1993 300E 2.8 upper wiring harness, ETA wiring insulator, and OVP relay - Mercedes-Benz Forum
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#1 (permalink) Old 11-07-2010, 09:44 AM
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Lightbulb 1993 300E 2.8 upper wiring harness, ETA wiring insulator, and OVP relay

Dear all, first thanks for reading my first post. Really appreciate your help.

My mother's 1993 Mercedes 300E 2.8 recently has a "check engine light" problem. The car still runs fairly well, although couple of weeks ago she experienced engine stall when the car is going slight uphill, and when the car is started in cold weather, sometimes the engine would "stutter" (or the RPM of the engine will go like roller coaster). The car still have fairly low mileage (about 55K I think). We helped her to do some basic diagnostic (using the radio shack "home build" code scanner), and found that only Pin #6 (some minor SRS issues) and Pin #3 (Mass Air Sensor??) reported code errors. However, we were not able to reset the error codes with the code scanner (to see if they are really "hard" error codes), so we disconnected the battery for about one hour and reconnect it. The "check engine light" is still ON.

Questions:
  1. Is it long enough to clear all the memory and remaining electrical power for just disconnect the battery for one hour? Or should we disconnect it and wait for longer? How many hours then?
  2. I read a lot of posts in this forum, and seems a lot of people mentioned the culprits are probably (a) upper wiring harness, (b) ETA wiring insulator, and (c) OVP relay. Is there any step-by-step way to REALLY make sure any of these parts REALLY need to be replaced? Could we do the trouble-shooting by ourselves, or this is really a job for the professionals?
  3. Someone mentioned to check the OVP relay to see if it's 000-540-52-45, and if it is, then change it to the new part 000-540-67-45. HOW could I locate the OVP relay in this car and see the part number? Do I have to dissemble anything to reveal the OVP relay part#?
  4. Also what does the "ETA wiring insulator" looks like and how do I know whether it need to be replaced or not??
  5. How do I check the "tag" at the harness (what year) or splice the insulator and see if it's original? Could someone please post some pictures here in the forum??

Many many thanks!
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#2 (permalink) Old 11-07-2010, 11:14 AM
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Quote:
Originally Posted by ohman View Post
[LIST=1][*]Is it long enough to clear all the memory and remaining electrical power for just disconnect the battery for one hour? Or should we disconnect it and wait for longer? How many hours then?[*]I read a lot of posts in this forum, and seems a lot of people mentioned the culprits are probably (a) upper wiring harness, (b) ETA wiring insulator, and (c) OVP relay. Is there any step-by-step way to REALLY make sure any of these parts REALLY need to be replaced? Could we do the trouble-shooting by ourselves, or this is really a job for the professionals?[*]Someone mentioned to check the OVP relay to see if it's 000-540-52-45, and if it is, then change it to the new part 000-540-67-45. HOW could I locate the OVP relay in this car and see the part number? Do I have to dissemble anything to reveal the OVP relay part#?[*]Also what does the "ETA wiring insulator" looks like and how do I know whether it need to be replaced or not??[*]How do I check the "tag" at the harness (what year) or splice the insulator and see if it's original?
What specific codes are you getting, by pin? You shouldn't have to disconnect the battery to clear them. They need to be cleared within a few seconds of the reading, then ignition off after each clear.

The wiring harness is tested by inspection - do you see any crumbling insulation at the end points on the top front of the engine? On the ETA it's insulation, not insulator, in other words the same issue as the upper harness - the insulation crumbles and causes shorts. I'd focus first on reading and clearing the codes, and the upper harness inspection. The OVP is behind the battery, fairly easy to get to. Those two part numbers should both be good - the EPC shows them as interchangeable.

Last edited by deanyel; 11-07-2010 at 02:46 PM.
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#3 (permalink) Old 11-07-2010, 01:48 PM
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I just replaced my MAF in my 93 2.8 as well. It did cause a engine check light and occasional stall during idle and acceleration. I bought a new Bosch MAF online ($200) and the CEL disappear immediately and car runs fine ever since.

98 Toyota Sienna (boring but keeps running)
95 Jaguar XJS
79 450 SLC
93 300E 2.8 (totaled by Silverado)
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#4 (permalink) Old 11-08-2010, 07:39 PM
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Hi bigwiki, thanks so much for the info! By the way, where did you get your MAF online ($200)? Also, did you try to use "CRC MAF cleaner" to clean MAF first and see what happens? I wonder whether I could just "clean" the MAF (or really need to replace the MAF) to get the problem resolved? Thanks much!

Last edited by ohman; 11-08-2010 at 08:01 PM.
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#5 (permalink) Old 11-08-2010, 08:17 PM
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Originally Posted by deanyel View Post
What specific codes are you getting, by pin? You shouldn't have to disconnect the battery to clear them. They need to be cleared within a few seconds of the reading, then ignition off after each clear.

The wiring harness is tested by inspection - do you see any crumbling insulation at the end points on the top front of the engine? On the ETA it's insulation, not insulator, in other words the same issue as the upper harness - the insulation crumbles and causes shorts. I'd focus first on reading and clearing the codes, and the upper harness inspection. The OVP is behind the battery, fairly easy to get to. Those two part numbers should both be good - the EPC shows them as interchangeable.
Hi deanyel, the codes that I was getting was NOT consistent. Here are the detailed list:


Pin #3 (continuous fuel injection): code 10 (only showed once, the 2nd time I tried to read it, the code was gone without me even tried to reset it)

Pin #6 (SRS): code 8, 9
  • Code 8: voltage supply interrupted
  • Code 9: SRS Warning Lamp (with flashing SRS warning lamp Impulse counter scan tool button held too little time to read out the DTC memory or too long or erase DTC codes. Reread codes).
Pin #7 (air conditioning): code 1 (should be "no fault found" right?)


As for the wiring harness, I do not see any serious "crumbling" insulation at the end points on the top front of the engine. They just look a bit rusty and old at the end points (I will try to post some photos later). The car has always been garaged, and never met any snow - living in sunny cupertino california area for the past 17 years. I agree with you that I also want to focus first on reading and clearing the codes, but I can't seem to be able to read the codes consistently with the same results every time, and I can't seem to be able to "clear" the codes (even by disconnecting the battery for more than 1 hour). Thoughts or comments on this?

I will try to see if I could locate the OVP (behind the battery) by myself. When you said the EPC shows them as interchangeable, what do you mean by EPC (sorry about this stupid question)? Also why would people recommend the new part 000-540-67-45 in other threads? Is there a special reason for this? Thanks again!

Last edited by ohman; 11-08-2010 at 08:24 PM.
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#6 (permalink) Old 11-09-2010, 06:45 AM
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Photos of the harness would be good. Also check the label near the source plug for a production date. Eratic codes can be a sign of a bad harness.

For engine operating problems concern yourself only with pins 3, 8 and 14. Forgot about the others for now (although voltage supply interrupted has an OVP sound to it).

The EPC is electronic parts catalog from Mercedes, the factory's view of what part goes where, very authoritative but can be wrong. When a part number is outdated they show it as such, or if not as interchangeable as in this case. AutohausAZ.com is selling 52 45 for your car. Possible that they are both wrong but the chances are pretty slim.
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#7 (permalink) Old 11-09-2010, 11:13 AM
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Quote:
Originally Posted by deanyel View Post
Photos of the harness would be good. Also check the label near the source plug for a production date. Eratic codes can be a sign of a bad harness.

For engine operating problems concern yourself only with pins 3, 8 and 14. Forgot about the others for now (although voltage supply interrupted has an OVP sound to it).

The EPC is electronic parts catalog from Mercedes, the factory's view of what part goes where, very authoritative but can be wrong. When a part number is outdated they show it as such, or if not as interchangeable as in this case. AutohausAZ.com is selling 52 45 for your car. Possible that they are both wrong but the chances are pretty slim.
Hi deanvel, thanks so much for your help! Here is a photo of the harness:



Uploaded with ImageShack.us



Uploaded with ImageShack.us

I also noticed that the number on the harness is 124 440 3908 KS 02 06 92. So I guess the first 10 digits (124 440 3908) are the part number, and the 02 06 92 is the manufacturing date? Am I correct on this? Is the 02 06 92 stands for 1992 June 02, or 1992 February 06?? Also what does that "KS" stands for? Does this harness looks like "it's gone" and need a replacement? Thanks

I searched online and seems that replacing the harness could be a DIY project. As we would like to keep the repair cost down as much as possible, so I also "ebay" the part and found some "used" harness for this model (93 300E 2.8). Some quick questions:
  1. Would people recommend buying "used" harness from eBay? why or why not?
  2. If you recommend buying new ones (including OEM?), which online store might have the best price for this particular part? Is there any quality differences between an genuine OEM one and a authentic Mercedes part (does Mercedes even make this part anymore?)

The car runs VERY smoothly on local city roads and highways, it's just that we really annoying that the "check engine light" is on and we can't even clear the light by disconnecting the battery for more than an hour.. Maybe I should leave the batter disconnected for a even longer time, like 8 hours or more? Would that help if it's the harness problem? Thanks again!

Last edited by ohman; 11-09-2010 at 11:23 AM.
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#8 (permalink) Old 11-09-2010, 06:25 PM
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Those wires look pretty good but I don't think you've actually got any pictures of the upper engine wiring harness there. The part number would be either 124 543 90 33 or 124 440 56 32. It runs from behind the battery to the fuel injectors, 3 coils and a number of sensors on the front top of the engine. I think a used harness is a bad idea unless it's really cheap. Parts.com is about $650. But you need to focus on the check engine light - what are the codes, why won't they erase. I'm guessing you're doing something a little bit wrong.
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#9 (permalink) Old 11-10-2010, 11:39 AM
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Originally Posted by deanyel View Post
Those wires look pretty good but I don't think you've actually got any pictures of the upper engine wiring harness there. The part number would be either 124 543 90 33 or 124 440 56 32. It runs from behind the battery to the fuel injectors, 3 coils and a number of sensors on the front top of the engine. I think a used harness is a bad idea unless it's really cheap. Parts.com is about $650. But you need to focus on the check engine light - what are the codes, why won't they erase. I'm guessing you're doing something a little bit wrong.
Hi deanyel, thanks again for your help! Sorry I'm still kind of new as a Merc DIYer, so I'm having a bit trouble to really locate the "upper engine wiring harness." I tried to look for it again this morning in the garage (kind of dark), but still can't really find those two part # (124 543 90 33 or 124 440 56 32). Is that part located in the following picture?



Also I found this article, thought that I would just share it with everyone here:

PeachPartsWiki: W124 Engine Wiring Harness Replacement
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#10 (permalink) Old 11-10-2010, 12:33 PM
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No, wrong side of the engine. You need to be over on the other side behind the battery. There may be a plastic cover over the source plug with the part number. Follow the wires from fuel injectors to the rear of the engine then over to the passenger side rear.
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