Oil pressure switches - how do they work?

I'm still looking at the clocks on my Golf. The earth's not the problem, and everything else seems alright, so I'm beginning to suspect the oil pressure switches. The thing is, the computer bit of the clocks doesn't seem to be registering that the ignitions on, let alone that the car's started. One of the signals going into the computer is from the oil pressure switch, and I've gotten to be wondering if the low oil pressure signal you get before you start the car could be used as a wake up signal for the computer. So I decided to have a look at the pressure switch(es), and found it only has one wire.

How does that work then?

Reply to
Doki
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Two wires, the other one is a black one that goes from the battery to the car body.

Reply to
Bobby Secker

It earths itself on the engine.

On my 1 litre Polo, there were 2 oil pressure switches. 1 was normally open and the other was normally closed IIRC.

Reply to
Douglas Payne

Doki ("Doki" ) gurgled happily, sounding much like they were saying:

Ignition switched live feed to the light, then on to the switch. When there's no pressure, the switch is closed, completing the circuit by earthing that feed. The light then comes on.

Reply to
Adrian

On a 2CV maybe, but the OP said that the wire from the oil pressure switch goes to the ECU.

Of course, the principle of your description may well be accurate but might not help the OP.

Chris

Reply to
Chris Whelan

Chris Whelan (Chris Whelan ) gurgled happily, sounding much like they were saying:

Fine. So the ECU feeds the live to the switch, which earths it.

Reply to
Adrian

I'm not quite sure what you mean, but the probability is that the switch circuit is an input to the ECU, and the warning light is an output; there is unlikely to be any physical wiring in between.

On some VW's, the signal from the low oil pressure switch in conjunction with the status of other sensors is interpreted in software as a condition that causes engine shutdown.

Chris

Reply to
Chris Whelan

Chris Whelan (Chris Whelan ) gurgled happily, sounding much like they were saying:

Did I say otherwise?

As I said, the pressure switch earths a specific pin on the ECU's connector, which is fed a small voltage by the ECU. What the ECU does with it, other than kick a light on, I neither know nor care. Never mind VW ECUs - AIUI, many military Landies use the oil pressure sensor to cut the ignition/injection as "squaddy proofing".

Reply to
Adrian

Not the ECU, the computer in the clocks that runs the low oil pressure warning system (below .3bar at idle onwards or below 1.8 bar at above 2000 revs, it'll flash the light, either over 2000 revs IIRC, it'll sound a buzzer).

Reply to
Doki

This is a MK2 Golf we're talking about. I can change a headlamp bulb without difficulty, and the AFM is something you can adjust with an allen key.

Reply to
Doki

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