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General E46 Forum
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Old 03-18-2017, 07:29 PM   #21
helkenndg
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Sensor light failed me...04' 325CI

Fellow E46ers,

I have a slightly different issue than every other post I have read. My issue is that the light failed me.... Here is the background, my daily driver is a 04' 325CI she has been a dream since the day she came home with me in late 2010. 196k miles later she is still running smooth, strong, and responsive just as the first day I drove her. By the book maintenance, regular oil and filter changes and replacing typical wear goods are the reasons she has been so nice to me. I broke the "by the book maintenance" rule 18 months ago when I learned she had a rear main seal leak that would cost over $1000 to get fixed. Since I had my 08' 335i convertible, my 14' Audi S5, and my very low mileage 93' 300zx Convertible as other available cars (albeit prefer not to use as a daily driver) my solution was to utilize BMW's oil sensor to alert me when I needed to add Mobil One Synthetic 5W-30 oil.

The thought was to look for the yellow oil light when I shut the car off, this in turn would trigger me to check the oil and typically add 1/2 to 3/4 of quart. This process has worked perfectly for the last 18 months...UNTIL recently

I had my scheduled oil change just as I always do, and drove my girl like I always do. Truthfully I looked for my trusty yellow light to tell me she needs to have 1/2 to 3/4 of one quart added. No light!! Typically I could get about 700 to 800 miles before she would issue the yellow light. Once I hit 2800 miles I realized that the rear main seal did not fix itself, so when I checked the dip stick, yup you guessed it the oil level was way down. So not shocking actually if you do the math (700 to 800 miles = 1/2 to 3/4 quart divided by 2800 miles = 2-1/4 to 3 quarts low.

The only wet spot on the dip stick was the very tip....did I mention NO LIGHT, yellow or red, running or not. So to get the oil in between the dip stick notches, I added 2-3/4 quarts (was not exactly 3 quarts, but used 3 quarts for math purposes). Proceeded to immediately drive her 250 miles that day (125 miles outbound) checked oil, it was perfect, (125 miles inbound) checked the oil, it was perfect. She is running smooth and strong just like she always has. No lights, no codes, no performance issues, no overt issues at all.

Everyone is talking about the oil sensor and what to do when it comes on "yellow or red", well what would make it not come on? Now before you say check the bulb, when you turn on the key the cluster lights up all of the warning lights to insure the bulbs are functional, both the yellow and red oil light bulbs ARE operational. So some where between the sensor and the light in the cluster is not working.

Sorry for the length of this, but my questions are simply: 1) Did I do any damage... 2) Any suggestions as to why my trusty oil sensor light did not come on at all (yellow or red)?

Thanks
Dave

Last edited by helkenndg; 03-18-2017 at 08:08 PM.
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Old 03-18-2017, 07:47 PM   #22
jdstrickland
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NOT come on? It should come on when the key is in Position II (RUN), before engine start. If yes, then you have something wrong with the low oil sensing circuit. It no, then the light is out.
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Old 03-18-2017, 08:13 PM   #23
helkenndg
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It comes on when you turn the key,(cycles through all warning lights), so the light works.... But the light is not getting a low oil signal from the sensor, so either the sensor is bad or dirty, or there is an issue with the wiring harness. Has anyone ever heard of this or had this issue?
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Old 03-18-2017, 08:50 PM   #24
hitbyastick
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You should maintain your car. Relying on an idiot light whilst polluting the environment is laziness and false economy.
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Old 03-18-2017, 09:04 PM   #25
helkenndg
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hitbyastick, not only is that not helpful, but ignorant and makes no sense. Maybe a forum whereby the discussion is centered around the environment would be a better spot for your opinions! This forum is focused on the BMW e46.
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Old 03-19-2017, 01:38 AM   #26
juslookin
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Replace the sensor. Hella is OE brand.


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Old 03-19-2017, 06:55 AM   #27
helkenndg
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Thanks Justlooking & JD, I will change the sensor and see if that works. Still hoping that someone out here has experienced this issue and what they did.
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Old 03-20-2017, 12:08 PM   #28
jdstrickland
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The typical failure mode for the Low Oil Sensor is to report low oil when the level is actually good. The symptom is that the oil light will cycle correctly as the key is turned to start the car, then after engine start the light goes out for a few seconds, then comes on again as the engine is running, then eventually -- 20-ish seconds or so -- goes out again and remains out until a subsequent engine start.

The Low Oil Sensor is a comfort feature for the vehicle operator. It is intended to keep the operator from having to open the hood and physically check the normal and customary stuff that vehicle operators should routinely monitor. There are sensors to monitor oil level, brake fluid level, coolant level, and wiper fluid level. These are critical safety of flight items that need to be monitored, BMW hopes that the sensors reliably monitor and report these items. Having said that, even BMW says that one should make a habit of lifting the hood to look at these things, in addition to the condition of the belts and hoses.

I am not aware of a low oil sensor failing to report the oil level when the level is low. There are ample comments of the sensor falsely reporting low oil when the level is okay.
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Old 03-20-2017, 12:30 PM   #29
jdstrickland
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FOR THE RECORD
The Low Oil Sensor does not have the granularity to detect a 1/2 to 3/4 quart of low oil. Indeed, this amount of low is of absolutely no consequence to the proper operation of the engine. Low oil is something greater than a full quart/liter (depending upon your market). The oil dip stick has a High and Low mark. The level is perfectly acceptable at any point between those two marks. Low is where you add a full quart/liter to bring the level up to the High (Max.) mark. There is never any reason to go through the effort to add less than a quart/liter, therefore there is no reason for the Low Oil Sensor to have this degree granularity. Having low oil of less than 1 quart/liter is not the cause of the problem, whatever the problem is.

Proper checking of the dip stick is to pull the stick and wipe it. Ignore anything you observe relative to the level, although looking for signs of water/coolant is certainly reasonable. Re-insert the dipstick then pull it out, NOW you can get a reading of the oil level. It is typical that if the oil is at the very tip of the stick, then you are 2 quarts low. If off the end of the stick then more than 2 quarts low. Add oil until the level is anywhere between the two marks that indicate the Min and Max levels.

Your engine holds 7 quarts, 8 quarts if you have the xi, of engine oil. My humble opinion is that you did no damage, and if you had not caught this when you did you would have seen the low oil indication soon anyway. I don't know what the rate of loss is, but the BMW rear main seal is pretty robust and has not been the focus of service activities on any routine basis. That is, it's not a common failure point of the M50/M52/M54 engines. A far more common failure item is the valve cover gasket that leaks oil down the rear of the engine mostly due to the engine being raised in the front so the oil pools in the back as it drains back to the oil pan to be sucked up by the oil pump to begin the cycle again.

You could drive like you are in a Fast and Furious movie, and then you might be concerned that you are 2 quarts low. But if all you do is ply the highways and byways from your house to your office and don't get crazy doing so, then being 2 quarts low is within the operational parameters. You will see high oil temps, perhaps. But there is more than enough oil to keep the pick-up for the oil pump submerged so that the pump can collect enough oil to lubricate the vital engine components. Bad practice? Sure. Fatal? No.
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Old 03-20-2017, 08:33 PM   #30
helkenndg
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Thanks for the very helpful info JD. There is never any oil on the ground, I think I will just bite the bullet and have the dealer fix the rear main seal...
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Old 03-21-2017, 06:29 AM   #31
juslookin
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Oil level is fine but Oil Sensor light comes on anyway

Is the RMS leaking? The oil pan gasket runs to the transmission and can look like a RMS leak.

Shouldnt start changing parts if you dont know for sure. That will turn into a hefty bill if you dont DIY.

The oil pan gasket sits under the RMS and on older brittle gaskets dropping the transmission can break part of the gasket and cause a leak.

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Last edited by juslookin; 03-21-2017 at 06:33 AM.
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Old 03-21-2017, 09:45 AM   #32
s3bas
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Sound like oil level sensor , very inexpensive diy

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Old 06-07-2017, 10:57 AM   #33
kd7iwp
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Quote:
Originally Posted by jdstrickland View Post
The typical failure mode for the Low Oil Sensor is to report low oil when the level is actually good. The symptom is that the oil light will cycle correctly as the key is turned to start the car, then after engine start the light goes out for a few seconds, then comes on again as the engine is running, then eventually -- 20-ish seconds or so -- goes out again and remains out until a subsequent engine start.
This is the problem I'm currently experiencing exactly, so I'll replace this sensor soon and see if the light goes away.
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Old 06-07-2017, 03:25 PM   #34
helkenndg
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Update...brought it to the dealer they determined is was NOT the rear main seal but rather a tiny leak at the front of the oil pan and the occasion drip only happened when driving, thus it was caught by the plastic undercover and never ever left any puddles when parked. In addition as everyone said the oil sensor was also bad. Had a new gasket installed on the oil pan amd a new sensor, $600 later no issues. Thanks to juslookin, his diagnosis was spot on.

Last edited by helkenndg; 06-07-2017 at 03:29 PM.
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Old 06-07-2017, 03:28 PM   #35
helkenndg
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juslookin was spot on

Quote:
Originally Posted by juslookin View Post
Is the RMS leaking? The oil pan gasket runs to the transmission and can look like a RMS leak.

Shouldnt start changing parts if you dont know for sure. That will turn into a hefty bill if you dont DIY.

The oil pan gasket sits under the RMS and on older brittle gaskets dropping the transmission can break part of the gasket and cause a leak.

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Juslookin you were spot on... Not RMS and it was the oil pan and sensor. Juslookin knows his stuff...Thanks
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