1992 400E CEL won't turn off

[mr.lovrak]

My new to me 400E (03/92 production, California model) has a really bizarre intermittent check engine light that will stay illuminated indefinitely unless I disconnect the battery. It has drained the battery completely once already. Sometimes there is no check engine light, and everything seems fine. The other times the light turns on and gives a 17 flash code from the led behind the passenger strut. The code appears to be, "Data exchange fault between individual control module" if my research is correct. When I try to pull the code when the light is off I don't even get a 1 flash code, it doesn't flash back after a 3 second push. I was also unsuccessful at trying to manually clear the code. On occasion the light turns on AFTER I shut the engine off, and it will stay illuminated for about 7 seconds.

Because people will ask, the upper harness and eta harness are updated units.

This is probably something that has happened to other people, I have absolutely no idea where to start with this one. Any help is appreciated.

 

[gsxr]

If the CEL remains on with the key off/removed, the DM is defective... you can disconnect it for now, but may need to replace it to pass emissions testing.

 

[mr.lovrak]

The funny thing is I just passed Oregon emissions yesterday haha

I’ve been a Mercedes owner for 2 weeks now and I’m trying to catch on to this lingo. I have predominantly owned aircooled VW’s, vintage M cars and redblock Volvos of all things, but I have eyed V8 Sacco-Era MB’s for a while. I assume that DM means ‘diagnostic module’ and not ‘dungeon master’. Is the DM shared with other vehicles? For instance should I keep my eye out for California market M119 cars from later ‘92-95?

 

[nocfn]

All of the cars were to CA spec IIRC. The lower harness should be inspected as well. Not a bad idea to disconnect battery, remove each of the control modules in the CAN box and re-seat them. There is plethora of knowledge here, it will require a lot of reading. Search the HOW TO area and you will find most of what you need.

 

[gsxr]

The funny thing is I just passed Oregon emissions yesterday haha

I’ve been a Mercedes owner for 2 weeks now and I’m trying to catch on to this lingo.... I assume that DM means ‘diagnostic module’ and not ‘dungeon master’. Is the DM shared with other vehicles? For instance should I keep my eye out for California market M119 cars from later ‘92-95?

LOL! Yes, DM = Diagnostic Module, located under the passenger footwell carpet, behind the metal panel. Twist the round knob to release the module. Search eBay for the same part number as the one currently installed. They are really cheap, as they rarely fail.

The ONLY purpose of the DM is to monitor the other computers and look for emissions-related issues, and when it sees any, it turns on the CEL in the cluster. It's only used in North America and the car will run & drive fine without it, if you don't mind not having the watchdog running around the yard.

Oh, and welcome to Mercedes ownership! I'd recommend visiting the De-Coding sub-forum to read the stickies on how to check codes, and buy either a blink code reader or SDS digital scanner for advanced diagnostics. Most everything you need to know to maintain & repair your 400E will be on this forum. If posting about engine diagnostics, remember to mention if your car has optional ASR or not.

 

[mr.lovrak]

Quick update: I pulled the DM, it appears to not be the original unit. With a yellow paint marker it has written on it, “94 m-benz 400E” which is funny because a 94 would be an E420 but I digress. The MB part number is 015 545 13 32 - 07, Bosch number is 0 216 200 916. It seems like the 0155451332 had an -01 and -07 variant, with Bosch numbers being -920 and -916 respectively. The -920 seems to be for M106 cars, the -916 looks like it’s shared with M120 and some M119 cars. I bought one on eBay just now for $17 shipped, I’ll update this thread when I install it.

 

[gsxr]

015-545-13-32 is the correct part number, what I was expecting you to find. And yes, many people get the year/model mixed up... I've seen "E400" more than once as well.

The EPC only shows the one part number, without variations... should apply to all W124+M119, and select R129+M120, only with LH-SFI fuel injection (through USA model year 1995). No 6-cyl cars though. Fingers crossed that the replacement solves your problem!

 

[mr.lovrak]

I installed the replacement DM, same part number, and same problem. Check engine light either doesn’t come on with the key in position 2, or remains on when the key is out. Also the battery quickly went flat the other day while the DM was removed after just maybe 36 hours of not using the car. It happened randomly, I’ve left the car locked for a day or so a few times since the DM has been removed so the battery draw is most likely related to whatever the heck is happening with the diagnostics part of the car.

 

[gsxr]

I installed the replacement DM, same part number, and same problem. Check engine light either doesn’t come on with the key in position 2, or remains on when the key is out.

Drat! So much for the easy fix.

Also the battery quickly went flat the other day while the DM was removed after just maybe 36 hours of not using the car. ... so the battery draw is most likely related to whatever the heck is happening with the diagnostics part of the car.

There may be something screwy going on at the 38-pin connector. I'd look at that next. This can cause intermittent power drains. Link below with details:

HOW-TO: Replacing the 38-pin Diagnostic Socket (X11/4) | "HOW-TO" Tutorial Articles

When I recently purchased my 500E it had a crippling Battery Drain which would totally drain it overnight. Removing all of the Fuses & Relays did not eliminate the parasitic drain. I did discover that the LH module was causing the current draw as it was not shutting down when it should be. As...

www.500eboard.co

 

[mr.lovrak]

Thank you gsxr for the helpful links and info. I tried reseating all of the modules and tracing wires to see if there was anything obvious going on, no luck there. I removed the modules and unbolted the 38 pin connector and there wasn't any red flags, but looking down into the pins from the top did show that at least one had turned a cakey white. I wrote down the pins on a diagram and carefully tore into the connector. The slide that releases the pins came mostly out before breaking off inside. After removing the pins it's obvious that they were "corroded" on the surface but nothing too obvious about pins grounding or shorting on each other. I installed shrink tube on all of the exposed pins and wrapped them together neatly and put them back where the connector would be until I get a replacement. I've cycled the car on and off twice now and the check engine light behaved like it should, coming on with the key in position 2 and then turning off when the engine starts and then shut off, which is not what it was doing. I will be monitoring it over the next few days, checking the battery often, but I'm hopeful that the 38 pin connector was the culprit.

 

[gsxr]

That is great news! The corrosion becomes conductive, so even though no wires touch physically, the corrosion causes significant problems. On the bright side, the new connector may fix your problem permanently. Make sure when you put it back together, the pins all "click" fully into place, otherwise the sliding piece won't close. And remember to have the sliding piece only ~1mm out when inserting the pins.

 

[nocfn]

Dave - Would it be a decent idea to periodically remove the negative cable, and spray some Deox - IT in the connector to clean possible corrosion seen or unseen? As part of the clean out the sunroof and cowl drains, twist torpedo fuse annual MX?

 

[gsxr]

Dave - Would it be a decent idea to periodically remove the negative cable, and spray some Deox - IT in the connector to clean possible corrosion seen or unseen? As part of the clean out the sunroof and cowl drains, twist torpedo fuse annual MX?

This is inside the 38-pin diagnostic port, which is generally sealed & dry. I'm not sure if there would be any useful preventive maintenance, especially since it's a relatively rare failure... only a handful of people have reported issues.

However, it would be a good idea to give it a visual inspection periodically, maybe once per year or so. Shine a flashlight into the socket. A shiny new one looks very, very different than an old corroded one. I'd expect it to be a once-per-lifetime of the car replacement.

 

[nocfn]

This is a good response as new folks come to read and learn.

 

[mr.lovrak]

I figured I would give a ~1 week update and give some closing to this weird problem Incase anyone else come across this with their car.

I’ve been using the car as my primary car the last week since I’ve disassembled the 38-pin diagnostic port, and I have not been able to replicate the issue. I was not having fuel pumps that stayed running unlike other people had, my only symptoms were a cel that came on after removing the key and staying on until I removed the negative battery strap, and seemingly random power draws that would leave the battery dead overnight. If I parked the car and the cel light stayed on I’d disconnect the battery so I do not think that the power draw was simply because a dash light was lit. I would also frequently be unable to pull codes from the led, even thought the physical light was illuminated. That’s the gist of it.

Thanks to all of you, especially gsxr, for helping me get this 400E back on the road.

 

[Jimbo]

Thanks for the update. Been following...

Just a side note, and not sure if related. Does your car have a CD changer in the trunk? Something was wrong with mine (in the 500E) where it works and all but would draw the battery down when the car was off. Disconnected it and no more draw down of the battery.