electrical gremlin, OVP relay?

[vikingGoalie]

So the symptoms all seem to be related.


If it's cold, and the ABS light stays on, then...
engine idles a little rough until it's warm.
tachometer doesn't move and stays on zero.
the climate control system only blows hot air, and the center two vents don't blow at all.


If the ABS light goes off (happens intermittently, ABS light can go off while driving) then all of the above start working normally.

Some reading i had done previously led me to believe the OVP could be the culprit as the other poster was talking about the ABS and Tach.



Otherwise the car runs fantastic, and even with the ABS light on once it's warmed up runs just fine. The OVP relay is not part of any mounting piece, it's loose in there so I'll have to remove the battery to get at it. But it's most likely NOT a fuse as it works fine some times and other times not. So that makes me wonder if it's a loose wire gremlin or some such.



thoughts? suggestions?
thx!

[Diseasel300]

Ms. Cleo does not work here. What year and model are you working with?

[vikingGoalie]

1993 300D, 212K miles. Sorry i thought it was in my profile/displayed but i was wrong

[Diseasel300]

The OVP relay feeds the EDS computer and the ABS system, so those two systems do indeed point to an issue with the OVP relay. The EDS computer sends the tach signal to your tachometer and also controls the idle speed. When the OVP relay is bad, the IP runs on the default mechanical idle stop ~500 RPM and can run rough if the injectors need service or the compression isn't the healthiest.

The climate control issues will be a separate issue. The climate system does not run power through the OVP. There are a huge number of possibilities for a fault, if the system thinks it should be heating though, no air through the face vents is normal.

[vikingGoalie]

Originally Posted by Diseasel300

The OVP relay feeds the EDS computer and the ABS system, so those two systems do indeed point to an issue with the OVP relay. The EDS computer sends the tach signal to your tachometer and also controls the idle speed. When the OVP relay is bad, the IP runs on the default mechanical idle stop ~500 RPM and can run rough if the injectors need service or the compression isn't the healthiest.

The climate control issues will be a separate issue. The climate system does not run power through the OVP. There are a huge number of possibilities for a fault, if the system thinks it should be heating though, no air through the face vents is normal.

thx!. and after i posted this today the climate control was working right, and the abs/tach were not. so yea seems like a seperate thing. To my one question on the OVP, can it be intermittently bad?

[Diseasel300]

OVP relays frequently fail in "intermittent" ways. Buy a new one from the dealer. A used one is just more BS waiting to happen. It's been suggested that they have an average lifespan of 10 years give or take before they go goofy.

[Frank Reiner]

Originally Posted by Diseasel300

OVP relays frequently fail in "intermittent" ways. Buy a new one from the dealer. A used one is just more BS waiting to happen. It's been suggested that they have an average lifespan of 10 years give or take before they go goofy.

First! Check the fuse(s) on the top of the relay.

[vikingGoalie]

the fuse looks intact.
Am I asking for trouble getting the part here: https://www.eeuroparts.com/Parts/70338/Overload-Protection-Relay-2015403745A/

I mean dealer wants $88 for a relay, that one is $18. But just wondering if anyone has experience with aftermarket OVP relays...
tx