I have a stumper. I have a 2001 A4 1.8t AWM engine Avant. While driving the low oil pressure light (red, center cluster) comes on exactly at 1800 RPM after about 2 or more seconds of keeping the RPM at 1800. Never comes on at a higher RPM or lower RPM for any length of time.

Question....why?

The oil pressure was checked by a trusted shop. They connected a mechanical oil pressure gauge and tested the engine according to Audi specs. Cold and hot, various engine speeds, the test results were all good. All within Audi specs.

I've replaced the oil sensor on the oil cooler. I've replaced the oil pick up tube (even though the original didn't really have much stuck in it, not enough to warrant concern). I've tried 15w40 oil with no change in behaviour. Always have used full synthetic. I really don't suspect a mechanical issue with the oil pump or bearing clearance. I've had the exhaust side cam caps off and they look good (the variable valve timing actuator was replaced a few years ago).

I recently replaced the crank case PVC, Suction/Combination valve and relating check valves. No change, oil light still comes on at 1800 RPM. My hypothesis there was maybe something case causing a crank case pressure drop at 1800 RPM thus causing a back pressure on the oil pump lowering the oil pressure momentarily.

I'm getting ready to hook up a mechanical oil pressure gauge and test the car while driving it. So soon I will verify if there is actually a pressure drop. Meanwhile, wondering if any of you have experienced this specific issue?

 

Did you try replacing the oil level/temp sensor on the bottom of the pan?

 

No because it's a oil level sensor and has nothing to do with sensing oil pressure. Do you know if the oil level sensor has ever triggered the low oil pressure light if RPM is at 1800 for longer then 2 seconds? Or has ever triggered it? Isn't there a different dash indicator for oil level?

 

For some reason they all seem to work together. I had an oil pressure issue and that was the last thing I considered (because I was thinking like you), but for some odd reason, that was the fix. They're cheap enough on ebay to give one a shot. Worst case scenario, you have an extra.

G/L

 

My next course of action will be to put a mechanical oil pressure gauge between the oil pressure switch and oil filter housing. I'm going to drive the car until the oil light comes on at 1800 RPM, if there is no oil pressure drop when this happens then I'll try changing the oil level sensor during the next oil change.

The thing that is interesting about this issue is that it comes on exactly at 1800 RPM and it takes a few seconds of the engine at that exact speed before the light comes on. I'm starting to suspect that it's a cluster issue in that it's so precise. I'm going to review the wiring diagram of the oil related sensors. If memory serves me correctly both of those sensors do get wired to the cluster. Maybe it's an internal data processing issue in the cluster. I don't believe it's a wiring issue due to how precise the symptom is.

The car did recently develop a hard start issue (long cranking times). It does eventually start, clears out loaded up cylinders then runs smooth as usual. Could that also be a symptom of a failing oil level sensor on this engine? You have me wondering now.

 

I don't know. It could be a data processing error There's also a tiny chance that it could be the oil pump itself.

It's definitely a head scratcher.

 

Reporting in....I changed the oil level/temp sensor today. Took it for a good test drive, one where I'm sure the light would come on, and it didn't come on. Looks like replacing the oil level/temp sensor resolved the issue.

 

I wonder if the red center oil light in the cluster coming on around 1800 was actually the cluster computer sending a code saying the oil level/temp sensor is out of wack?

 

Glad to hear I was able to help.

G/L

 

Well, I was out driving the car yesterday and the oil light came back on at 1800 RPM. Guess I'm going to have to put a mechanical oil pressure gauge on it and go drive it. I don't understand how this could be an oil pump issue in that the oil light does not come on at any other RPM other then 1800. Or...is it possible the new oil temp/level sensor has already failed?...is there a way to accurately test the oil temp/level sensor? I suspect maybe heating the car up and then testing the sensor?