My mechanic just called and told me that there are 3 Overvolt relays... which one should I have him replace?

There may have been 3 different upgraded part #'s , but the car has only one OVP Relay.

There are so many threads about the OVP that if a comprehensive document was written, the forum would be better of offering it via CD-ROM on FastLane or PartsShop.

As far as the part number issue, the old defective OEM unit says Siemens Austria on the side, and is part number 000-540-52-45.

Part number 000-540-67-45 is the "corrected relay you want.

Fast Lane has the OVP for about $50, but it sounds like you already have the shop working on your car.

The OVP issue is probably a new topic for you newer members, but for the rest of us, it's like listening to a old Bee Gees record over and over and over...

Use the search link and use OVP as the keyword. The resulting threads presented for your reading pleasure will give you hours of fun! You will know more about the OVP than the engineers who designed it!

But think about how proud you will be when the next new member has a problem with hot starts, etc. You can confidently reply that he/she needs to "replace the OVP". Of course, then he/she will ask, "can you tell me what an OVP is, and how it works?"

And so on...

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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

I agree with G-Benz. You could fill volumes with what's been said about the infamous OVP.

I believe I've read here that the older versions had a single 10 amp fuse and the current versions feature dual fuses. Correct me if I'm wrong.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

There are 3 different OVPs to cover all the different models that use them. Just as each car has a different alternator. The number mentioned fits cars with HFM fuel systems which the 90 model doesn't have.

The other two numbers are 201 540 08 45 and has one fuse and 201 540 37 45 which has two fuses. The 08 has 5 pins and the 37 has 9 pins. The originals OVPs might have one less pin on each. All the relays have been updated to these current versions.

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