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Oil Pressure Switch


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My friend is having problems with a 1997 993.

When you turn on the key, the warning lights stay on and

the pressure switch shows high.

He has replaced the instrument cluster and replaced the oil

pressure switch and this still has not fixed the problem.

He thinks that a wire is being pinched to cause this.

Has anyone ever have this problem?

Thanks again for any responses.


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The problem with the car is when you turn on the ignition (engine off) the oil pressure gauge goes to max pressure. We know it is not the sender because we disconnected both wires and still the same problem. We also know that it is not the gauge, tried another and the same problem. So most likely it is a grounded wire somewhere between the gauge and the sender. I also disconnected all wires to the engine so the short is not on the engine. Most German cars usually have the same kinds of problems so if someone else has had this the short may be in the same place. Thanks in advance for any help.
This is my friends explanation on what is wrong with the car.
Thanks for any replies.

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The oil sender consists of two parts:

- a warning contact (green/white wire) which closes to ground if the oil pressure is under a certain limt

- a pressure transducer with following charateristics:

resistance between 5 and 13 Ohm at 0 Bar

resistance between 111 and 121 Ohm at 3 Bar

resistance between 180 and 190 Ohm at 5 Bar

A broken wire between pressure transducer and gauge results in a max gauge reading.

Faultfinding (I assume you have a piece of wire, a multimeter and some resistors )

1)Pressure transducer check

Measure the resistance between ground and point G of the pressure transducer

requirement: 5 - 13 Ohm

2) Gauge check

Connect a resistor of approx 115 Ohm between point II/ 2 of the gauge and ground.

Turn the key (don 't start)

Requirement gauge reading approx 3 bar

with a resitor of approx. 185 Ohm the gauge reading should be approx 5 bar.

3) Wire check

Check the red/green wire between transducer and gauge for continuity

The routing of the red/green wire is as follows;

- from transducer point G


- point 4 of connector X3. You will find this connector in the left hand side of the engine bay in the box with 3 screws cover with the yellow "Danger High Voltage" label.

For recognition of connector X3: at point 1 you will find a 2.5mm2 yellow wire


- gauge point II/2

The picture shows the box containing the X3 connector (picture taken with blower removed)

I hope this will help you!

Regards Hans


Edited by 964hans
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Thank you for your reply.

The oil sender is broken. He bought a new one for over $140 his costs.

He is going to lift the car and then lower the motor. He hopes he can get his

hands up on top of the motor to remove and install the oil sender.

Wish there was a easier way to do this.


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