Is there a way to identify which NOX sensor has failed?

[spirituscorpus]

Purchased an approved used C200 in March 2019 and just two weeks before the 18 month (August 2020) warranty ran out the engine management light came on and the dealer luckily replaced the NOX sensor FOC.

Fast forward to December 2021 and again the same thing. Engine management light comes on and the code reader I used throws up "Nox Sensor Circuit Bank 1" error code.

I've read that there can be issues regarding these sensors with MB and that with a full service history they MAY replace FOC...even out of warranty (the car has only done about 5k miles since the last time the sensor went).

A phone call to the dealer confirmed my fears as they said there are two sensors and it may be the one which wasn't replaced by them in 2020.

I would welcome any advice but specifically surrounding the error code. Does "Bank 1" identify which sensor is triggering the fault or is that a generic reading?

I would love to trust my MB dealer but it would be very easy for them to say yes, it's the other one which has gone....bend over now!

 

[onefortheroad]

There's a pre dpf and a post dpf sensor . The old one would maybe look older to the new one on inspection

 

[malcolm E53 AMG]

If the car has FMBSH I would ask for a contribution from MBUK if it is the sensor that hasn’t been replaced. MB are having a lot of sensor failures with ADBLUE cars and for them to be failing on >2015 cars the quality is just not there and you would expect a contribution especially on a <50k miles car

 

[mioba]

If you know what you are looking for get under the car and mark the new sensor (should be visible). you will then see what they have changed.

Regardless it will need doing and the part is the most expensive not the job itself.

Id be arguing it shouldnt fail on such a new low mileage car with I assume FMBSH

 

[supernoodle]

To answer the OPs question, "Bank 1" doesn't help you here. That fault description doesn't look complete, normally it would be of the form Bank x Sensor y. Bank is used to detemine the individual cylinder banks on a V engine. Even in a V engine the aftertreatment is normally downstream of where they have combined into a single pipe, so they will be Bank 1 too. If you do have multiple banks, Bank 1 is the one that contains Cylinder 1.
Sensors are numbered from the most upstream position. So for an intake, 1 is nearest the air inlet, in an exhaust, 1 is nearest the engine.

 

[spirituscorpus]

Sorry...I should have mentioned it is a petrol. I believe the majority of nox sensor problems seem to occur with diesel but sadly not in my case.

Yes, the car has a FMBSH and only 20,000 miles on the clock. However, I fear if it is indeed the "other" Nox sensor then I will probably be charged

 

[Steve@Avantgarde]

You don't say whether your car is a petrol or diesel, but petrols only have 1 sensor. If its a diesel it has 2 sensors and both should have been replaced as well as the software being updated. You may even find thats the reason for the fault.

The reason it says circuit bank 1 is because it refers to the first bank of cylinders. Now you only have 4 and its not a V so its fairly straight forward, it means that you only have to look for the sensor on the only exhaust! The reason it states bank 1 is because MB make V engines and use the same sensors on each bank of cylinders so it already has a software string in the engine ECU for 2 banks of cylinders, its just on 4 cylinders its progammed not to look at that side of the ECU but all components used are labelled electronically as bank 1.

Confused? Thats why I do what I do!

 

[spirituscorpus]

You don't say whether your car is a petrol or diesel, but petrols only have 1 sensor. If its a diesel it has 2 sensors and both should have been replaced as well as the software being updated. You may even find thats the reason for the fault.

The reason it says circuit bank 1 is because it refers to the first bank of cylinders. Now you only have 4 and its not a V so its fairly straight forward, it means that you only have to look for the sensor on the only exhaust! The reason it states bank 1 is because MB make V engines and use the same sensors on each bank of cylinders so it already has a software string in the engine ECU for 2 banks of cylinders, its just on 4 cylinders its progammed not to look at that side of the ECU but all components used are labelled electronically as bank 1.

Confused? Thats why I do what I do!

Thanks Steve. I have mentioned it is a petrol.

Are you sure petrols only have one sensor though? The dealer told me yesterday that there are two.

And yes....I am confused!

 

[Jagb]

Good morning all
I purchased a c200 petrol Mercedes-Benz from Cambridge in 2018 registered in 2015 used car. It is under a service plan for 4 years my issue is I have had both NOX sensors replaced in a period of 2 years 1st 2019 and the second in 2020 now one has failed showing
Bank1 Sensor 1 I only drive 5000 a year the car is well maintained Mercedes have said as I had a extended warranty they will not give any thing towards it they also want £120 to check which one is faulty
Can anyone help with advise.

 

[LostKiwi]

Thanks Steve. I have mentioned it is a petrol.

Are you sure petrols only have one sensor though? The dealer told me yesterday that there are two.

And yes....I am confused!

Wouldn't be the first time the dealer 'has got it wrong' - especially if it means they can charge you again!

 

[Jagb]

My current mileage is 51200

 

[Jagb]

Wouldn't be the first time the dealer 'has got it wrong' - especially if it means they can charge you again!

I was told 2 sensors

 

[star]

One sensor on a petrol.

 

[Jagb]

One sensor on a petrol.

My last one was replaced in 2020 June so they should cover it but the dealer did say 2 sensors one in each exhaust

 

[star]

What model do you have?

 

[LostKiwi]

You have now had two trusted and respected independent specialists (one of whom I entrust my SL to and the other who the previous owner of my SL entrusted the same car to) tell you you have one sensor.

Your car is a C200 so is a 4 cylinder therefore only has one exhaust irrespective of the number of tail pipes.

 

[Jagb]

You have now had two trusted and respected independent specialists (one of whom I entrust my SL to and the other who the previous owner of my SL entrusted the same car to) tell you you have one sensor.

Your car is a C200 so is a 4 cylinder therefore only has one exhaust irrespective of the number of tail pipes.

Thank you Steve
I'm new to all this the Car was for my retirement and have been disappointed now I will confront Mercedes you have given me hope really appreciate it can i also ask you my auxiliary battery malfunction message comes up on the dash board do you think i should get it fixed from mercades or an independent garages as i have lost comfidence any idea of cost also i live in the midlands

 

[mioba]

I was told 2 sensors

The point LK is making is that some customers are non the wiser......

 

[mioba]

Thank you Steve
I'm new to all this the Car was for my retirement and have been disappointed now I will confront Mercedes you have given me hope really appreciate it can i also ask you my auxiliary battery malfunction message comes up on the dash board do you think i should get it fixed from mercades or an independent garages as i have lost comfidence any idea of cost also i live in the midlands

Do it, confront the dealer and ask then to show you on the parts list diagrams where the 2 sensors are.....or look and conform yourself by pumpiing your vin into the likes mb teil katalog, its all there

 

[Jagb]

What model do you have?

C200 AMG 2015 petrol