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      05-15-2010, 12:00 PM   #1
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Oil level sensor malfunction-Need help

I believe the oil level sensor of the engine is malfunctioning. I got the low oil level warning yesterday while driving, and then suddenly it went away. I know the digital readout was full a week ago. The engine cannot have gone through ths much oil in one week of daily commutes. I was not on a hill or any type of incline either.

Again this morning I get the same warning. Is there anyway to determine manually how much oil is in the pan, since we don't have a dipstick? I don't want to be driving the car and damage something.

I had the oil changed just 4,000 miles ago. I have about 28,500 miles on the odometer.
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      05-15-2010, 06:07 PM   #2
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Ask the dealer to replace the sensor.

Mine was DOA the day I picked it up and I had to wait around while they did the work. It wasn't a very good start for my 330xi, but it's been pretty reliable over the last 4 years and 70,000 miles.
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      05-15-2010, 07:09 PM   #3
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The problem is the dealer is not open on the weekends, and until they give me an appointment it could be wednesday of next week...
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      05-15-2010, 07:31 PM   #4
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I had my oil changed a week and a half ago and after only 150 miles, the low oil indicator popped up. Went in today and they put another quart in.

Not sure what caused it (haven't notice oil underneath the car).

I know our cars burn a lot of oil, but 150 miles, really?
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      05-15-2010, 08:37 PM   #5
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This post does not help to fix the oil sensor but rather it explains how the sensor works. The oil level sensor like everything else on a BMW is more sophisticated than it looks, which makes the post too long. Unfortunately, the sensor does not allow to make an easy check of the oil level that the dip stick does.

The oil sensor (OZS) performs two functions - it measures:
(1) oil level, and
(2) oil "quality."
The sensor operates on electrical principle, being designed as a cylindrical capacitor whose capacitance is measured, digitized and processed to yield data that can be converted into parameters (1) and (2).

Oil level: Capacitance depends on the dimensions of the electrodes (diameter and length), and on the properties of the dielectric between the electrodes. The sensor is designed as a capacitor consisting of two coaxial cylinders, made of metal, positioned to be vertical in the engine sump, and acting as electrodes. The oil is admitted into this coaxial arrangement, and since the oil-filled part has a greater capacitance than the part that is free of oil, the level of the engine oil can be determined. The result is displayed to resemble the oil level measured by a dipstick.

Oil "quality:" As capacitance depends not only on the electrodes' dimensions, but also on the properties of the dielectric material (engine oil) between the electrodes, a parameter which can be called oil "quality" can be determined from the capacitance, and fed as one contributing parameter into the algorithm that determines the time for oil change. (It is likely that ideally the oil change algorithm time needs to be reset when the oil has been changed for the algorithm to function "properly.") The "quality" depends on the oil temperature - this is the reason the oil level display is delayed when invoked while the engine is cold.

For those who like math, a formula for the determination of the capacitance is included:
C = [2 pi K(T) L] / [ln(d2/d3)],
where C is the capacitance, d2 and d3 diameters of the electrodes (see cylinders 2 and 3 in diagram), L the oil-filled length of the capacitor, and K(T) is the permittivity (dielectric constant) of the oil, which depends on the oil temperature T; the temperature is measured with a platinum thermometer (item (8) in the enclosed diagram).


A scan of a page from the Bentley's Manual is included, giving a sketch of the sensor that is used in the 3 series, and explaining how the individual parts of the OZS interact. It should be noted that although the OZS sensor looks as one capacitor, it acts as two: the bottom part of the coaxial cylinders is filled with the engine oil and acts as one capacitor, while the upper part of the same two cylinders, being filled with hydrocarbon vapors and air above the oil level, act as the second capacitor. The determination of (1) and (2) from the two capacitances is done by the ECM.
Attached Images
File Type: pdf BMW-OZS sensor.pdf (616.8 KB, 2598 views)

Last edited by Oulixes; 05-15-2010 at 08:45 PM.
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      05-16-2010, 12:24 AM   #6
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Quote:
Originally Posted by nafoo View Post
I had my oil changed a week and a half ago and after only 150 miles, the low oil indicator popped up. Went in today and they put another quart in.

Not sure what caused it (haven't notice oil underneath the car).

I know our cars burn a lot of oil, but 150 miles, really?
Nafoo,

What does your sensor now indicate? Is it back to the max after topping it off?

I am worried about adding a quart and over-filling causing more damage. I doubt the engine burnt so much oil in such a short period.

I hate not being able to do anything until the dealer looks at it! Planning on just stopping by the dealer monday morning without an appointment...
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      05-16-2010, 06:28 AM   #7
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PFitto, a few questions first. Who performed the oil change? Was it a dealer, or independent BMW mechanic, you, or jiffy lube? The reason I ask is are you sure whomever changed the oil knew what they were doing with respect to changing the oil in an E90 and how many quarts they refilled the engine with?

The oil change procedure is very simple, but because the engine doesn't have a dipstick, some mechanics unfamiliar with the E90 can't deal with it and don't add the proper amount of oil. When you change the oil, it all drains out with about 10 ounces or so left in the oil filter housing. The oil in the housing is quite visible when you open the housing and remove the oil filter cartridge. The oil in filter housing needs to be removed also, by either soaking it up with a rag, or sucking it out with a liquid extractor (most auto shops have one). Once the oil is drained and a new filter installed in the filter housing all that is needed is to re-fill the engine with 7 quarts of oil. There is no guessing about the amount of oil to add; it is 7 quarts. Most mechanics are used to a traditional oil change process which is to add 1/2 quart less oil than the engine takes, run the engine for a few minutes, then check the level with the dipstick and add more oil to get the dipstick reading to "full"; which is why, if they are not familiar with the E90, the lack of a dipstick is troublesome to them.

Unless your engine has a major oil leak, which you'd probably notice by now with the smell of burning oil, the engine is not low enough on oil to cause a low oil pressure condition. The car will indicate a low oil pressure condition and make it obvious to shut off the motor, so you needn't worry about damaging the engine under your current situation. The lubrication system in the N52 engine in the E90 is sophisticated because it uses a constant velocity oil pump to maintain a constant oil pressure and flow, as the VANOS/valvetronic system requires unvarying pressure to function properly.

I recommend that if you can't determine how much oil was initially added in the engine at the last oil change, take the car to a BMW mechanic who knows how to change the oil in the dipstick-less E90 and get the oil changed properly. This would be the cheapest way to evaluate the problem. Make sure you ask the mechanic to measure the quantity of the drained oil to help determine if the sensor is reading correctly. Usually the sensor goes bad and doesn't read at all. The sensor is not hard to replace and costs about $160. I’ve checked my drained oil level several times and the sensor has been very accurate in its reading.
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      05-16-2010, 09:38 AM   #8
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Quote:
Originally Posted by nafoo View Post
I had my oil changed a week and a half ago and after only 150 miles, the low oil indicator popped up. Went in today and they put another quart in.

Not sure what caused it (haven't notice oil underneath the car).

I know our cars burn a lot of oil, but 150 miles, really?
?
I haven't used a drop of oil from over a distance of 15,000 mls (according to the gauge)... And that is pretty consistent with the other BMWs I have driven (1997 E39 and 2005 E87 = 4-cylinder, maybe 1/2 quart every 10,000 mls).
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      05-16-2010, 10:34 AM   #9
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^ +1 184,000 miles in my e46 and I never added oil.
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      05-16-2010, 12:51 PM   #10
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Quote:
Originally Posted by ENINTY View Post
PFitto, a few questions first. Who performed the oil change? Was it a dealer, or independent BMW mechanic, you, or jiffy lube? The reason I ask is are you sure whomever changed the oil knew what they were doing with respect to changing the oil in an E90 and how many quarts they refilled the engine with?

The oil change procedure is very simple, but because the engine doesn't have a dipstick, some mechanics unfamiliar with the E90 can't deal with it and don't add the proper amount of oil. When you change the oil, it all drains out with about 10 ounces or so left in the oil filter housing. The oil in the housing is quite visible when you open the housing and remove the oil filter cartridge. The oil in filter housing needs to be removed also, by either soaking it up with a rag, or sucking it out with a liquid extractor (most auto shops have one). Once the oil is drained and a new filter installed in the filter housing all that is needed is to re-fill the engine with 7 quarts of oil. There is no guessing about the amount of oil to add; it is 7 quarts. Most mechanics are used to a traditional oil change process which is to add 1/2 quart less oil than the engine takes, run the engine for a few minutes, then check the level with the dipstick and add more oil to get the dipstick reading to "full"; which is why, if they are not familiar with the E90, the lack of a dipstick is troublesome to them.

Unless your engine has a major oil leak, which you'd probably notice by now with the smell of burning oil, the engine is not low enough on oil to cause a low oil pressure condition. The car will indicate a low oil pressure condition and make it obvious to shut off the motor, so you needn't worry about damaging the engine under your current situation. The lubrication system in the N52 engine in the E90 is sophisticated because it uses a constant velocity oil pump to maintain a constant oil pressure and flow, as the VANOS/valvetronic system requires unvarying pressure to function properly.

I recommend that if you can't determine how much oil was initially added in the engine at the last oil change, take the car to a BMW mechanic who knows how to change the oil in the dipstick-less E90 and get the oil changed properly. This would be the cheapest way to evaluate the problem. Make sure you ask the mechanic to measure the quantity of the drained oil to help determine if the sensor is reading correctly. Usually the sensor goes bad and doesn't read at all. The sensor is not hard to replace and costs about $160. Iíve checked my drained oil level several times and the sensor has been very accurate in its reading.

ENINTY,

I have only had a BMW service center change the oil. Never taken it to Jiffy Lube or done it myself. Also it's the E92 N54 engine....

What I am starting to think is that one of the two dealers (VOB BMW) I have used either didn't actually change the oil, or the sensor is bad.
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      05-17-2010, 10:56 AM   #11
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Quote:
Originally Posted by PFitto View Post
ENINTY,

I have only had a BMW service center change the oil. Never taken it to Jiffy Lube or done it myself. Also it's the E92 N54 engine....

What I am starting to think is that one of the two dealers (VOB BMW) I have used either didn't actually change the oil, or the sensor is bad.
Sorry, didn't see you had a 335i. I think the lubrication system is pretty much the same for the N54. I'd recommend you use Tischer. I've had some work done there and they are pretty good. We bought an E30 at VOB in 1988 and they sold us a damaged car as new. A few years after we bought it I noticed bondo on the door and found pieces of broken window glass in the door when I took the panel off. I'm not a big fan of VOB. Good luck with the issue.
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      06-04-2010, 12:35 PM   #12
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Has anybody had to change the sensor out? How much did it cost? Just wondering...
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      06-05-2010, 04:31 PM   #13
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Quote:
Originally Posted by Mookie469 View Post
Has anybody had to change the sensor out? How much did it cost? Just wondering...
I took mine to the dealer and they finally supposedly drained the oil, measured it and determined it had to be the sensor malfunctioning. They replaced it. I hope they put in new oil instead of the same, but as long as the sensor is new I am fine.

My car is under warranty still, so i was not charged anything.
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      07-04-2010, 10:14 PM   #14
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Just to be clear, would a properly working electronic oil level indicator show intermediate oil levels between the MAX and MIN lines as the oil level goes down from 7 quarts (full) to 6 quarts (1 quart low)? I have never seen an intermediate level during the two years I've owned my E90 N54 (April '08 build date) . Once, it seemed to jump from MAX to MIN just before my first scheduled oil change....hmmm. Do you think my oil level sensor is faulty?

And the service guy at the BMW dealer said that's how they work - either MAX or MIN, but nothig in between(?!?!?!?)...maybe my BMW service guy is faulty too?

Thanks - any insight would be appreciated.
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      07-04-2010, 11:39 PM   #15
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Quote:
Originally Posted by JHR View Post
Just to be clear, would a properly working electronic oil level indicator show intermediate oil levels between the MAX and MIN lines as the oil level goes down from 7 quarts (full) to 6 quarts (1 quart low)? I have never seen an intermediate level during the two years I've owned my E90 N54 (April '08 build date) . Once, it seemed to jump from MAX to MIN just before my first scheduled oil change....hmmm. Do you think my oil level sensor is faulty?

And the service guy at the BMW dealer said that's how they work - either MAX or MIN, but nothig in between(?!?!?!?)...maybe my BMW service guy is faulty too?

Thanks - any insight would be appreciated.
The sensor definitely should display the oil level as it goes down. If it suddenly goes from MAX to MIN then you have a problem. This is not how it works. Just like your cellphone's battery level indicator, our engine oil level indicator should display different measurements as the oil goes down.
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      07-05-2010, 09:41 AM   #16
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I'm heading over to my dealer right now! Thanks for your comments!

UPDATE: The dealer said no error codes were indicated. I also mentioned that I thought the engine was hesitating when cold from stop (I have an AT/paddle shifters). He then said I needed to receive a software update to solve the hesitating issue. The car wsa left overnight at the dealer - it took something like 5 hours, he said, to reload the software. Apparently this solved the hesitating issue (it was NOT the HPFP) and the oil level sensor issue. Dealer said they took out a quart of oil and watched the level sensor go down. They refilled to "Full" so I am diligently watching it to see if it goes down - too soon to tell still.

BTW - car seems much peppier now!

I'm now getting an estimate for the dealer to install H&R coilovers. That'll be done after I get my new wheels...18" VMR v710 with my stock Pilot Sports.

Last edited by Jeffman; 07-10-2010 at 12:15 PM. Reason: UPDATE
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      09-15-2010, 12:05 PM   #17
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^^^ I have been noticing in the past week that it doesnt Calculate (or show the little clock time display) but rather always shows a the oil level.

It is not always the same but even in the morning when the car has been off and sitting overnight I immediatly start the enging and check the oil and it shows full.

Could this be a sign of a faulty sensor?

06 with 58k miles

Thanks guys,
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      02-04-2013, 10:40 PM   #18
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Bumping this old thread because I have a question. Seeing if anyone has experienced this.

I changed my oil this past weekend with 7qts of Motul 300v 10w40. One of the cans was sent "open" w/o the security seal...didn't know until the 2nd can that there was a seal ...I started the car and my oil condition sensor code popped up. I am worried that the oil is bad, 1 can of oil (2 litters) is expired. Motul states 2yr shelf-live, there is no telling how long it's been open.

I have the correct amount of oil in the engine, I did leave the drain plug out awhile, maybe moisture got on the sensor, or maybe sensor is faulty...what are the chances
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      02-24-2014, 08:53 AM   #19
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Quote:
Originally Posted by MrDummy
^^^ I have been noticing in the past week that it doesnt Calculate (or show the little clock time display) but rather always shows a the oil level.

It is not always the same but even in the morning when the car has been off and sitting overnight I immediatly start the enging and check the oil and it shows full.

Could this be a sign of a faulty sensor?

06 with 58k miles

Thanks guys,
I don't know but I just ignore the light now. These stupid German cars have electrical issues and that's a fact. I know when I changed my oil and last time and checked the level etc, I don't have a major leak that I see so it must be the sensor acting weird.
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      03-14-2014, 10:55 AM   #20
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just pulled the code off the cobb and got this taking it to the dealer saturday for an oil change see what they say hopefully nothing major or the sensor is just acting up
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      03-14-2014, 10:58 AM   #21
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Quote:
Originally Posted by Mookie469 View Post
Has anybody had to change the sensor out? How much did it cost? Just wondering...
It's $170 or so online. I plan on doing this with the next oil change since it requires a drain. It's located right next to the drain plug and has one connector and one ground. Easy.
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Last edited by ashmostro; 03-14-2014 at 11:29 AM.
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      03-14-2014, 02:23 PM   #22
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Quote:
Originally Posted by ashmostro View Post
It's $170 or so online. I plan on doing this with the next oil change since it requires a drain. It's located right next to the drain plug and has one connector and one ground. Easy.
I posted a DIY to change out the sensor for the N52 a few months ago, but I'm sure the N54/55 is pretty much the same basic procedure. The sensor is just a big capacitor that uses the oil as the dielectric, there is not much to go wrong with them that would cause it to provide a faulty oil level reading. It's probably the software that interprets the data.
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