I recently fitted a new oil pressure switch to my 1.4 6N1 8valve APQ engined Polo. The old switch was leaking oil.

I went for e Febi Bilstein switch, but after fitting, the oil light would flash after the revs hit 2K

I thought that the old switch had not been working correctly and that I had an oil pressure issue which I attributed to the pick up pipe getting clogged.

Off with the sump. Off with the pick up pipe. Gave it all a thoroughly good clean. Got lots of sludge and crud out and put it all back together.

Fired it up and still the same.

So I thought, worn out oil pump.

Got an oil pressure gauge and it's about 2 bar at idle rising to 5 bar at about 3K . So it appears that the oil pump is still good.

So I thought, faulty switch and ordered a Bosch one. Just fitted it and it's still the same. Starts flashing as the revs reach 2K ish.

Once the engine has warmed up, it doesn't stop flashing when it returns to idle, but it does stop flashing at return to idle when the engine is cold.

 

There is no rattling or any other symptomatic noises of low oil pressure when the light is flashing.

 

Could it be the wire for the switch ?  I'm all out of ideas as to what it could be.  Any helpful input very gratefully received.

Yes, we'll worth checking the wire. If I can find relevant circuits I'll try to find where it originates for you, tomorrow. 

Tends to be the instrument cluster, I think, in this era.

 

Thanks Pete.

So I'm guessing that the switch is closed and earthed in its non pressured state and the oil pressure opens it, disconnecting the earth and turning the oil pressure light off ?

If there was a break in the wire, that would mean no earth and oil light permanently off ? Or is it the other way round ? The oil pressure closes it to earth ?

I looked at the wiring diagram in the Haynes manual and it says a yellow wire to connector 10 on the instrument cluster.

 

Is there a test I can do without having to tear the dash apart ?

 

What is the thinking behind the shroud on the sieve for the oil pick up ?

I was reading about someone who had a similar problem and ended up cutting the shroud off the pick up sieve which sorted the problem out.

 

I think I'll check the oil pressure again, just to be sure.

Edited 15 February, 20242 yr by Polo3

They're usually normally open (non-conducting to earth) when below their threshold pressure, and short the wire to earth once it's above the threshold. 

That way a broken wire shows as a fault, as a failsafe.

Remove the wire and measure the pressure switch terminal to earth with a resistance meter, engine off and engine running at say 2k rpm to check if yours does this (or the opposite).

 

Instrument cluster isn't usually very hard to get out far enough to access wiring connector(s); but I don't have relevant 6N1 experience.

 

From the spade connector to the switch body is continuous with the engine off, with a resistance of 001

With the engine running, no continuity and a consistent resistance reading all through the rev range. So it appears the switch works.

Checked the state of the wire directly above the connector. It's intact and connected. It's also black, not yellow.

The connector was not that tight so I pinched it up a little. When I started the engine after doing this, it would rev to 3.5 - 4 K before the light came on and then it would turn off again when dropping back to idle. It wasnt doing this before. So tightening the connector seemed to have an effect.

It's a bit of a clue, but I cant figure it out.

Maybe the wire could be partially broken somewhere along its length ?

What do you reckon Pete ?

From the connector on the pressure switch the wire goes through 3 more connectors, the main engine disconnect down by the thermostat housing, then into and out of the central electric connectors behind the dashboard and then finally to the speedo connector.

To remove the speedo drop the steering column to its lowest position then look into the hood over the speedo and you’ll see two round blanks, remove them and the screws behind them then pull the hood/surround away then if you look in the top right & left corners you’ll see Torx screws with these removed the speedo unit can be tilted towards you and the connectors can be removed, there’s no problem with it needing any diagnostic kit when you refit it 

Cheers Nige.

I forgot to mention that I disconnected the oil pressure switch and fired the car up. It behaved exactly the same. Oil light off until about 2K

I cant understand why it never did that before I put a new switch in. Maybe I broke the wire whilst changing it ? I'll bypass that first section to the big plug.

Did you fixes this issue as I have my sisters AUA doing the same thing?