Looking for a bit of advice. My 2012 BMW 1 series Msport (72000 miles) just failed its MOT on emissions as the lambda was too high. The garage said they ran diagnostic and the NOX sensor needs replacing. This is quite an expensive job (£620 including parts, labour, VAT ect). I’ve said I’ll have a think and took the car home and ran my own OBD diagnostic tool on the car. My concern is no error codes have come up. I took the car to another garage for an emissions test and they did confirm the lambda is too high to pass MOT.

My question is, is it possible for the NOX sensor to be causing the emissions test to fail when it is not showing up as an error on my diagnostic tool?

Hi Kenny. 
what scanner do you have?

a generic ‘cheap scanner’ will not pick up every code I have found in my experience. 
a garages equipment is much more advanced. 
my mates mini failed in emissions badly and was told the whole cat, exhaust and sensors needed replacing… a full tank of premium fuel and a couple of bottles of redex, followed by an hours run before the MOT sorted everything 😀

how handy are you with spanners?  I wouldn’t have thought it would be that difficult to replace. 

Morning Kenny

It depends on what diagnostic reader you have as to whether you see a fault or not. How ever most peoples first warning is the EML, check the intake side for any air/vacuum leaks but as you seem to have 2 confirmations it seems you may have failing Lambda's

Take a look at www.realoem.com put the last 7 digits of your Vin into the search box it will call up your model, then check the exhaust section to get the part number. Once you have the part number Google it to find the best price. remember BMW don't make sensors they buy them in so most Auto Factors can supply them. Actually changing them is a fairly straight forward process just take your time (youtube videos will help) one on top and one underneath. Cost I would guess at £50 for the top £100 for the long one underneath

Dave

9 hours ago, X5smw said:

Hi Kenny. 
what scanner do you have?

a generic ‘cheap scanner’ will not pick up every code I have found in my experience. 
a garages equipment is much more advanced. 
my mates mini failed in emissions badly and was told the whole cat, exhaust and sensors needed replacing… a full tank of premium fuel and a couple of bottles of redex, followed by an hours run before the MOT sorted everything 😀

how handy are you with spanners?  I wouldn’t have thought it would be that difficult to replace. 

yeah it is a generic cheap scanner to be honest. O wow I really hope that doesn’t happen to me haha! 
 

Not great with spanners. That does make me feel better though knowing it could be the issue though. Just wanted to make sure the mechanic isn’t taking me to the cleaners getting work I don’t need.

 

appreciate the help.

9 hours ago, Greydog said:

Morning Kenny

It depends on what diagnostic reader you have as to whether you see a fault or not. How ever most peoples first warning is the EML, check the intake side for any air/vacuum leaks but as you seem to have 2 confirmations it seems you may have failing Lambda's

Take a look at www.realoem.com put the last 7 digits of your Vin into the search box it will call up your model, then check the exhaust section to get the part number. Once you have the part number Google it to find the best price. remember BMW don't make sensors they buy them in so most Auto Factors can supply them. Actually changing them is a fairly straight forward process just take your time (youtube videos will help) one on top and one underneath. Cost I would guess at £50 for the top £100 for the long one underneath

Dave

Hi Dave,

 

It is a cheap one tbh, though it did successfully identify a faulty sensor elsewhere in the past. I’ve had no EML come up and not noticed any issues with performance, which is why was a bit suspicious of the mechanic, as NOX sensors are so expensive (though as you say definitely something wrong with lambda reading)

 

perfect thanks for the recommendation, I’ll have a look at that site. I’ll have a look at a youtube video as well, though not my strongest area of expertise!