# Faulty NOX and oxygen sensors



## Runnerman2 (Jan 26, 2011)

On our 2010 335d, which now has 60,000 miles on it, we have recently had to replace two faulty sensors. One was an NOX sensor and the other was an oxygen sensor. Total cost for the two, which failed at 56,000 and 58,000 miles, was $1,300. Now the SES light is back on, and the dealer says the heater for the DEF tank (reserve) is staying on constantly, probably due to another faulty sensor! Estimate is around $700 to replace. 

Here's the deal---we love this car and would love to keep it a long time. But these faulty sensors are getting to be a huge expense, not to mention the downtime in the shop these replacements entail. 

Any hope for our car? What could be causing these ongoing issues? Any advice would be greatly appreciated.


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## Penguin (Aug 31, 2003)

Now you know why some people say BMW stands for Break My Wallet.

Unfortunately, NOx sensors seem to be a not uncommon problem, and it's not limited to BMWs. In talking with some Over The Road semi drivers, it seems the NOx sensors are also turning-out to be a problem on the newer OTR diesels as well (This is just anecdotal information, as I have no quantitative data). 

My NOx sensors were replaced at around 37,000 miles.

So I would say that you are simply experiencing the "luck of the draw" and that there is likely no specific cause you can address to prevent future issues, e.g., diesel SCR technology is relatively new and it's just the nature of the beast.

But if you are the original owner, I would press the dealer for some "good will" assistance from BMW NA, particularly since you have already forked-out bucks for the Sensor problem If the dealer goes to bat for you, they often can get BMW NA to pony-up for part of the repair cost, either through splitting the repair cost or offering free parts with you paying the labor. Of course, the dealer can't do this for everyone, so you have to give them a reason to go to bat for you in preference to other customers, e.g., getting or not getting some assistance might impact your buying you next vehicle from them, or being such a nice guy that they want to help you. Different approaches work with different people, so you're on your own as to how to convince them they should try to help you get help from BMW NA.


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## Pierre Louis (Oct 23, 2011)

The high pricing of these services may reflect the use of a dealer instead of an independent BMW specialist. Has anyone priced these parts from a different source?


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## Flyingman (Sep 13, 2009)

Runnerman2 said:


> On our 2010 335d, which now has 60,000 miles on it, we have recently had to replace two faulty sensors. One was an NOX sensor and the other was an oxygen sensor. Total cost for the two, which failed at 56,000 and 58,000 miles, was $1,300. Now the SES light is back on, and the dealer says the heater for the DEF tank (reserve) is staying on constantly, probably due to another faulty sensor! Estimate is around $700 to replace.
> 
> Here's the deal---we love this car and would love to keep it a long time. But these faulty sensors are getting to be a huge expense, not to mention the downtime in the shop these replacements entail.
> 
> Any hope for our car? What could be causing these ongoing issues? Any advice would be greatly appreciated.


Runnerman, what happened with the extended warranty? I think for these cars and piece of mind, and to not lose a piece of your...well wallet, it is a must.

Is it still an option for you to get? Perhaps through an alternative source other than BMW?

The emissions crap on these cars are rediculously expensive and frequently failing.

I had my DEF heater go out and it required a complete new transfer pump assembly. That was at 50k miles and under warranty. I live in Florida so if it were my own nickel I doubt I would have fixed it.


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## tonyspumoni (May 23, 2010)

I have had both of mine go out as well on a 2010 335d, the O2 sensor at about 30k and the NOS at 55k. Not uncommon at all I fear. Both covered under the CA emissions warranty, which is 70k/7 years and exists outside of other warranty coverage. It sure would be nice to know more or less how frequently this has occurred to others. 


Sent from BimmerApp mobile app


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## Pierre Louis (Oct 23, 2011)

tonyspumoni said:


> I have had both of mine go out as well on a 2010 335d, the O2 sensor at about 30k and the NOS at 55k. Not uncommon at all I fear. Both covered under the CA emissions warranty, which is 70k/7 years and exists outside of other warranty coverage. It sure would be nice to know more or less how frequently this has occurred to others.
> 
> Sent from BimmerApp mobile app


I had both NOx sensors replaced at around 32,000 miles along with both catalytic converters. This may have been from an overload of "gunk" caused by a change in driving - I used to downshift heavily to clear the soot in my older CR diesels which would cause one plume of black smoke, and now I started again and likely overloaded the converters, I don't know.

Cost of parts at BMW Parts Giant:

SENSOR Upper; Top

MSRP/Core ?/Save/Online Price
$274.18/$0.00/$78.14/$196.04

EMISSION SYSTEM / EMISSION SYSTEM / DIESEL AFTERTREATMENT SYSTEM / SENSOR
SENSOR Upper; Bottom

MSRP/Core ?/Save/Online Price
$77.48/$0.00/$17.04/$60.44

EMISSION SYSTEM / EMISSION SYSTEM / DIESEL AFTERTREATMENT SYSTEM / SENSOR
SENSOR Lower

MSRP/Core ?/Save/Online Price
$77.48/$0.00/$17.04/$60.44

EXHAUST SYSTEM / EXHAUST SYSTEM / EXHAUST SYSTEM / CATALYTIC CONVERTER

CATALYTIC CONVERTER 3 Series; Rear; Cylinders 1-3; w/Turbo

MSRP/Core ?/Save/Online Price
$1,375.51/$50.00/$392.02/$983.49

CATALYTIC CONVERTER 3 Series; Rear; Cylinders 4-6; w/Turbo

MSRP/Core ?/Save/Online Price
$1,375.51/$50.00/$392.02/$983.49

My experience with dealers is that occasionally, some don't follow MSRP, going higher or lower, but usually you pay the MSRP at the dealer and the private mechanic may charge less.


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## Hoooper (Jun 17, 2013)

without a diagram, those prices dont mean a lot. Not sure what they really are. Part numbers off of RealOEM point to $400 sensors (from bmwmercedesparts.com) for the primary NOx sensor and the after catalytic converter NOx sensor. Based on the prices and diagrams given from realOEM, your $196 part is the oxygen sensor and the other parts are probably pressure sensors for the DPF

http://www.realoem.com/bmw/showparts.do?model=PN73&mospid=51054&btnr=13_1288&hg=13&fg=15

http://www.realoem.com/bmw/showparts.do?model=PN73&mospid=51054&btnr=13_1287&hg=13&fg=15


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## Runnerman2 (Jan 26, 2011)

From all the posts, y'all have convinced me that we're in for more expense with these sensors. This latest one is for the smaller DEF resevoir. According to the technician, the sensor is reading a temp of -6 degrees----that would be an all time record low here in our part of the great state of Texas! That's why the DEF fluid heater is staying on all the time. I guess when it finally burns out, another sensor will light up and report that, too. We did not opt for the extended warranty (in hindsight.....); we DO use a very good independent shop whom we trust, and these sensors are not covered in Texas past the 50,000 factory warranty, as they are in CA. At any rate, thanks for the information, and we'll keep our fingers crossed that we won't have much more of this in the future.


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## F32Fleet (Jul 14, 2010)

Runnerman2 said:


> From all the posts, y'all have convinced me that we're in for more expense with these sensors. This latest one is for the smaller DEF resevoir. According to the technician, the sensor is reading a temp of -6 degrees----that would be an all time record low here in our part of the great state of Texas! That's why the DEF fluid heater is staying on all the time. I guess when it finally burns out, another sensor will light up and report that, too. We did not opt for the extended warranty (in hindsight.....); we DO use a very good independent shop whom we trust, and these sensors are not covered in Texas past the 50,000 factory warranty, as they are in CA. At any rate, thanks for the information, and we'll keep our fingers crossed that we won't have much more of this in the future.


Ya. I think the sensor is integrated in the tank.


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