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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > General E90 Sedan / E91 Wagon / E92 Coupe / E93 Cabrio > Why can't an old ESS be reused after cleaning the oil?



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      10-16-2018, 11:42 PM   #1
greenberet123
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Why can't an old ESS be reused after cleaning the oil?

I just installed a new ESS, but I'm wondering, why can the old sensor not be reused after taking off all the oil? Does a little bit of oil in the terminals on the top really make it stop functioning?

Also, for the new sensor, suppose I have another leak and a little bit of oil gets in the terminals, will it have to be replaced again? Is the sensor so finicky? Asking coz it costs 200 bucks and am worried about having to change it again in case my valve cover starts to leak again.
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      10-17-2018, 09:30 AM   #2
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Good question, subscribed.
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      10-17-2018, 10:33 AM   #3
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Quote:
Originally Posted by greenberet123 View Post
I just installed a new ESS, but I'm wondering, why can the old sensor not be reused after taking off all the oil? Does a little bit of oil in the terminals on the top really make it stop functioning?

Also, for the new sensor, suppose I have another leak and a little bit of oil gets in the terminals, will it have to be replaced again? Is the sensor so finicky? Asking coz it costs 200 bucks and am worried about having to change it again in case my valve cover starts to leak again.
Nobody said you can't reuse it. You could easily clean it up and reuse it, but then it will just leak again. It's not just oil on the top of the terminals. The oil leaks through from underneath the sensor, through the sensor, and comes out the terminals on top, none of which is good for any electronic sensor. If you're going through all the work removing the valve cover to remove the sensor, you might as well replace it with a new one instead of trying to clean it up only to find out that it's still broken.

Leaking valve cover gaskets and leaking eccentric shaft sensors (not the sensor gasket leaking but oil coming through the sensor) are not related issues, though they can seem to happen at the same time on a car with high mileage that has never had either of them replaced. If you just changed it, take a deep breath and relax and don't worry about it. You're good to go for a long time.
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      10-17-2018, 11:53 AM   #4
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Quote:
Originally Posted by lowrydr310 View Post
Nobody said you can't reuse it. You could easily clean it up and reuse it, but then it will just leak again. It's not just oil on the top of the terminals. The oil leaks through from underneath the sensor, through the sensor, and comes out the terminals on top, none of which is good for any electronic sensor. If you're going through all the work removing the valve cover to remove the sensor, you might as well replace it with a new one instead of trying to clean it up only to find out that it's still broken.

Leaking valve cover gaskets and leaking eccentric shaft sensors (not the sensor gasket leaking but oil coming through the sensor) are not related issues, though they can seem to happen at the same time on a car with high mileage that has never had either of them replaced. If you just changed it, take a deep breath and relax and don't worry about it. You're good to go for a long time.
That makes sense, the sensor gets compromised with heat and time and if you see oil on the terminals, the sensor is done.
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      10-17-2018, 12:08 PM   #5
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Quote:
Originally Posted by greenberet123 View Post
I just installed a new ESS, but I'm wondering, why can the old sensor not be reused after taking off all the oil? Does a little bit of oil in the terminals on the top really make it stop functioning?...
My understanding is that when you see oil on the connector or pin-side of the sensor (after removing connector) that is NOT from an external oil leak, such as the sealing gasket on the Valve Cover around the perimeter of the ESS, but rather is from oil getting into the the ESS inside the Valve Cover and leaking THROUGH the ESS, coming out at the pins.

My understanding is that the oil seepage INTO the ESS affects its electronic function in sending the proper variable voltage signal to the DME based upon position of the Eccentric Shaft. So simply wiping oil off the external pins does NOT prevent the internal oil leak from affecting function. That is presumably why you got the three ESS codes you posted in earlier thread.

There have been reported cases on different forums where simply removing the ESS Connector and cleaning the pins was believed to at least temporarily restore adequate ESS function, but given how the BMW Training Manual suggests the ESS functions, I would assume an internal leak into the ESS often occurs with age and thousands of heat cycles, and it is just a matter of time before it develops such an internal leak. Here is a quote from BMW Training Manual, Valvetronic, page 9:
"Eccentric Shaft Sensor
The eccentric shaft sensor (3) signals the position of the shaft back to the ECM. This sensor operates based on the magnetoresistive principle: A ferromagnetic conductor changes its resistance when the applied magnetic field changes its position.

For this purpose, a magnetic wheel (1) that contains a permanent magnet is mounted on the eccentric shaft. As the shaft rotates, the magnetic field lines of the magnet intersect the magnetically conductive material in the sensor. The resulting change in resistance is used as a correcting variable for the signal for the engine control unit."
Due to the safety concerns for proper operation of "throttle by wire" I believe I read somewhere that there are actually TWO sensors or signals and that a Fault is saved and warning displayed, perhaps even limp mode, if the sum-total of the signals does NOT equal a certain value, or if the two signals are NOT otherwise consistent. Given that the Sensor Connector has 8 active pins, that would suggest such a dual sensor. The Accelerator Pedal Module has two sensors for that reason.

So I would assume that the common failure mode results in a Fault Code for implausible signals when comparing the two. I can't find anything specific at the moment that confirms my recollection, so if ANYONE can site a reference that addresses that issue, please advise.

George
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      10-17-2018, 04:15 PM   #6
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Thanks everyone! These are amazing detailed responses! If the oil is seeping in through the ESS, it totally makes sense to replace the whole unit.

I had always assumed that the oil was leaking from the ESS seal and then entering the terminals, didn't realize that the entire sensor was compromised with oil. This makes me much more satisfied about changing the ESS.
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      10-17-2018, 05:01 PM   #7
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In some cases you might be right. If there was only
a way to test it on the bench once clean.
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      10-17-2018, 05:11 PM   #8
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Quote:
Originally Posted by gbalthrop View Post
My understanding is that when you see oil on the connector or pin-side of the sensor (after removing connector) that is NOT from an external oil leak, such as the sealing gasket on the Valve Cover around the perimeter of the ESS, but rather is from oil getting into the the ESS inside the Valve Cover and leaking THROUGH the ESS, coming out at the pins.

My understanding is that the oil seepage INTO the ESS affects its electronic function in sending the proper variable voltage signal to the DME based upon position of the Eccentric Shaft. So simply wiping oil off the external pins does NOT prevent the internal oil leak from affecting function. That is presumably why you got the three ESS codes you posted in earlier thread.

There have been reported cases on different forums where simply removing the ESS Connector and cleaning the pins was believed to at least temporarily restore adequate ESS function, but given how the BMW Training Manual suggests the ESS functions, I would assume an internal leak into the ESS often occurs with age and thousands of heat cycles, and it is just a matter of time before it develops such an internal leak. Here is a quote from BMW Training Manual, Valvetronic, page 9:
"Eccentric Shaft Sensor
The eccentric shaft sensor (3) signals the position of the shaft back to the ECM. This sensor operates based on the magnetoresistive principle: A ferromagnetic conductor changes its resistance when the applied magnetic field changes its position.

For this purpose, a magnetic wheel (1) that contains a permanent magnet is mounted on the eccentric shaft. As the shaft rotates, the magnetic field lines of the magnet intersect the magnetically conductive material in the sensor. The resulting change in resistance is used as a correcting variable for the signal for the engine control unit."
Due to the safety concerns for proper operation of "throttle by wire" I believe I read somewhere that there are actually TWO sensors or signals and that a Fault is saved and warning displayed, perhaps even limp mode, if the sum-total of the signals does NOT equal a certain value, or if the two signals are NOT otherwise consistent. Given that the Sensor Connector has 8 active pins, that would suggest such a dual sensor. The Accelerator Pedal Module has two sensors for that reason.

So I would assume that the common failure mode results in a Fault Code for implausible signals when comparing the two. I can't find anything specific at the moment that confirms my recollection, so if ANYONE can site a reference that addresses that issue, please advise.

George
Some good knowledge here.
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