Faulty Oil Pressure Warning??

[Alas]

Got an odd fault on a 1999 A6 TDi 1.9:
Turn on ignition, dashboard goes through self check including illuminating the oil warning light (so the bulb works), OK so far....
I can't get the oil warning light to come back on, even when it should,eg stall the engine or disconnect the pressure switch..!!!!!

Checked the pressure switch (single wire type), shows open circuit (to earth) when engine not running, and short circuit (to earth) when the engine is running. So the switch is OK.

Checked the wire to the switch; disconnected from the switch shows battery voltage with engine running (still no warning lamp on dash), so the wire is connected to something at the other end (so not a broken wire).

Anyone seen this problem before??

(Would be nice to know if I loose oil pressure..!!!)

[karlaane]

There are two sensors.

[Crasher]

It doesn’t work like that, it is a dynamic system. If you disable the engine and crank it over for a prolonged period (such as after changing a fuel filter) the warning will come on.

[Alas]

Hi, thanks for the replies.
Karlaane, Where is the other sender?
Crasher, If you are cranking the engine the oil pump will turn, and should (unless worn, or worn crank bearings) provide enough pressure to keep the low pressure light off.
I had the engine running and disconnected the wire from the switch, still no warning light?

[Crasher]

Not enough pressure under cranking, the crank speed is too slow. Often on here we have people whose cars won’t start for one reason or another and they often add that the oil pressure warning went off under prolonged cranking, which is normal.

[Alas]

So is the only way of testing the oil presure low warning circuit by cutting off the diesel supply, and cranking the engine for a long period?
There must be a test that is a little easier on the bearings/starter motor?

[paul b]

Not sure if this is quite what you mean...

But on all 3 of my VAG TDIs, when I turn the ignition on the oil light illuminates very briefly and then goes out regardless of whether I start the engine or not. Even after stalling, the oil light will not illuminate.

I believe it to be normal.

[Crasher]

Using VAG-COM or similar, Measuring Blocks 08, Display Group 001 Display Zone 3 shows oil pressure switch 2 status, with a registered version of VAG-COM, visual and audible warnings can be triggered in Output Tests 03. There is no Audi method of testing the light I know of, just the switch and the pressure itself. The switch should close its contact at 0.75 to 1.05 bar.

[Alas]

Thanks Crasher, I will give that a go.

[karlaane]

Hi, thanks for the replies.
Karlaane, Where is the other sender?
Crasher, If you are cranking the engine the oil pump will turn, and should (unless worn, or worn crank bearings) provide enough pressure to keep the low pressure light off.
I had the engine running and disconnected the wire from the switch, still no warning light?

I am not quite sure on 1.9, but on a 2.5 there are two sensors, both sensors are on the left side of engine block below and slightly behind the thermostat housing. One is large and has two plugs, it is the oilmanometer and oil lamp, the other is for the oil lamp. One works at low rpm, the other high.

K