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W201, W202, W203, W204, W205 Moderator
Amethyst 2001 C320
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Discussion Starter #1
As requested by several people, here's a short DIY to repair your engine wiring harness so you don't have to spend $800-$1500 to replace it.

Take the cover off where you would replace the spark plugs to see the three wires (on a C280) that lead to the 3 coils. These wires are 12V DC, and are the most common failure points.

Picture 1 is a view of the part of the harness on my car that failed. Carefully cut off the outside insulation of the harness between the plug and where the harness enters a rubber section.

Picture 2 is a view of the harness after I removed the outside insulation. The picture is kind of fuzzy, but you can see the green corrosion on the wires and how there is no insulation around them...this is bad!

Picture 3 shows how I separated the wires and wrapped electrical tape around them, and then wapped more tape around both wires to hold them together. Be very careful to separate the wires entirely, especially in the plug and in the rubber housing.

Connect everything back up, making sure to have the air tube that crosses over the engine back in place, and then start her up. She should fire on all cylinders now, but if she doesn't then just jiggle the two wires around a bit near the plug and rubber until it works.

Last step, to reset the Check Engine Light, turn the engine off and pull fuse number 32 in the fuse box on the driver's side of the car (LHD cars), and leave it out for about 30 seconds. Replace the fuse, turn the car on, and the Check Engine Light should be off.

Good luck!
 

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2001 E320; 2002 ML500
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The engine wiring harness suffers from a cracked insulation in several places, including connections to the ECU. You're better off replacing the darn thing.

Sergio
 

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W201, W202, W203, W204, W205 Moderator
Amethyst 2001 C320
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Discussion Starter #3
Sergio said:
The engine wiring harness suffers from a cracked insulation in several places, including connections to the ECU. You're better off replacing the darn thing.

Sergio

Note: This guide is intended for those who don't want to or who don't have the cash for replacing the harness at a cost of $800-$1500 for the part alone. Although replacing the harness is best, it's not always a feasible option.
 

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But you run the risk of damaging the ECU and other electrical components.

Sergio
 

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W201, W202, W203, W204, W205 Moderator
Amethyst 2001 C320
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Discussion Starter #5
Repairing the harness in the way I described won't put your ECU at risk. In fact, you're more likely to protect your ECU by performing this repair, rather than just leaving it broken (with the wires shorted out and the cylinders misfiring).
 

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I just changed the wirring harness for my c220, but the car still displays the same kind of rough idle it had before. I thought this would fix it. What else could it be?
 

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W201, W202, W203, W204, W205 Moderator
Amethyst 2001 C320
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Discussion Starter #7
mbblues said:
I just changed the wirring harness for my c220, but the car still displays the same kind of rough idle it had before. I thought this would fix it. What else could it be?
Your MAF sensor may be bad. There's a couple recent threads in this forum about how to replace it.
 

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2001 E320; 2002 ML500
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I don't mean that doing this repair could damage the ECU; what I mean is that leaving the bad engine harness in place could damage the ECU so even if you perform this repair, there are other areas of the harness which still have problems so the best bet is to replace the entire harness.

Sergio
 

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Wiring Harness

I just got a quote to replace my harness for 1508.00 from a MB dealer here in the Toronto area... I think I am having the same problem...Sometimes the engine runs real smooth and at other times seems like it is missing on a couple of cylinders and has absolutely no power... Does this sound like the same problem to you and if so can an average guy (pretty mechanical) take this apart and fix it..

Pete
 

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W201, W202, W203, W204, W205 Moderator
Amethyst 2001 C320
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Discussion Starter #10
It is possible, as demonstrated by my photos, to repair the harness without replacing it. Unfortunately most dealerships are no longer offering "goodwill repairs" on the C-Class engine harness, so a temporary repair as per my instructions will work.
 

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I spent a week trying to find a decent harness for my 95 C280 but ended up buying a new one from a MB dealership several months ago. I am in Houston Texas and it cost about a grand for the harness. I was told by the MB dealership where I bought the harness that these cars came off the line with defective wireing harness' and many MB dealerships did replace them at no charge for several years. I just waited too long. I also had a ton of other work done at the same time. Fuel filter, plugs and wires, tune-up, belts, etc. All in all it came to $2300. I hope it was worth it. The car is cherry as far as looks go. I just bought a fan clutch off eBay for $99 because I know that will go out next according to my mechanic and I noticed just as he said, the temp now runs at 100f instead of the 80f I am used to seeing. Strangly, I was getting 31MPG on the highway (air off) before the tune-up but now get only 29MPG. Go figure.
 

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Hi, I would like to point out that waether you can afford it or not one must replace the whole harness once it gets to that stage. If the insulation is coming apart at the coils then it will be bad all over the entire harness including inside the rubber mouldings under the coild/plug lead cover. You don't wont to have to replace the computer if money is the object. I tried following your advice to repair it as per your photo's but it goes much deeper than just their, my advice is borrow the money save your car and replace the harness.
 

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W201, W202, W203, W204, W205 Moderator
Amethyst 2001 C320
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Discussion Starter #14
davi2 said:
Hi, I would like to point out that waether you can afford it or not one must replace the whole harness once it gets to that stage. If the insulation is coming apart at the coils then it will be bad all over the entire harness including inside the rubber mouldings under the coild/plug lead cover. You don't wont to have to replace the computer if money is the object. I tried following your advice to repair it as per your photo's but it goes much deeper than just their, my advice is borrow the money save your car and replace the harness.

That's true, the chances for success on this repair depend a lot on your skill level with wiring.
 

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Wiring Harness Problems

Cut and paste this website in your browser you would be amazed at the problems being caused by these faulty wiring harnesses!

Gas leaks, wires shorting, engine fires!

I need to replace mine, over a four day period one tank of gas which usually yields 370 miles, ran out of gas at 155 miles. Realized I had a leak, had the car towed to the house. SRS is malfunctioning, engine surging, fuel guage not working. Car has only 73,000 miles and it has been kept up immaculately, no engine dust. I am a little hesitant to just repair it at this point but I do not have an extra $1,500 laying around to replace it. :eek:


http://users.adelphia.net/~infoage1/complaints_nhtsa_mercedes_wiring_harness_failures_1991_1997.html
 

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Bottom line here is that Mercedes never did a recall, and the number of cars affected is unbelievable - years 91-97 all models. Cars stalling on the freeway, fires...what happened to safety???
 

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1986 190e 2.3-16 (W201), 1997 SL320 Panoramic Glass Top (R129) & 2009 C300 Panoramic Top (W204)
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Take a stand!

Has anyone heard about or thought about making a class action case? :mad:
 

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W201, W202, W203, W204, W205 Moderator
Amethyst 2001 C320
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Discussion Starter #18
I think the fact that it affects so many cars is precisely the reason why they never recalled it on their own. And since nobody ever persued it with the NHTSA, MB wasn't forced to recall it either.

Since we're talking about cars that were built 10-15 years ago, I highly doubt that the NHTSA would do anything now, much less MB voluntarily recalling it themselves.

It's a bummer, really. I still like Mercedes, but the next one that I buy will be a 1998 or newer.
 

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Did it !

Made a new harness for my C-280, used the original connectors, spliced the wires (automotive heat ressistent) next to the plugs (connections) with solder and heat shrink tubing, took about 4 days to complete the project, car started on the first try, no trouble codes present, car is performing GREAT, car now has a steady idle of 550 rpm. Moral of this story ? You can DIY !
Ed

Removing the old one:



It's Off:



Repairing : Top of picture, Injectors and Coil plugs (red wire) repaired.



P.S It's important to take many pics, it helps solve repair and installation doubts !
 

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W201, W202, W203, W204, W205 Moderator
Amethyst 2001 C320
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Discussion Starter #20
Wow, that's awesome! Would you consider offering a harness rebuild service? I would be interested in being your first paying customer.

It would also be cool to know what brand and guage of wire you used, as well as the name of the company you bought it from.

Also, do you have more pics that you can post?
 
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