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Old 02-04-2022, 06:55 PM
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Join Date: Aug 2019
Location: Ellicott city, MD
Posts: 170
Testing overload protection relay

Hi, I have a 1986 190d 2.5 non-turbo.

My tach only works when it wants to, about 25% of the time.

I tested the sensor on the bell housing and it tests good.

Is there any way to test the overload protection relay?

I understand that it sends a signal to the tach.

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Old 02-06-2022, 11:20 PM
compu_85's Avatar
Cruisin on Electric Ave.
Join Date: May 2008
Location: Springfield VA
Posts: 5,211
The OVP relay powers the EDS (engine) computer, and several other control units. Does your car idle at the correct speed when the tach isn't working?

1991 350SDL. 230,000 miles (new motor @ 150,000).

Tesla Model 3. 136,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.
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Old 02-07-2022, 01:18 AM
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Join Date: Aug 2019
Location: Ellicott city, MD
Posts: 170
No, it idles very rough and the a/c compressor does not come on. When the tach works, it idles fine but the a/c compressor still doesn't work. I did find a way to check the OVP after hours of searching. It tests as it should.

I started another thread called "rough idle after start up" which ties into this, so I don't want to confuse anyone. Could you have a look through that thread and give me your thoughts? Thanks.

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