Ok, its a relay and has a fuse, so its to protect the electrical system / control voltage, it seems like.

What goes through there? I mean from X to OVP to Y.. what's x and Y?

Faulty relay & fuse doesn't, blow yet ovp goes dead?

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1995 E320 smoke silver / parchment

I believe the OVP also has a zener diode.

In short, it's also a surge-protector for the car's sensitive electronics.

:-) neil
1988 E36T AMG
1993 500E

And some dimwit ever decides to jump-start your car with the cables in reverse polarity, you'll be glad you have an OVP!

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Not that I've had much dealings with them, but as far as I can tell they are:

1. Another example of "Let's over engineer something"
2. The root of all evil
3. A practical joke
4. Totally unnecessary
5. A scapegoat to blame every driveability problem on
6. Probably the easiest part to throw at a car by mechanics without a clue
7. A guaranteed source of income for the manufacturer until the last cars with them vanish from the face of the earth

Other than that they're good things to have.

Actually the OVP is quite a device, so simple, so efficient and absolutely a piece of cake to diagnose.

It's simple efficiency assures the worlds two most durable computers the long life they are noted for. I have replaced more GM computers (and I don't work on GM cars) than I have KE controllers and ABS controllers combined.

And if it weren't for OVPs, those who haven't a clue would have to start throwing expensive parts at it right away. Think how much money is saved by throwing an OVP at it first rather than a KE controller.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

If they're so great, then why don't ALL cars have them? And why doesn't MB use them anymore?

Good points. BUT, it would have been nice if the OVP protected the MAS control unit, so a bad AC clutch wouldn't require replacement of the clutch AND the control unit.

I wonder if an in-line fuse in the 12V line to the AC clutch would help.

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2012 E350
2006 Callaway SC560

I believe on another Mercedes list people have placed fuses on the A/C clutch, aux. water pump and mono-valve to keep from "frying" the HVAC/Climate Control unit.

:-) neil
1988 E36T AMG
1993 500E

They don't protect the MAS because they are the MAS. OVPs didn't disappear they just aquired different names and definitely got more complicated. The succesors are variously called MAS, BASE, and most recently are the group of relays called K40/x.

I guess GM never used them because it was easy to throw a controller at a GM car as they are only a little more than double the cost of a OVP (late model) and they failed more often than OVPs anyway.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

I don't have a problem changing OVP's every other month, in lieu of something more serious screwing up, such as ....well any of the expensive $XXX little computers / controller/ modules.... our cars have , this surge that takes our OVP's out? What is up with that? I mean, you are not typically supposed to be changing fuses / relays every other month or year for that matter?

Where's the weak point that takes these OVP's out? I mean, talking "fuses" , for example, if my stereo in the car, takes a fuse out, you know it could just be a fluke, but most likely it is a short somewhere, or the wrong size fuse, or a spike, or...you know I could find , most likely, what caused it to blow and fix the problem so no more fuses...

I am just going to carry a spare ovp and fuel pressure reg.


on a side note, I see how easily a dishonest dealer svc or mechanic could easily ream 1-2-3 mercedes owner's azz when they come in for repair.(AND this is where some might say "oh its soo expensive to maintain.. no sh.it, go pay $859 for a brake job )... NOT saying they are all like that, just the dishonest ones...you know he's got to meet $ quota or has the payment due on the loan for the shop or his pretty little mercedes "next two ovps coming through the door, lets charge them for new cc modules or some other control unit, $1K.." ching ching....

I always blame the OVP as the cause of famine in 3rd world countries....

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

SO how often are u guys replacing the ovp, finally? and the fuel pressure regulator? Or is a fluke ? Nah, they seem to be going on alot of cars regularly, just not sure how often on same cars...

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1995 E320 smoke silver / parchment

Well, I've never replaced either on our cars.....

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2012 E350
2006 Callaway SC560

Never touched my OVP. KE 'puter did take a dump, though. go figure.

I realize this post will result in a blown OVP in the near future.

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'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E

LOL:p Dont blame me for that. LOL ....