540 V8 No OIL pressure light please help!

[ben wilamowski]

Hi everyone,

I have just bought myself a 540 V8 auto and am loving it but I want to get her absolutely right as this car will be a keeper, I have just noticed one thing which fills me with a bit of dread.

I cannot get my low oil pressure light to come on when I start the car.
I understand this should come on with all of the other warning lights and go out when the engine starts but mine does not do anything at all.

It looks like the low oil pressure sensor was bypassed by someone in the past and the wire was connected directly to the alternator instead.

I have now reconnected what I believe to be the sensor wire to the oil pressure sensor and replaced the bulb in the instrument binnacle but it still doesn't light up.

I do not think there is a problem with the engine as I do not get a low oil pressure warning from the check control computer and she goes like a train with no funny noises and absolutely no smoke under any conditions even full bore acceleration.

I guess the next thing is to replace the sensor itself, but surely if it was faulty the light woudl still come on but not go out!?

Can any body suggest what I should check now......

Best regards

Ben.

[ryan roopnarine]

there is a wire that should go from the alternator to the battery light in the dashboard, are you sure you are not mistaken?

Hi everyone,

I have just bought myself a 540 V8 auto and am loving it but I want to get her absolutely right as this car will be a keeper, I have just noticed one thing which fills me with a bit of dread.

I cannot get my low oil pressure light to come on when I start the car.
I understand this should come on with all of the other warning lights and go out when the engine starts but mine does not do anything at all.

It looks like the low oil pressure sensor was bypassed by someone in the past and the wire was connected directly to the alternator instead.

I have now reconnected what I believe to be the sensor wire to the oil pressure sensor and replaced the bulb in the instrument binnacle but it still doesn't light up.

I do not think there is a problem with the engine as I do not get a low oil pressure warning from the check control computer and she goes like a train with no funny noises and absolutely no smoke under any conditions even full bore acceleration.

I guess the next thing is to replace the sensor itself, but surely if it was faulty the light woudl still come on but not go out!?

Can any body suggest what I should check now......

Best regards

Ben.

[simon-york]

It is an old dodge by some to connect the oil light to the alternator in parallel to the charging light so that it comes on when the ignition is switched on and goes out as the engine starts - in short behaves like the perfect oil light.

To check the oil wiring I have in the past taken the oil wire off the oil pressure switch and earthed it against the engine block - if the wiring and bulb are ok it will light the oil light on the dash.

Without checking a wiring diagram, I cannot be certain this is right for a BMW, so check a diagram or ask someone else first since the E34 has an oil level sensor as well. If the suggestion works though you have a faulty engine oil pressure switch which is not closing and earthing the wire when the engine is not running and oil pressure is zero in the engine. You will need a new oil pressure switch. When they fail they tend not to turn the light on at all.

Let us know how you get on and enjoy your 540!

[ben wilamowski]

No I'm fairly certain that the battery light is functioning perfectly correctly.

What baffled me is that when I connected the wire which I believe to be the oil sensor wire to the oil sensor nothing happens to the oil light.

Again when nothing is connected to the oil sensor I get no oil light.

[ben wilamowski]

Hi Simon, thanks for that I haven't tried that yet, I have a new sensor on order but will try just earthing the wire to the block when I get home tonight to see if that brings the light on.

What still baffles me though is that when the wire was connected to the alternator my oil light still refused to light up regardless of ignition switch position!

[simon-york]

I think the alternator indicator tab is 12v positive with the ignition switched on - which means you aren't earthing your oil light, just applying 12v pos at both ends!

Try the earth test, if it works you do need a new sender.

[ben wilamowski]

HI Simon,

I'm really baffled, I did two things last night:

1. Earthed the wire to the block, still no oil light!
2. Performed a binnacle check, ignition off hold down right button on dash turn to ignition two and the binnacle goes through a self check and shows all different functions and lights, except the oil light that is!!!!!

I have a new sensor on order so will hopefully fit that tonight and if that doesn't work I guess I have no option but my local BMW dealer.

Kind regards

Ben

[simon-york]

The oil light is clearly not working at the instrument display end. Swop round the ignition light and oil light and see if the oil light bulb and holder now light up in the ignition position. If they don't then it is likely you need a new bulb/holder combination for the oil light slot.

Keep us all posted!