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Old 08-02-2003, 05:31 PM
Senior Member
Join Date: Sep 2002
Posts: 2,486
OVP/wiring harness story.................

Well, after one month behind the wheel of my '94 E320(my very first MB)I've come across a few things I'd like to share with everyone. My car was traded in at the MB dealer I work for. The car arrived on a flat-bed due to an intermittent no-start condition. The owner informed the service advisor that if it needed anything expensive he'd trade it in on a new E-class. We already knew the engine harness needed to be replaced. The cracked insulation was noted on several previous repair orders. I spent a few hours checking for simple and obvious reasons for this problem. I should mention that the car started and ran fine every time. I left a fuel pressure guage connected overnight for five straight days. Each morning the guage was checked before attempting to start the engine. No leakage. I tried cold-starts, warm-starts,hot-starts, and everything in between. I monitored several inputs to the HFM/SFI control module simultaneously during cranking(circuits 15, 30,and 31,)via socket box tester, as well as watching several actual values with SDS/HHT. Nothing wrong. Anyway, the owner has fallen in love with the W211. He takes delivery of an 03' E320, so the 124 is mine if I want it. My boss tells me to put a dealer plate on the car and take it home to show my wife and kids. I already know I'm buying this car no matter what. It's exceptionally clean inside and out. I'll deal with the maintenance/repair issues. That night on the way home I stop at the store to pick up a few things. When I get into the car to leave IT WON'T START!!! Finally, I verify the clients' complaint, after all my test equipment has been put away! After a few attempts it starts and runs fine, although the ASR light is on. Great . Now I have some evidence! First thing next morning I check for codes. CAN communication with ASR. No surprise there. I buy the car the that very day and drive it home. I stopped at the parts counter the next morning and bought a new engine harness. I decide to hold off on replacing the engine harness for a few days. I'm not convinced that it's the cause of the no-start. I was able to duplicate the no-start condition several times over the next few days. The OVP was replaced about a year before with the 67 45, but I decided to replace it anyway. Problem solved. I guess even the improved OVP's aren't bullet- proof. So I drive the car for another week and the no-start problem is gone. Although I haven't had any running problems, I decide to replace the engine harness over the weekend at home in the driveway. When I went out to the car early Sunday morning I found the CHECK ENGINE light on. I hadn't yet put the key in the ignition, but the MIL was on. Great. More evidence! When I started the engine I noticed the battery was weak. The ABS and ASR lights were both on, but the engine ran fine. I didn't drive it though. I shut it down and put the battery on the charger. It took me about two hours to replace the harness. When I was finished I turned the key on and noticed the CHECK ENGINE light wasn't on. I cycled the key a few times and it still wouldn't come on. Great. So now I'm thinking the HFM control unit is damaged. I started the engine and let it idle while poking around under the hood to check my work. I closed the hood and went for a nice road test. I drove around for about twenty minutes. Everything's fine, but I'm concerned about the CE light not working. I shut the engine off, wait a few seconds, and turn the key back on. Now the CE light is working as it should. First thing the next morning I clear all codes and it's been fine ever since. I've put a bit over one thousand miles on the car since the harness with no problems. The reason for this EXTREMELY LONG post is simple. I've read dozens of OVP/ Harness posts on this board and realize how confusing they can be to a DIYer. I've diagnosed hundreds of OVP/Harness related complaints and still find new things out. The CE light in my car was "on", but the key wasn't even in the ignition. This was most certainly caused by a short circuit somewhere in the engine harness. I've never seen this happen before!!! The check engine light not working immediately afterward? I've never seen this either. I know this post doesn't shed any new light but I hope it helps people realize the sheer number of possibilities involved when it comes to dealing with short circuits, open circuits, low voltage, poor grounding, internal arcing, etc. Thanks
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Old 08-02-2003, 05:59 PM
Registered User
Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,784
Another thing to mention, while on the CE/code subject..
If one clears the codes , you can not go back to check for "NO Codes " single flash or additional codes UNTIL the diagnostic module has run all its systems test . This takes several drive cycles to complete and until then, there will be NO funtion from the led/sw retrieve procedure....
Same goes for bat disconnect....
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