HFM Control Unit or OVP??? - PeachParts Mercedes-Benz Forum

#1 11-19-2002, 09:53 AM

My wife's 96 c220 won't start. It cranks but doesn't fire; it just turns and turns and turns but doesn't ever spark. I tried everything in the manual about start lock and locking/unlocking with/without the remote/regular key in both the door and the trunk...nothing helps. So I had it towed to the dealership and after checking EVERY wiring point in the car (so they say) they want to replace the HFM Control Unit for $1400 (just for the part). Everything I've read on the site so far indicates it would be the OVP. Is there a way to diagnose one vs. the other? I've read the posts about the different OVP part #'s...when I asked the dealership to check that out they didn't have a clue what I was talking about. Thanks

#2 11-19-2002, 08:28 PM

anybody please have any suggestions? There's a big difference between $50 for an OVP and $1400 for an HFM Control unit...

Mick J · #3 11-21-2002, 08:58 AM

Bad OVP will bring ABS light on in most models. You say there is no spark, does this mean you have checked the fuel pump is operating. Bad fuel pump relay is common.

My '96 E220 will start and run with the OVP removed - your's has the same engine, I would expect the electronics to be similar.

blackmercedes · #4 11-21-2002, 10:06 AM

Quote:

Originally posted by Mick J
...Bad fuel pump relay is common.

Yes it is, and this is a good place to start. A fuel pump relay is also a couple hundred bucks, instead of over a thousand. It's fairly easy to diagnose for the dealer, and if they are on their game, have already checked it. I hope they are truly diagnosing the car (many dealers don't, they throw parts at it).

Quote:

Originally posted by Mick J
...My '96 E220 will start and run with the OVP removed - your's has the same engine, I would expect the electronics to be similar.

Your 2.2L M111 engine is the same as the 2.2L in the W202 C-class. I would guess that most of the electronics are the same, but there may be differences. I would bet that if your car runs without the OVP in place, then his would too.

The HFM control unit is not a pattern failure for the W202.

For starters, you need to talk to the dealer. Ask them what happens if replacing the HFM unit does not solve the problem. Will they refund you the $1400? Will they remove the new HFM unit and put the old one back in, and charge you nothing? What about the diagnosis charge?

At one of my dealers, I took my car on for the very common 722.6 not-as-smooth-as-it-should-be downshifting problem. They diagnosed the problem as worn shifter bushings. Well, I disagreed, but they insisted.

They changed them, and it didn't solve the problem. They refunded me the diagnosis charge and the cost of the parts and labour. I got to keep my new bushings, as it would be too much work for them to put the old ones back in. They would not let you keep a new $1400 HFM unit.

Charles · #5 11-21-2002, 01:12 PM

Hi Mcollie,
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.

Charles

ILUVMILS · #6 11-21-2002, 06:25 PM

OVP's can cause a number of problems. The dealer should know about the 67 45 being the latest/greatest OVP. The 52 45's that are made in Austria are the bad ones. If the dealer wants to replace the HFM control unit, fine. If it doesn't fix the problem they can simply take it back out. Don't let them tell you they can't do it that way either. From time to time I've had to try electrical parts for test purposes( almost always control units for various systems ). This approach shouldn't reflect poorly on the dealership, but installing a $1,400 part at the customers risk and expense certainly should! I've been in this position many times simply because there is no test that definitively points to the ECU as the problem. If they've checked everything that they should have, then they should have several hours into the car at this point. Tell them to go ahead and replace the ECU, but make it clear that you're not paying them if their diagnosis is wrong. This is a perfectly reasonable request. They can send it back if they don't use it, so don't let them tell you they can't. Like I said, I've done it on a number of occasions myself, although I'm happy to say that I've been right alot more often than I've been wrong. Let me know how it goes.

Behind the Star · #7 11-21-2002, 07:34 PM

C220 that will start without OVP in place? Sorry guys but you are going to have a hard time convincing me of that one as it supplies the engine ECU with power (I dont have a wiring diagram in front of me but this is true of the 94 and 95 models and would be very supprised if it was changed for 96).

I have to agree with tkamiya about getting the heck out of there if the technicians at the dealer dont know what an OVP is. I would not be supprised however if the service advisor does not.
I have replaced many overvoltage protection relays causing a c220 to not start. If it is bad it will normally start if you smack the relay with a screwdriver or something. Another tell tale sign is that the Check Engine Light will not come on during cranking but that can be caused by a faulty ignition switch as well.

Look at the side of the OVP. If it was made in Austria...replace it weather its bad or not. Ones that were made in Germany or Hungary are generally OK.

Brian

Mick J · #8 11-22-2002, 03:21 AM

To be fair it is my E220 that starts without the OVP. I don't know for sure that C-class is the same.

#9 11-29-2002, 01:22 PM

Thanks for all the info everybody. The dealership said the first thing they checked was the OVP, even put a new one in right off to see if that was it. There reasoning for thinking it's the HFM is this...the guy says he's getting power to the HFM, but mixed power coming out of it. So that means the ignition is telling the starter to start, it's telling the HFM to start, but the signal from the HFM to the fuel system is not getting through? They did say they would put the HFM in and if it doesn't fix the problem they'll take it back out.

What suggestions do ya'll have? It seems insane to me that a car showing no signs of any electrical problems could just up and not start one day as a result of the central computer all of a sudden croaking. Kind of like somebody just up and getting alzheimer's one day with no prior signs or gradual regressions.

Further, would a bad HFM cause the car to just shut off while driving and then not start like this one did?

blackmercedes · #10 11-29-2002, 02:34 PM

Electrical problems can be very intermittant, and very hard to find if it is a component that has it's "internal organs" failing.

As to it just starting to act up one day, it probably means that a connection that was at the failing point, did.

If it's in the budget, change the HFM unit, and see if it fixes it. BTW, have you looked into alternate parts sources, like this site?