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Discussion Starter #1 (Edited)
TL;DR Occasionally if the car is standing still or moving very slowly (like in/out of a parking spot) the engine will shut off. This most often happens a few seconds after the car is started. The second variant is if the car is moving down the road, the engine will shut off and after about one second restart on its own and everything carries on as if nothing happened. You effectively just lose power for a moment. Obviously, the latter is a lot scarier, but it also happens a lot less often.

Full details: 2006 C230

  • No fault codes, no warnings on the dash.
  • No rough idling, or engine noise.
  • When the car is still and the engine shuts off, it always cranks and starts fine after. However you need to turn the key all the way counter-clockwise first, otherwise turning it clockwise to 'crank' does nothing.
  • When the car is still and the engine shuts off, all the dash lights come on, like they do when you first insert the key.
  • When the engine 'restart' happens while moving, all the electronics go out (I'm fairly sure, it only happened twice) and the dash lights all flash for a moment before the engine restarts on its own and continues as if nothing happened.
  • Tested and both issues happen with two different keys
  • Tried to wiggle both keys in the ignition, it never triggers the issue.
  • I've checked and cleaned the battery terminals.
  • Monitoring the voltages through the dashboard secret menu, the UB is USUALLY at 14.2V while driving, however often while turning or coming to a stop it goes down to 13-13.5V and a few times I saw it rapidly plunge to 12.9V and right back up to 13.5V.
  • Using a testing tool, the battery tests as 'needs to be replaced' since it's old. But again, the car never has issues starting, even twice back to back.
  • The cranking voltage tests as low (assuming due to the battery). The charging tests just fine. I can post the detailed results from the tool if you think they're relevant.
  • These issues started in the summer.
- Earlier in the summer I was dealing with an occasional no crank no start issue where you'd get in the car, turn the key and while everything lights up, there was no cranking. You had to turn it all the way counter-clockwise (or even take it out I don't remember), put it in again and the car always started fine. No exceptions. That issue basically transitioned into this issue and now I haven't had that happen in a while. At the time I checked all the relevant fuses and everything checked out (which makes sense given that 95% of the time the car starts and runs 100% normally).

That's everything I have. This is a real pain in the ass because it doesn't happen often enough to be a real problem, but losing power while driving is scary, especially with a baby on the way. Any help is appreciated.
 

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You might want to check your ground (neg.) lines/cables coming off the battery.. Just don't look at the bolts holding the cables to the engine block and chassis.. Unbolt them.. Clean cable connectors and the contact points on the car..
 

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Discussion Starter #3
You might want to check your ground (neg.) lines/cables coming off the battery.. Just don't look at the bolts holding the cables to the engine block and chassis.. Unbolt them.. Clean cable connectors and the contact points on the car..
Crap I forgot to mention that I checked and cleaned the battery terminals. They were clean and the issues continued.
 

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No fault codes, no warnings on the dash.
I assume you are using a generic OBDII scanner, This will likely require SDS/Xentry to properly diagnose.

However you need to turn the key all the way counter-clockwise first, otherwise turning it clockwise to 'crank' does nothing.
That is normal behavior for when the engine shuts off unexpectedly.

When the car is still and the engine shuts off, all the dash lights come on, like they do when you first insert the key.

When the engine 'restart' happens while moving, all the electronics go out (I'm fairly sure, it only happened twice) and the dash lights all flash for a moment before the engine restarts on its own and continues as if nothing happened.
This sounds like a bad EIS (ignition switch).

Tried to wiggle both keys in the ignition, it never triggers the issue.
The key communicates via infrared signals, so unless the EIS or keys were physically damaged to the point of being loose, this will have no effect.

Monitoring the voltages through the dashboard secret menu, the UB is USUALLY at 14.2V while driving, however often while turning or coming to a stop it goes down to 13-13.5V and a few times I saw it rapidly plunge to 12.9V and right back up to 13.5V.
Voltage fluctuations are normal. If you get drops just turning the steering wheel, you may have an issue with the power steering pump or an idler or tensioner pulley causing the serpentine belt to bind. But I doubt this is related to your problem.

If this is an EIS problem, you will likely only find some odd CAN buss communications errors using SDS. A common fault when the EIS is that various CAN bus systems switch to "single-wire mode".
 

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Ya, Rodney nails it as usual , listen to what Rodney has to say, he is an ace when it comes to MBs.. The only thing I have a concern about is that plunge to 12.9v and back to 13.5v.. The 13.5v is normal..12.9v is not.. Find out why the plunge is happen, you might have found your problem..
 

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Discussion Starter #8
Ya, Rodney nails it as usual , listen to what Rodney has to say, he is an ace when it comes to MBs.. The only thing I have a concern about is that plunge to 12.9v and back to 13.5v.. The 13.5v is normal..12.9v is not.. Find out why the plunge is happen, you might have found your problem..
It happens I think only while slowing down to a stop, as the transmission is shifting down through all the gears. Could it be a bad voltage regulator/alternator? I can't think what else could be leading to that happening. If I understand correctly the UB value displayed there is the 'system' voltage, not the battery voltage, so the alternator either isn't keeping up or the regulator is bad.
 

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UB is the system voltage. With the engine running, it should be right around 14v at idle. I'd say anything between 12.7v and 14.2v at idle is fine. Under acceleration, the sparks plugs demand more power, so you may see some drops, but coasting to a stop, you should see around 14v. Turning the wheel will cause the PS pump to drag on the engine which might give a slight drop, but it should not be enough to cause electrical gremlins.

My SL550 has a bad EIS. What it does is just randomly, maybe once a week, drops communication with various CAN bus components. If it drops them all, then it's literally like quickly switching it off and back on. If I am moving at speeds over 5mph or so, the engine does not shut off, but everything else "blips". All the "idiot" lights on the dash illuminate briefly and I get various, random error messages on the MFD, like "SRS -Visit Workshop", "Repalce Key", or "BAS/ESP Inoperative". If I am stopped, more moving very slowly, the engine will shut down. Also, sometimes when it does this, it only affects one item, so I may only get a brief blip of an SRS light, or slight tug on the seatbelts as the tensioner resets.
 

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Discussion Starter #10
Interesting, it sounds quite a lot like what I'm experiencing, except for the part where it often happens to me soon after starting the car/while moving slowly. What do we do to fix it?
 

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If it is a bad EIS, the solution is to replace it. The challenge is in properly diagnosing the problem so that you are certain it is a bad EIS. The interesting thing is that even using SDS, there may be no errors or events stored for the EIS itself. Instead, there may be some random CAN bus faults in other systems. What I have found using SDS is that going into "System Diagnosis" under the "Body" group will give errors like "CAN Communication of control unit xyz is in single-wire mode".
 

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Discussion Starter #12
How do I replace the EIS? It seems tricky to even find the part number. I feel like if you haven't fixed this issue on your car I don't have much of a chance...
 

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Unless you have SDS with Developer Mode enabled, you will need to have the dealer do it. SDS with Developer has an option to save the EIS coding, then transfer it to the new switch. There used to be an option where you could order the EIS along with a "green key" or "orange key". This special colored key comes from the factory and is programmed with the 24 possible key codes for your VIN. MBZ stopped selling these over the counter a year or two ago, so now only the dealer can use them. My advice, if you don't have SDS and know how to do this is to find a shop (dealer as a last resort) that does.
 

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Discussion Starter #14
Okay. There is a shop in town that specializes in this. I'm assuming they'll have an SDS to scan my car with. You're saying the telltale sign that the EIS is bad is if there are messages on the CAN bus of various systems going into 'single-wire mode' ?

By the way, I was reading over one of your previous messages. This often happens when we're trying to accelerate and/or when moving slowly or idling. If the cause wasn't a bad EIS but rather a bad alternator/voltage regulator (since it's impossible for the weak battery to be causing this, right?) then are there specific codes that I can look for in the SDS to verify?
 

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I really doubt that it's a voltage issue unless you have a bad ground wire that is intermittently disconnecting. I've "limped home" with a bad alternator and voltage dropping to around 10v with no issues like that.
 

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Discussion Starter #16
Okay so I contacted that shop near me telling them the issues I'm having and asking if they have a scanner with which they can check if there are issues with my EIS. This is the answer I got back:

"I talk to my tech he told me he can not work on unknown eis issue.
There is no guarantee if clone eis with same model will resolve all issue you have. He advise me to have you look in ELV lock system on c class."

I wrote back saying:
"So is there something you guys can do to see what is wrong with my car or do I have to find out myself? "

This is pretty frustrating. I guess I'll need to start calling shops and asking if they have an SDS scanner...
 

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The ELV/ESL (steering wheel lock) would not be an issue here as it only engages when you first insert the key - it's the buzzing/gear noise you hear that unlocks the steering column.

Yes, do find someone (a shop or even a fellow forum member) with SDS. Get them to do a full scan as well as that "System Diagnosis" scan under the "Body" section. Post your location - maybe a nearby forum member can help.
 

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Discussion Starter #18
I have one small update.
I had the car scanned with a better scanner, but still not an SDS. It found this stored message.

Now, in the past my brother accidentally yanked apart these cables connecting under the driver's seat (a yellow connector). The car complained about airbags, but since then I've taped the connector together and there have been no issues or messages since. Could this code be related to that accident or could it be connected to/the source of my main problem of the topic?
 

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Problems with SRS won't cause any issues with engine operation. That fault is just pending, and could be caused by the car stalling (i.e. low voltage or voltage cut-off during the stall).
 

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Discussion Starter #20
Alright, that's what I figured. Tomorrow I'll hopefully have the car scanned with a proper SDS and we'll get some real information.
 
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