Dealer Can't Diagnose 1998 E320 Check Engine Light - Mercedes-Benz Forum

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post #1 of 8 (permalink) Old 03-02-2010, 08:12 AM Thread Starter
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Dealer Can't Diagnose 1998 E320 Check Engine Light

Today marks my 7th visit to the dealer.

My car won't throw a code, but the light continually comes on.

The car will fault when driven at moderately cool temperatures (30-50 degrees) for about 20-40 minutes at a consistently high speed. So if I leave my house when the engine is 'cold' and drive for about 20-40 minutes, I will come to a complete stop. The engine will idle down and come to rest. When it comes to rest, the engine will shudder and the light will come on. Sometimes it shudders once and nothing happens, then it will shudder a few seconds later and the light will come on.

The car runs fine, with the light on or off.

The car, since I've had it for 5 years, will drop about 50 rpms for a split second and then will pop back up to normal idle. The car only will shudder before the light comes on.

When they tried replacing the relay, but that didn't work. The car didn't drop the 50 rpms, but would still shudder and engage the light.

They replaced a cable that involved 'cold start' and said with 99% certainty that it was the culprit, but it wasn't.

The car doesn't fail every time I drive in those circumstances, but will come on within two weeks of them resetting the light. All when I come to a complete stop after a period of warmup driving.

They've told me I can bring in my car when the light has just come on for an instant diagnostic, but I have yet to have that sync up with their shop hours and my schedule.

Anyone have any insight on to what this could be?
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post #2 of 8 (permalink) Old 03-02-2010, 08:18 AM
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Has the car really been diagnosed at a dealer with Star? In some cases codes do not pop up but if the check engine light comes on, I cannot see how one could avoid stored or present codes.
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post #3 of 8 (permalink) Old 03-02-2010, 08:30 AM Thread Starter
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Yes, they have it. But they're saying it's not registering a code. Or presenting a code that could be hundreds of things...
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post #4 of 8 (permalink) Old 03-02-2010, 08:51 AM
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Codes will be stored for some time even when the problem is no longer present. Maybe you drove the car for too long after CEL come on?
Why don't you buy a scanner and scan for the code after the light shows?
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post #5 of 8 (permalink) Old 03-02-2010, 08:56 AM Thread Starter
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I've brought in my car within 12 hours of the light coming on and it seems to make no difference.

I'd also asked about my own scanner or taking it to any mechanic that Im near, but unless it's a Mercedes scanner it won't give enough accurate info.

The crux of this is, the scanner / codes aren't going to reveal anything at this point. From the symptoms I've mentioned, has anyone had any similar problems that also didn't register codes?
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post #6 of 8 (permalink) Old 03-02-2010, 09:49 AM
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The first thing I would do is ask them for the code and post it here. You are correct that the inexpensive hand held scanners will not read all the MB codes but it should read enough of them for the gurus here to provide some possible causes and solutions.

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post #7 of 8 (permalink) Old 03-02-2010, 12:15 PM
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If it happens 20 to 40 minutes after starting it should not be cold any longer. Does it reach around 190 degF within 5 minutes from start and stays there?
When did you service your cooling system (coolant/thermostat) last? Problems with the sensors lately? Do you flood it when you say you go fast?

It seems as if your problem were simple and related to upkeep.

A car would show appreciation for preventive maintenance by never leaving his owner stranded.

Defensive Driving is never having to say you're sorry: a true love story between man and machine.
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post #8 of 8 (permalink) Old 03-02-2010, 03:53 PM
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I am not sure if this will help or not but I have the same M112 engine in my ML320 as you do in your mercedes. For a time I was also getting a CEL and my scanner would read "error" when I tried to check it. Advance Auto and Autozone scanners would do the same thing. This all happened after I changed the catalytic converter. I finally got a reading-misfire codes stored in memory and P0221. I changed the Mass Air Flow Sensor and have not had a problem in the last 10K miles.
I have no idea if this is the problem being that the similarity between your problem and mine was the undefined CEL and erratic idle. It might be worth your time to at least clean your MAF with CRC Mass Airflow Sensor cleaner. It would not hurt and at most cost you about $5 or so.
Hope you get it figured out soon.

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