OVP relay again? REALLY?!! - Page 2 - PeachParts Mercedes-Benz Forum

compu_85 · #16 11-17-2010, 12:16 PM

Exactly. When / if mine fails I plan on fixing it rather then replacing it. It's a fairly simple device, if voltage goes above the cutoff point of the zener it allows current to flow and pops the fuse.

-Jason

Aquaticedge · #17 11-17-2010, 12:19 PM

I wonder what that little bugger protects, is it just for the OBC (onboard computer) or something more? I know my idle went off (I assume something also with the ELR) and my Tach went plotz too

babymog · #18 11-17-2010, 12:39 PM

In a former life I designed OE automotive electronics, and "load dump" was the most significant damaging event. This is when a large motor or alternator is suddenly shut off, and the magnetic field collapses over the windings causing up to a 60v spike, often reverse polarity.

It wasn't the 603 that required the OVP, it was the electronics in the ABS, ECU, and other electronics. The 603 couldn't car less about voltage spikes, it's mechanical.

babymog · #19 11-17-2010, 12:40 PM

Quote:

Originally Posted by MBeige

Are all OVP relays the same?

No, there are several versions including the 5-pin in the '87 300D and some others up to 9 pins or more with two fuses (mostly gasoline engines).

babymog · #20 11-17-2010, 12:42 PM

Quote:

Originally Posted by JimmyL

My proper MB with an OM617 engine has an OVP relay!!

And yes, I've had to replace it on the '95. Darn, mine only lasted about 177K Mog. You must be doing something I'm not......

My '94s each lost one around 150k, the '95 around 140k (all E320s). My diesels seemed to last longer.

MBeige · #21 11-17-2010, 03:16 PM

Quote:

Originally Posted by babymog

No, there are several versions including the 5-pin in the '87 300D and some others up to 9 pins or more with two fuses (mostly gasoline engines).

Did the diesels receive an updated OVP relay as well?

The M103 OVP, I think, originally had a 7 pin, black top, one 10A fuse relay. The updated version for the same engine has 9 pins, red top and 2 10A fuses.

Now I'm not sure what kind of upgrade was put into the new one that superseded the original (maybe better protection from another fuse). How can it have 9 pins now when the original only called for 7 (or less)?

compu_85 · #22 11-17-2010, 03:25 PM

The extra pins are for cars with extra devices. For example if my SDL had the auto locking diff it would have a 9 pin instead of a 7, the extra ECU gets it's power from the extra pin.

-Jason

MBeige · #23 11-17-2010, 03:30 PM

Quote:

Originally Posted by compu_85

The extra pins are for cars with extra devices. For example if my SDL had the auto locking diff it would have a 9 pin instead of a 7, the extra ECU gets it's power from the extra pin.

-Jason

Does that mean the original OVP and the updated OVP have the same configuration, except that the updated OVP has overlapping applications and does not necessarily use all of the pins?

compu_85 · #24 11-17-2010, 04:02 PM

As I understand it, yes.

-Jason

Jeremy5848 · #25 11-17-2010, 04:35 PM

You might be able to use a newer OVP in an older car if you also had the newer socket and the wiring diagram so you could connect to the correct pins.

As of the 1987 300D, the OVP (K1) protects the Electronic Diesel System (EDS, N39, lives in the little compartment behind the battery and controls EGR, ARV, and idle speed) plus the ABS electronics (both N30, the electronic unit that lives next to EDS, and the electronics in N31, the hydraulic unit).

Jeremy

babymog · #26 11-17-2010, 09:46 PM

It also controls the tachometer and power to the K1? relay for A/C compressor in '87.

pawoSD · #27 11-17-2010, 10:59 PM

My '90 300E had a single fuse original unit, but the replacement has two fuses.

Jeremy5848 · #28 11-18-2010, 11:56 AM

Quote:

Originally Posted by babymog

It also controls the tachometer and power to the K1? relay for A/C compressor in '87.

I'll add a few words of clarification.

Tachometer - The tach doesn't get its power from the OVP but it gets its signal from EDS, which is powered through the OVP. A dead tach is probably the first thing anyone will notice so it's a good indication of an OVP failure. The tach is actually working, it just doesn't have any signal.

Klima Relay - Likewise, Klima isn't powered through OVP. Klima uses the tach signal as its way of knowing that the engine is actually running. It won't allow the compressor's clutch to engage if it thinks the engine isn't running at 600 RPM minimum. In this case, Klima is working and doing exactly what it was built to do. So loss of a/c is another indicator of an OVP failure.

The complete 1987 OVP failure list is:
1. Tach doesn't work
2. Climate control doesn't cool (may not notice in winter)
3. ABS doesn't work and ABS light is on all the time
4. Idle speed is lower than usual (hard to tell without tach)
5. EGR/ARV doesn't work (might be discovered at a smog check)

Earlier and later models will have fewer/more things on the list.

Jeremy

compu_85 · #29 11-18-2010, 01:30 PM

You also won't have SRS, I believe that is powered through the OVP as well.

-Jason

Jeremy5848 · #30 11-18-2010, 02:11 PM

Quote:

Originally Posted by compu_85

You also won't have SRS, I believe that is powered through the OVP as well.

-Jason

Not according to the schematic (page 151). SRS isn't even fused, so that it will always have power through circuit 15R when the ignition switch is on in "Run" or "Start." SRS includes an "energy accumulator" (a fat capacitor) so that it will have power even if circuit 15R is cut in the first milliseconds of an collision.

Jeremy