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no oil pressure light

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I've got a bit of a problem in that I have no oil pressure light after refitting the head.

I obviously don't want to start it until I know that I have oil pressure.

I have 12v at the switch and 12v at the blue and black wire on the dash connector but don't have a light when the switch is earthed or not.

Any ideas?

I assume that it should earth through the switch when there is no oil pressure and give 12v when there is?

If not should it be earthing through the bulb, in which case which colour wire is that?

I have ignition and handbrake lights.

Thanks in advance.

Simon

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The oil light on a MK1 golf is more than just a light, there's some circuitry that goes with it and two pressure sensors on pretty much all engines (as far as I'm aware.)

These sensors work in conjunction with each other, as well as picking up the engine speed and whether the engine is running or not to decide whether or not to illuminate the oil light, it's not simply earthed through the light as it might be on most other cars.

Mike.

1983 White cabriolet GTi - daily driver now with new cam belt. :-)
1992 Mitsubishi Delica Chamonix 2.5 Turbo Diesel - currently broken.

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hmm, it used to work ok before I took the head off. I wonder if it the circuitry is not earthing correctly. Presumably it's the tag on the rocker cover that earths it, then through that and the chassis to the battery?

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After having a quick read, it sounds like there is a standard oil pressure light which presumably should work when earthed, and an oil pressure circuit that operates at above 2000rpm and operates a buzzer.

Is this correct?

It's the little yellow oil pressure LED, which I believe is the standard one that currently doesn't work.

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It operates the buzzer AND light.

The basic operation goes something like.

Ignition on but engine not running - light flashes as a 'test' but only if connected to the primary oil pressure sender which is a normally CLOSED circuit.

Engine running at IDLE, light goes off if primary oil pressure sender is OPEN (i.e not earthed) If it is still CLOSED then light stays on AND the buzzer sounds.

Engine running above 2000RPM light stays off if primary oil pressure sender is OPEN and secondary oil pressure sender is CLOSED as the secondary oil pressure sender is a normally open circuit I believe (thus disconnecting the secondary sensor usually makes no difference to the operation of the circuit, it just removes the secondary level of protection)

I've just had to replace the little logic circuit in my clocks as it totally failed and started sounding the buzzer all the time, even without the engine running, this is the circuit that controls it all.



It's hidden behind the speedometer.

Mike.

1983 White cabriolet GTi - daily driver now with new cam belt. :-)
1992 Mitsubishi Delica Chamonix 2.5 Turbo Diesel - currently broken.

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I see, interesting. so the primary oil pressure switch should be normally closed, therefore reading gnd at it's terminal.  I am seeing 12v (I assume this is the one on the front of the block on the top of the oil filter housing?)

I don't see any change in behaviour if I earth it though. I assume that the logic circuit/buzzer is fused, if so where?

It must know that the engine is running? Presumably this is a signal from the coil or the TCI?

Are these still available or did you have to repair the circuit?

And finally (sorry for the questions) do you know of a circuit diagram or debug procedure to check that I have the right voltages on the right wires going in and out of the dash?


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The circuit is part of the instrument cluster, it's powered from the same +12v as the other instruments.

I brought a second hand set of clocks off e-bay and chanced that the circuit would be OK on them and it was, it's a pain to get to thou as you have to strip down the entire cluster.

If you get a multimeter and test between the +12v on the battery and the output on the primary sensor you should see +12v with the engine off and 0v with the engine on, i.e the switch is closed with the engine off and open with the engine on, this is the normal operation of the switch as far as I can remember.

I forgot to check that your engine has the same switches as mine, mine is a single wire switch, but there are variations which have two wires I believe and work as a proper switch rather than switching the terminal to ground.

1983 White cabriolet GTi - daily driver now with new cam belt. :-)
1992 Mitsubishi Delica Chamonix 2.5 Turbo Diesel - currently broken.

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the oil buzzer wont sound at idle, it only buzzes over 1.8k ish rpm.

basically it works like this, if oil pressure drops below 0.3bar and revs are below 1.8krpm (or whatever the high pressure circuit changeover is) then the light will flash. over that the light will flash and buzzer will sound if the oil pressure drops bellow 1.8bar

the reason the light flashes with ignition on is simply because the oil pressure is below 0.3bar, as funnily enough the oil pump doesn't produce any oil pressure when the engine is not turning over ;)

does everything else on the dash work with the ignition on such as fuel gauge, mfa, coolant & battery warning light etc?

Hello my name is John and I'm a dub addict.



My wiring diagrams and other documents have moved here:

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After doing some more research my first port of call is to look at the low oil pressure switch on the head. I thought the primary one was the one on the oil filter housing, but this is the higher pressure one isn't it?

 :P

First thing to do is to test that the primary pressure switch works!

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And yes, everything else on the dash works. Although it does look like it's not earthing correctly because, even though everything works the illumination lights are very dim and the indicator light glows dimly all the time suggesting that it is earthing through the wrong circuit.

S

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yep the low pressure switch is the one in the side of the head, try earthing the spade see if the light comes on?

if the clocks have the MFA the main earth is to the side of the head, look for a brown/white with a ring terminal.

also make sure the gearbox earth is good, if you suspect engine earth put a jump lead between the battery -ve and the engien block somewhere that'll rule it in or out straight away :)

Hello my name is John and I'm a dub addict.



My wiring diagrams and other documents have moved here:

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As you're reading the posts at the moment, can I ask a cheeky question before I look, where physically are the gearbox earth points and the chassis leg earth points?

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the chassis leg one is about half way along, the gearbox one should be to a stud on the upper gearbox bracket. its a poor design by vw as corrosion builds up between the box and bracket.

on later mk2s and mk3 the engien earth is moved to a stud on the rearmost engine -> gearbox bolt which is much better. if you have a decent scrap yard local i would pinch all the battery and alternator cables from mk3 1.8-2.0 as they're better design and thicker. you'll have to make up a lead from the chassis leg tho as the mk3 oner wont reach. all i did was get 2 mk3 -ve cables and chop the 2nmd one down so i had 2 ring ends, ran 1 to chassis leg and bolted the other to the 1st mk3 cable where the middle ring is if that makes sense

Hello my name is John and I'm a dub addict.



My wiring diagrams and other documents have moved here:

VAG Documents & Downloads

You'll need to sign into google/gmail for the link to work! (its free!)

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Thanks, I'll take a look at them tonight.

Cheers

Simon

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OK, it looks like it might be the dash somehow.

Earthing the oil pressure switch doesn't make any lights come on the dash. Is the oil pressure light fused at all?

Also, while cleaning up the earths I unearthed (sic) an unconnected 2 pin connector going into the loom under the expansion tank. One wire is brown, so presumably an earth, the other what looks like white when cleaned up. It's one of the clear plastic 2 spade connectors with the two spades at right angles and is obviously original. I can't see anything to connect it to though.

I love old cars, the more you look at the more you find that has been bodged and badly maintained! I keep thinking I must have found most of it on this one but keep finding more!  :dry:

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Also, is there a good schematic of the oil pressure circuit behind the dash (at least the connections to it), I think the next place to look is there.

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What I refer to as the primary pressure switch is the one on the oil filter housing; noting your post above. Earthing this should cause the light to come on, and with the engine running it should also sound the buzzer. - EDIT sorry got that wrong, it's the one on the side of the head, my fault.

That 2 pin connector under the header tank, I wouldn't worry about as my car has the same. It's for an option which wasn't fitted, but the wiring is present for. I've often wondered exactly what it would be used for thou.

Last edit: by Maniac


1983 White cabriolet GTi - daily driver now with new cam belt. :-)
1992 Mitsubishi Delica Chamonix 2.5 Turbo Diesel - currently broken.

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This page Mk1Vw - Tutorials describes the operation of the circuit better than I can. I always get confused between sensors and open and closed circuits - it was what I followed when I was looking at similar problems with my car, but I've only just found it again!

1983 White cabriolet GTi - daily driver now with new cam belt. :-)
1992 Mitsubishi Delica Chamonix 2.5 Turbo Diesel - currently broken.

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Thanks for the link, I've had a quick flick through, I'll work through it tomorrow night.
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