OVP's purpose in life is????
 

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?:confused:

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!:eek:

The purpose of the OVP????
 

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.

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.

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.

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 :rolleyes: )... 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.... :eek:

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

So life expectancy is??
 

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...

Re: So life expectancy is??
 

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

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.

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

The OVP is apparently programmed to self destruct after ownership changes. I can't count the times I've heard "Previous owner said he had NEVER had any problems with the car, but two weeks after I bought it the 'check engine' light came on and it began to [ hard start cold, hard start hot, stall, ABS light on, skip, roll over and play dead, etc, etc, etc. ] :rolleyes: Go figure! Of course replacing the OVP doesn't actually fix any of the problems but it certainly sells a lot of OVP's.

That is my question, originally or somewhere on this thread;) . Obviously something is causing it to blow.... changing ovp's is like a bandaid and not really fixing the problem(s) causing it to blow.:confused:

A car is a hellhole for electronics to live in. I read an interesting Intel article some time ago, and the WORST thing that can happen on the +12 line is a "alternator dump", where all of a sudden load get shed quickly, like, from turning your headlights off or the A/C relay kicking on/off (high-current deltas). This puts a spike on the +12 line. Even the battery (acting like a giant capacitor) can't handle it entirely because it can't handle really short pulses (this is one of the reasons to NEVER run your car with no battery or a dead battery).

I THINK (don't know for sure) that the OVP is like a "crowbar" circuit on a switching power supply - that is, when voltage goes over, say, +16 volts, a big SCR (a cheap, high current semiconductor) latches in and presents a dead short - which will then deliberately blow the fuse (and maybe the semiconductor, which is designed to fail shorted). Depending on how the circuit is made, the circuit might NOT latch so the circuit can survive short overvoltages.

This "cheap" (in the relative term) part sacrifices itself (or its fuse) for the sake of other stuff.

Of all the magic MB modules, this one is the most promising to reverse-engineer!

Does anyone know if the europeans use a different OVP in their W201s and W124's? Or is the same part number?

Here is all you ever wanted to know about how the Zener diode in an OVP relay works:

http://www.allaboutcircuits.com/vol_3/chpt_3/9.html

I just replaced the OVP in my SL. It was expensive - $57. I took the cover off and discovered that the problem was that the internal fuse - a piece of meltable wire - had "blown." At least the newer ones have an external fuse that can be replaced!

I examined my OVP yesterday and found nothing suspect inside, looked as new. Have to find another source to the limp mode in hot weather...

Anyway it had a production date of 25.08.93. There were two numbers; one under a MB-star: 000 54067 45 and on the other side it had: 89 7219 000.
My car is sold new in Germany in 1994.

Thats for a W202 right?

No, it is a W124, or rather C124, the E 36 AMG Coupé. Same engine as the C36 though...

Post some pictures of your W124 E36 (engine, tranny, etc.) and some specifics (calipers, tranny, diff ratio, etc.).

My W124 wagon has the C36 engine in it.

I'd like to see what's different.

:-) neil

Hi, I have just a few pictures of the engine, nothing else, but I can take some more in a couple of days...

That's an excellent description. The OVP's purpose in life is to protect the electronic control units. If the voltage goes too high, the zener conducts causing the fuse to blow.TV electronics use spark gaps around the picture tubes to protect it from voltage spikes.

It's the sacrificial anode of our cars.

Funny stuff, Cap'n. Worth resurrecting an old thread.

My diesel idle speed control (ELR) wasn't working until I changed the OVP relay. The OVP fuse was intact, and there was nothing obviously wrong inside. I do not know how to test the individual components on the circuit board, but nothing was burnt or broken. I would conclude that it is entirely possible for the OVP to fail without any apparent physical indication.

Very easy to diagnose. The actual schematics for the circuitry is right there on the case, it can't get any better than that;)
My first encounter with the OVP (when I had no clue what it was) was when I first got the 560SEL (did someone mention it usually timed to ownership change?:D ) the ABS light was on and the car would idle high.

Intermittent problems
 

On startup, the ABS light is off, and presumably all the circuits downstream of the OVP are happy [e.g. the ABS stuff works].

Hit a rough spot in the road [it doesn't always take a big bump] and the ABS light comes on. I'm interpreting this as a bad connection, either in the socket or in the wires connected to the OVP relay socket. Are any special tools useful to recrimp the connectors in the socket?

Judging by the instructions in the service CD for the W124, the OVP is secured in its bracket by a bolt, so it should be good and tight in there, unless the bolt is loose or missing. Should be the same on your 89.

Common problem with the OVP relay is cracked solder connections on the printed circuit board, so hitting a bump in the road can cause an intermittent OVP relay to act up.

Technical OVP testing employs the standard Benz "Tappity-Tap Test.".
This is done with a light tapping of the OVP in situ with a screwwdriver handle when the condition exist... However , this tapping does have to be done to a specific rhythm /meter..
" Lord, won'tcha buy me..a.. Mer ..Say...Deys ..Benz, ....Oh Lord.. wont'cha buy me... aaaa mer..cedes.. benz.. ???? "
....with a kinda Blues feel , shuffle beat.........

Man this is raising an old one
 

I talked to Cap'n last week and he is doing good and seems to be enjoying life.

Just for kicks I went out and grabbed a snapshot of the OVP in my '95 E300. Hopefully I will get it back together this week. I may need to replace it. The cruise is not working and I have not been able to do any troubleshooting on it. All you have to do to remove this one is "roll" it up counterclockwise while pulling the left tab out. The tab is at the left of bottom center in the pic.

The camera did a good job with it being dark and all - Casio Exilim. I struggle with taking good pics like this.

Hi y'all,
Is there an OVP on a 1988 300 SE, and if so, where would it be. My car is getting to be hard to start. Seems to be mostly when warm, but not always. This morning's temp here in Texas was about 49- 50 degrees f, and it did not start as quickly as it did at 35 degrees a couple of days ago. And this afternoon, with weather of around 75 was hardest to start, but after normal operating temp started immediately every time. Any Clues?

What I have on the '89 is a hard plastic bracket attached to the inner firewall, behind the battery. A strip of aluminum that's part of the OVP provides mounting 'ears' that fit into the bracket - no screws on the OVP or any place for them on the bracket

You're absolutely right, works the same on my '88. Not the first time that the FSM instructions were either wrong or applied to some other chassis than the 124 without noting it.

I am trying to diagnose wipers not working. As soon as I turn on washer/wipers they kick out along with the windows and rear seat recline stop working. They came back operational after fifteen minutes or so.
Manual says the wipers are overload protected. Could this be the same OVP relay failure?
Thanks in advance for any advice.

Rando
1988 560SEL

OVP? Finally a cause for all problems. Now we can retire "second hand smoke", "global warming" and "George W. Bush" as the source of all the worlds ills!
Anziani