# Troubleshooting Oil Pressure Switches - Wiring Diagram



## 7rrivera7 (Jun 24, 2010)

Ok , i've done all the appropriate tests for the low and high pressure switches and they are funcioning properly but I get the oil ressure light and buzzing when I rev past 2000 rpms. Since the swithes were validated as working by design using a test light, I need to test continuity and the high pressure wired but I dont know if it goes to the cluster or the ECU.

I'd like to attach a wiring diagram from my Bentley where the switches are labled F1 & F22 but can't for some reason and would appreciate if someone can tst me how to read it or where to find the other end of the high pressure switch wire to make sure it has continuity.

Thanks!


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## cuppie (May 4, 2005)

7rrivera7 said:


> Ok , i've done all the appropriate tests for the low and high pressure switches and they are funcioning properly but I get the oil ressure light and buzzing when I rev past 2000 rpms. Since the swithes were validated as working by design using a test light, I need to test continuity and the high pressure wired but I dont know if it goes to the cluster or the ECU.


 Neither do we - we don't know what you're working on!  
Year, model, engine? 
Helpful tip: Put your car in your profile, so we all know what you're working on. 



> I'd like to attach a wiring diagram from my Bentley where the switches are labled F1 & F22 but can't for some reason


 Because nobody can - you need to host them off-site.
*How do I add an image to a post?*


> and would appreciate if someone can tst me how to read it or where to find the other end of the high pressure switch wire to make sure it has continuity.
> 
> Thanks!


 Not a problem, once we know what model you're working on.


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## 7rrivera7 (Jun 24, 2010)

Car is a 1996 2.0 Cabrio 5 speed. The test I performed was verifying the electrical status of the oil pressure switches with a test light as follows:

1) Car OFF, low pressure switch (blue on cylinder head) is at GND
2) Car ON, low pressure switch goes HIGH
3) Car OFF, high pressure switch is HIGH
4) Car ON, high pressure switch is HIGH until the engine warms up then slowly goes to GND. If I rev the engine after warmup, the high pressure switch will go HIGH until I let off the gas.

According to the Bentley and other sources, the switches are responding correctly. The problem is that when I rev over 2000, the oil pressure light and buzzwer come on.

If I GND the high pressure connector while it is NOT connected to the switch, this should allow me to rev without the light or buzzer coming on byt they come on anyway which is the reason I want to trace the high pressure switch wire to make sure it has continuity to it's destination which I'm not sure is the ECU pr the cluster.

Here is a link to the wiring diagram: https://drive.google.com/file/d/0B_WDOgIVK1DYV3U0NWZ6d0NCY3c/view?usp=sharing


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## cuppie (May 4, 2005)

I don't remember if the switches on that car are wired to the instrument cluster, or to a relay. 
See the *b* and *c* lines in the grey area at the top of the diagram? Trace those thru the book, until you get to the other end of them. That's what the switches are wired to. 



> 4) Car ON, high pressure switch is HIGH until the engine warms up then slowly goes to GND.


 That isn't right. It's an ON/OFF switch - it shouldn't vary in resistance like that. Minimally, the high-pressure switch is faulty. 

Got a DVOM? Disconnect both switches, and turn the key ON. You should see ~12v on each line. If you do (and, it sounds like you will), then the wires are either: 
1- OK, or 
2- shorted to B+ somewhere downstream of their control unit. Disconnect their control unit to see which it is.


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