Re: HFM Control Unit or OVP???
I have same problem more than a year ago. Here is what I did to temp fix it.
This morning my 94 C220 just won't start, the battery, starter are all OK. No matter how I crank the starter there is no any sign of engine combustion. I think the problem should come from electrical firing system and the first one on my mind is the famous OVP relay. Story back to March this year when I had my engine wiring harness replaced, the dealer recommend me to replace the OVP but I did not. Because My OVP's date code is 050996, part # is 000 540 67 45. I thought this is an updated one.(I bought my car last year). This morning's problem proves I was wrong at that time.
OK, continue. First I use a multi-meter to measure pin #1, it got 12V, good! Pin #2, no voltage appears. From the diagram on the side of OVP, Pin #2 in activated by K3 replay. TO be safe I consult my mechanic uncle he said he used to have this problem on a E220 which failed at Pin #2. I can temporarily jump pin #1 and Pin #2 to provide pin #2 voltage. I did and it started, wonderful! Then I drove to a nearby mechanic to order a new one. The new OVP is exactly the same as the failed one, part # is same and also made in Hungary, except date code is 011000. I think it's made in year 2000.