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740 Posts
Discussion Starter · #1 ·
So two weeks ago did an oil service on my E46. Also replaced the sump sensor as I was getting the yellow light after startup. Two or three days after the service I was on my first long drive and yellow light stayed on after I switched biggie as I figured it was a bit short...checked the dipstick and oil was at half way mark..added another bit to bring it to within a 2-3mm of top and all was well for a week...yesterday go the damned yellow light again after startup and its happening all the time now.

Soooo... is it posible that the connectors are causing the issue. ?
Where abouts is the second oil sensor (I think there is one) ?
CAn that few mm from top really make the difference

I had thought about the operation of these units. IF the are really thermistors then how come you get a light on startup. Surely rate of heating up has more to do with how fast its leaving the sump rather than how much is there...As the oil drains back in after shutdown how come it "knows" so quickly I have a low oil level. It cant have drained back that fast.

Any thoughts please..this is really buggin me..
Some additional information I also gathered may be useful to the more technical minded of you.

So I have three located normally in the sump which may or may not be faulty. The old (original) sensor that I replaced at the last oil change and a new sensor that the parts supplier sent to me when I contacted them to say I thought the OEM replacement one might be faulty...

I plugged in these in turn to the sensor socket and examined the behaviour of the yellow oil light...heres what I found.
I'l call these sensor 1 (current sensor in sump)
2 (old original sensor that I assumed was faulty)
3 (New replacement sensor)
for convenience

1) Current situation is that with the sensor 1 plugged in I get a yellow light 10-12s after starting the car which stays on for 15s approx and does not come back on after ignition off

2) With sensor 1 in place but the electrical connection disconnected I get the same behaviour as above

3) With sensor 2 plugged into the electrical socket I get a yellow light that stays on permanately and also stays on after engine is shut off.

4) With sensor 3 plugged into the electrical socket I get no yellow lights at all.

Now here are my conclusions

Just looking at 1 and 2 together suggests that the fault is in the electrical circuit since I'm getting the same behaviour with or without the sensor plugged in.

Observation 2 is to be expected since the sensor does not see any oil and indicates its is dangerously low by illuminating and staying on after ingition shut off. However this also suggests that the sensor I replaced is actually working fine.

Observation 3 is strange since I would have expected to see the same observation as in 2 due to the sensor not seeing any oil at all.

Finally I measured the resistance (since this unit is essentially a thermistor) between the terminals on sensor 2 and 3. Here are the results

Sensor 2
1-2 1.05 MegaOhm
1-3 1.4 MegaOhm
2-3 1.1 Megaohm

Sensor 3
1-2 0.95 MegaOhm
1-3 1.4 MegaOhm
2-3 1.1 MegaOhm

This essentially indicates to me anyway that both these sensors are identical but I still get different behaviour when plugged into the socket.

I should menion that I cleaned the terminals of the socket as best I could before starting this test.

Apologies for the mammoth post


740 Posts
Discussion Starter · #3 ·
No its from a specialised BMW suppliers in wolverhampton. They've sold loads and not had problems and I also compared it visually with the one my indy uses in his garge and its the same.
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