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Discussion Starter #1
Hey All,

Kinda just stopped by to say hi. Haven't been by in a while. But thought I'd share a story in case it may help anyone down the road.

Several months ago we started having an occasional issue. You'd get in, turn the key, and nothing would happen. Come back a few hours later and everything would be fine. Weird.

So I tested the battery and sure enough, it had a bad cell. Cool. Problem solved!

Or not. A few weeks later, got a call from my wife. Car won't start. She got a jump from AAA and all was well. I looked at it and the terminal was corroded. Shoot. That one's on me. I cleaned it up, put some anti-corrosion gook on it and put it back on - tight this time. Cool. Problem solved!

Or not. A few weeks later, my wife took the car to the dentist. Wouldn't start when she came out. Had it towed to a good Mercedes mechanic. They said they couldn't get the key to turn and it needed a new ignition tumbler. It did. I always had trouble getting it to turn. My wife could do it every time, but I had issues. A few hundred bucks later, that was done. Cool. Problem solved!

Or not. Yesterday I drove it to work. Came out after a long day and, you guessed it, wouldn't start. Towed it over to the mechanic again. They're pretty sure they have it this time. They said it had several trouble faults and there was a technical bulletin indicating that it was a bad ESP controller. He's confidant this will fix it.

By the way, he's a very good mechanic. We talked after the last trip and agreed that they likely hadn't found the problem, but they couldn't get it to recur. They went through several diagnostic steps and eliminated some possibilities but we needed the car back. This time it did do it for them and they tracked it down pretty quickly. It's not a cheap fix, but should take care of it.

Anyone else heard of this problem? He said it was something that Mercedes knew about but didn't issue a recall for. But they did have enough information available to diagnosis it with a high degree of confidence. We'll see I guess.

So, problem solved?
 

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Discussion Starter #4
Well...

The car is still at the mechanic.

They got the ESP module, but did more testing and decided that wasn't the problem. They're sending that part back. I'm *very* glad I didn't spend $1,500 for a repair only to find out in a few days/weeks that it didn't fix the problem.

But after messing with the car quite a bit, they tell me they were able to make the problem happen reliably. So what is it? You'll be shocked.

K40 Relay. Damn-it. I wish I had done a little more research. I know I've read about this problem before, but when looking today, I found several references here to a no crank issue exactly like we have. You try to start the car, but nothing happens, then you hear the cooling fans come on. Weird.

The mechanic feels sure they have found the problem, and it's less expensive than the ESP module, so while I'm dumping some money, it's less than I was prepared to spend. And I do feel good about the mechanic. They have some hours tied up in this and did admit that their first diagnosis was wrong. He suspects this is why the car was sold, and to tell the truth, I'm thinking he's right.

If that's the case, it kind of stinks that people would do that. I understand, but not good. I'm really hoping this puts an end to this issue. But if not, or if I didn't have a mechanic that could track this down, I'm not sure what we would have done. Worst case, we would have sold the car and disclosed the issue. I'm sure we would have lost several thousand dollars. So spending a few hundred bucks to get it diagnosed and fixed is money I'm happy to spend. I'll admit, though, it will take a few months for the car to earn my trust. I'm very encouraged that they say they can reliably recreate the issue, though, and I'd say I'm reasonably hopeful that this will be the end of it.

I’ll post a couple more updates down the road. Wish us luck!

(edit) Hum. After reading a bit more, I'm a little worried - I never got a check engine light. We'll see.
 

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Discussion Starter #5
Just got the car back. He said they could get the no-start to happen by jiggling the wiring harness at the K40 relay, then shake it again and it would start, so he's pretty confidant, but told me to call right away if there is any more problem. They really put a lot of hours into this.

When he mentioned the jiggling the wires, I wondered if it was the cold solder issue I read about in the sticky. I asked him to save the part. Just popped it open at my desk and there is no sign of a soldering issue, so if this proves to be the fix for our problem, it seems to be for another reason.

I'll make a post in the k40 thread when I'm confidant this is resolved. Worth noting, the k40 on our 2003 SLK230 is a different part number than the one noted there. A 170 545 02 05. Date code on the part is 30.10.02.
 

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Discussion Starter #6
Sorry I haven' been by in a while. The good news is, there's been very little to talk about. I'm confidant at this point that the issue was resolved with a new K40 relay. Looks like I posted that about 9 months ago, so confidence is high. The car has been rock solid ever since and we really enjoy it.
 

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Thanks for following up. The K40 relay is probably the single most common point of failure on the R170.
 
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