).

Has anyone experienced anything similar? Should I just bite the bullet and get a brand new ECU or try another route/get a reman?

 

Are you sure some animal didn’t chew through a wire harness somewhere?

 

Thanks for the response. I haven’t tested or for that, it seems unlikely since it’s garaged and I live in the downtown of my city, but it could definitely be possible.

Another detail that might help. When I turn the car off and on again the check engine light stays on but it won’t misfire until about 10 minutes or driving. Misfire is also most noticeable at low speed and idle.

 

Have you checked for oil in the ECU? There is a known problem with oil travelling along the wiring harness into the ECU.

 

thats the first I’ve heard of that being a problem. I haven’t gotten into the ECU yet, I’ve been hoping there for a more minor repair cost to be the solve.

What causes the travel across that harness? If that’s the case what would need to be addressed to stop that in the future?

 

I am not sure if this is your problem, you might ask at the shop you are using? May not apply to your engine?

https://mbworld.org/forums/sl-class-...blows-ecu.html

 

That's wild, I've never heard of something like that happening. I'll bring that up to them. I'd like this repair to be something less costly than the ECU but after going through more threads it's seeming more likely to be the issue.

 

Check your wiring harness thoroughly for any breaks, cracks, melts or for any "oil wicking" at any of the connections. If you're confident your harness is good, I would continue troubleshooting. I'm getting a lot of those same errors, but my wiring harness was poorly repaired (a bad solder joint) so I'm almost positive my wiring harness is causing a cascade of errors. I have it's replacement, but just need find time to install it. Also confirm that both of your batteries are maintaining the proper charge. If the ECU does not see the amount of voltage it needs, strange things can start happening so be sure to check both.

When I got those those errors, I though my ECU was bad as well. So I purchased a numbers matching (serial and part), used ECU on eBay and sent it in with my original one (along with a spare key and the ignition switch) and had it cloned. I installed the replacement unit when it came in, but the errors persisted. In my eyes, that confirms that the issue lies elsewhere. But just to be sure, (and before I sent them anything) I asked the shop, "if my original ECU has faults, won't those faults cross over to the cloned ECU"? He said that errors and codes reside in a part of the ECU's brain that don't get cloned or copied. Of course, I have no idea if that is accurate so all I have to go is their word. But the total cost for the process came in at around $600 with shipping there and back. Remember, you'll have to send your ignition switch and a key with the ECU so there were no immobilization or communication issues or conflicts. Getting the ignition switch out can be a bit tricky and kind of a pain. But if a novice mechanic like myself can do it, that's proof that it can be done. So if you think you still want (or need) to replace your ECU, you might want to investigate this option. I used High Tech Mobile out of Encinitas Ca, and I think they did a pretty good job.

But I hope all of this helps in some way. I've been chasing my gremlins for well over a year now, but I've narrowed it down to either an exhaust leak or a bad wiring harness. But if it turns out to be neither of these, I'll have to drop back and punt. AGAIN!!!

GOOD LUCK!!

 

Hey all,

I checked out the wiring harness and connectors, no oil or cracks thankfully. The batteries have good voltage as well. I sent the ECU to Pressertech in Georgia. I just got the call that it had in fact gone bad and needed to replaced. They programmed a new one and said it'll be shipped back to me today. Fingers crossed this fixes the car, I'll update the thread once I get it back.

 

Hi, I was reading your post and was about to suggest pressertech. I was about to pull the trigger on a ecu from them after months of tinkering with my c300 with many fault codes. Turns out it was my o2 sensors. Started out with 02 sensor codes followed by ecu codes and transmission codes and misfire codes and so on and so on. They seem legit and respond quickly to questions! Let us know how you made out! Good luck!

 

I got my ECU back from them and the car runs smoother and better than ever! I got it back on September 5th and gave it time to see how it went, all was great until this morning. On the way to work the car started misfiring and intermittently cutting the power steering, I have no idea what could be causing that and I would hope that they're unrelated faults. I'm not quick to think that this is the fault of the ECU since it ran fine for the last few weeks. I guess it's back to the indy shop for now.

Has anyone else experienced this or have an idea of where to go from here?

 

Hey, Thanks for the update! Sorry to hear you still have issues! I am sure at minimum disappointing and frustrating. I am still a newbie at all of this and maybe a bit overly optimistic about the longevity of the brand but i hoped for more from Mercedes. Not sure where your ecu is on your car but mine is located on top of the hot engine. Looks cool but really? Hope the shop you take it to can figure it out. If you havent already done so check out "Pine Hollow Auto Diagnostics" on youtube. The guys name is Ivan and he gets deep into the electrical systems on all types of cars. Also "Diagnose Dan" is another. Maybe they have worked on your model and have seen some issues. Worth a watch! Thanks

 

Where you able to fix it ? I am facing the same issue !

 

Does anyone know how he solved this problem? I tried to contact him but he is not replying .

 

I would suggest starting a new thread so that we know exactly what car/engine you have and the exact symptoms and codes you are dealing with. Even small differences between you and the OP of this thread can lead to totally different solutions.

 

Will do , Thank you