Oil Level Sensor Issue

Hi all,
I'm having an issue with my 2011 M3 oil level sensor that neither I nor my local BMW independent shop can figure out. It's been going on for about the last 10,000 miles, and I'm hoping someone here might be able to help.

When the car is stationary, the oil level reads normal. But after 10–15 minutes (sometimes less) on the highway, the oil level drops to "below minimum add a quart." The oil warning light comes on, and the cluster and head unit both show the same "below minimum" message.

Here’s how it typically happens: I leave my house for work, and roughly 5–15 minutes into the drive — once the oil temperature and driving conditions are met to allow automatic measurement — the reading shows "below minimum" and the oil light comes on. Then, once I arrive at work and let the car idle in a parking spot, I manually check the oil level and it goes back to full. This happens like clockwork, every time I drive the car.

Even if I let the car reach operating temperature in the driveway and measure the level before heading out, it still goes from full to below minimum once I’m out on the road. Around-town driving triggers it too, but it usually takes longer or might just read "minimum — add 1/2 quart."

Since I couldn’t figure it out myself, I brought it to a reputable independent BMW shop here in central Jersey. They had the car for two weeks and tried several things:

Replaced the oil level sensor (twice)

Reprogrammed the ECU, cluster, and head unit

Possibly checked the wiring harness (not entirely sure, but I think they did)

Checked some of the communication lines, including IBS and CAN

There were a lot of phone calls between the shop and me during this time, so I may be forgetting a few things.

In the end, they couldn’t identify the root cause. They told me they could probably figure it out eventually, but that the additional diagnostic time and potential parts/labor costs may not be worth it, especially with no guarantee of a solution. At this point, they’d be throwing parts at it to see what happens.

I’ve done a lot of searching online and only found a few threads describing this exact issue. Most don’t have any working solutions, and the few that do haven’t worked for me.

Short of taking it to the dealer or blindly replacing more parts, I’m out of ideas. I'm at the end of the rope on this one. Any help or insight would be greatly appreciated. Thanks in advance.

edit: I also forgot to mention something important. Taking off the oil filler cap and looking down into the engine, I noticed one of the plastic vanos caps broke apart. I even see a piece of the plastic wedged in there (not touching any moving parts). not sure how much of it broke off, but I assume the whole piece is gone. I believe I've heard some horror stories, what it can do to these engines. I think it happened a while ago and engine seems to run fine. I figure my next step is getting that vanos cover off and get them replaced. Possible this can impact the sensor/oil flow? I assume the plastic would have been picked up by the oil filter and removed from oil changes, but there might be some bigger pieces still in there.

What year, model and engine are we talking about?

2011 M3 s65 engine

I read there that you checked comm but have you physically toned out your wires with a meter? Unplug the wire at the sensor and unplug it at the DME (under passenger side windshield). Maybe one of the wires is partially cut? I would test each conductor and wiggle the fuck out of the oil sensor connector while doing so. Maybe one of the wires developes resistance once things get warm?

I believe the wiring harness was checked by the shop, but good idea to do that again myself.

I also forgot to mention something important. Taking off the oil filler cap and looking down into the engine, I noticed one of the plastic vanos caps broke apart. I even see a piece of the plastic wedged in there (not touching any moving parts). not sure how much of it broke off, but I assume the whole piece is gone. I believe I've heard some horror stories, what it can do to these engines. I think it happened a while ago and engine seems to run fine. I figure my next step is getting that vanos cover off and get them replaced. Possible this can impact the sensor/oil flow? I assume the plastic would have been picked up by the oil filter and removed from oil changes, but there might be some bigger pieces still in there.

Do you add oil as the car instructs to then be told it is overfilled when stationary?

spazzyfry123 wrote

Do you add oil as the car instructs to then be told it is overfilled when stationary?

Yeah, I already tried that. Started with the oil level full when stationary and with it going below minimum on the highway. Then added oil in small increments past full hoping the level would be higher on the highway. Got to the point where it read overfilled stationary and still below minimum on the highway. Rarely it will read low add 1/2 quart, but usually in the same drive it will go lower and say below minimum add 1qt.

BTW, replaced vanos caps and oil separators over the weekend. Read a post that replacing the oil separators helped. Thought bad oil separators messing with crankcase pressure may lead to bad oil readings, but still no change.

It’s been a while since I last looked into this issue, but I’ve come up with a new theory. It’s probably not something I’d spend the time or money on right now since dropping the oil pan requires dropping the front subframe, but it would be cool to hear opinions on whether this theory makes sense or is even worth investigating.

(Please correct me if anything here is incorrect)
From what I understand, the S65 engine uses two oil pumps — a main pressure pump and a scavenger (or return) pump. The oil pan is divided into two sections: the front portion holds about 1.5 liters of oil, while the main rear section holds the rest. The scavenger pump is located in the front section, and its job is to return oil from the front sump back to the main rear sump, where the primary pump draws from.

Here’s my thought: when one of the plastic VANOS caps broke apart (they’re located near the front of the engine), some pieces may have fallen down behind the timing chain covers into the front section of the oil pan. Those fragments could be partially blocking the scavenger pump’s pickup or internal passages — hopefully stopped by the pickup tube screen, if there is one.

At idle or low RPM, the restriction might not matter much, allowing oil to return to the main section at a sufficient rate. But at higher RPM, the main pump could be circulating oil through the engine faster than the scavenger pump can return it. If that happens, oil would temporarily accumulate in the front section of the pan. Once the front compartment (roughly 1.5 L) fills up, it likely overflows back into the main section since the two areas aren’t completely sealed from one another.

This would explain why the engine doesn’t starve for oil, 1.5L out of a 9.3L total capacity isn’t enough to go too low and lose pressure — but it would be enough to trigger a low oil level warning. It also makes sense because the oil level sensor is located in the main section of the pan, so it would detect the temporary drop in oil volume there when the front scavenger can’t keep up.

It’s been at least 15,000 miles since this issue first started, and the engine still runs great. So I’m not really concerned about any damage — it’s just annoying having the low oil level light come on every time I get on the road.

Some may think I'm overthinking this issue, and it's just wiring or sensor issue or something like that. But my thought is it's been looked over pretty thoroughly by an Indy, though not to the extent of tearing into the engine or checking the pumps directly.

Thanks in advance for any input or thoughts on this.