Oxygen sensor and Nox sensors failure - need any advice please

[Jai]

Hello everyone I was wondering if anyone could help me, I have a 66 reg bluetec Mercedes c220d with 40000 miles on, my car also has a stage 1 remap on it that I’ve had for about 6-7months now. I’ve recently just had an engine management light come on to therefore find out that I need a new oxygen sensor and 2 new nox sensors. I find it strange how an engine management light has just randomly told me I have got 3 faults that I need replacing. Can a oxygen sensor cause a engine management light? If so why hasn’t that come up first or vice versa if it was one nox sensor that went first why didn’t the engine management light come up if that failed, why has all 3 come all at once, I’ve recently just had my mot done too and passed it. Is there anything that I am missing? I have been to about 3 different garages for them to tell me they can’t do anything and to take it to a Mercedes specialist who then quoted me 1400 pounds to get it all replaced without doing a wiring diagram, does anything think I should take it Mercedes dealership instead and find out exactly what the problem is, has anyone else had this problem, any advice would be really helpful, thank you!

 

[V6quadcam]

I have '65 C220D BlueTech and had the management light come on, I borrowed an OBD tester and confirmed it was the NOX sensor. My local service company advised me to go to an MB specialist (not main agent) the problem is that there are a number f NOX options and associated software upgrades which the specialist can evaluate and give a 2 year warranty for over £400.
If you can get your hands on OBD tester you could clear the faults and wait to see if they return and then take the necessary action.
It is possible that your remap could have been the cause of this fault.
One of my cars is very sensitive in slow traffic and the fault comes up but clears after a while.

 

[markjay]

With regards to your question how come that all three sensors failed at the same time, the answer might be that the first two failures occurred earlier but didn't bring-up the EML, the last one that failed, did. When the codes are read all existing faults show-up. STAR will show which fault caused the EML, but that's academic.

On a related note, has the car been to an MB dealer recently? There's an engine management software update that dealers carry-out while servicing Diesel cars, which may cause sensor failure.

And last, some forum members had sensors replaced by MB free of charge, so it may be worth trying your luck with an MB dealer first, though you should try and avoid hefty diagnosis charges.

 

[Jai]

I have '65 C220D BlueTech and had the management light come on, I borrowed an OBD tester and confirmed it was the NOX sensor. My local service company advised me to go to an MB specialist (not main agent) the problem is that there are a number f NOX options and associated software upgrades which the specialist can evaluate and give a 2 year warranty for over £400.
If you can get your hands on OBD tester you could clear the faults and wait to see if they return and then take the necessary action.
It is possible that your remap could have been the cause of this fault.
One of my cars is very sensitive in slow traffic and the fault comes up but clears after a while.

I have tried to clear out the codes as I got recommended by a garage. The person who I went to completely messed up, I thought it’ll be an easier route if I got the nox code deleted but little did I know that it would go horribly wrong. So he gave me the car back in the way that I sent it too him, anyways a few days later a battery light came on saying “stop the vehicle leave engine running”. So I got that checked out and mechanic told me that the battery is perfectly fine. I still drove for a week but the battery kept on coming back up so I decided to buy a new Bosch battery. Car feels so much better, start stop works again now. But yes engine management light is still on and the Mercedes specialist have quoted me 1400 to get them all fixed. I don’t know if I want to be spending that kind of money on a car that’s only 4 years old and has only do 40000 miles on.

 

[Jai]

With regards to your question how come that all three sensors failed at the same time, the answer might be that the first two failures occurred earlier but didn't bring-up the EML, the last one that failed, did. When the codes are read all existing faults show-up. STAR will show which fault caused the EML, but that's academic.

On a related note, has the car been to an MB dealer recently? There's an engine management software update that dealers carry-out while servicing Diesel cars, which may cause sensor failure.

And last, some forum members had sensors replaced by MB free of charge, so it may be worth trying your luck with an MB dealer first, though you should try and avoid hefty diagnosis charges.

I don’t know what star is, but no I haven’t been to a Mercedes Benz main dealer yet just the specialist, I think I may chance it there as you have said it could be engine management related. I think it’s the best option for me at the moment otherwise I will have to spend quite a bit of money.

 

[andy27168]

Hi,
STAR is the Mercedes diagnosis computer system, directly connected to the Fatherland.
Don't volunteer any info about having had the car remapped, it will almost certainly effect the way they deal with you and any FOC or good will repairs they may make on the NOX sensors, and be prepared that you might lose you're remap as they may update the ECU software in line with the recall.

 

[Jai]

I’ve called up Mercedes and they have agreed to get my car In for a diagnostic and to see if they can get a good will gesture as I have explained the situation to them. Would you also agree that a car that’s only 4 years old with 40k mileage shouldn’t have these problems, an oxygen sensor is suppose to last 60k up until the life of the car if kept in really good condition and I’m not sure about how long nox sensors are suppose to last as they are new to me. Anyways I’m booked in for Tuesday wish me the best of luck and thank you so much everyone for the advices! I’ll update everyone and tell you how it went, could be good or very bad! Fingers crossed

 

[Gazwould]

Goodbye remap..

 

[DrNick]

I’ve called up Mercedes and they have agreed to get my car In for a diagnostic and to see if they can get a good will gesture as I have explained the situation to them. Would you also agree that a car that’s only 4 years old with 40k mileage shouldn’t have these problems, an oxygen sensor is suppose to last 60k up until the life of the car if kept in really good condition and I’m not sure about how long nox sensors are suppose to last as they are new to me. Anyways I’m booked in for Tuesday wish me the best of luck and thank you so much everyone for the advices! I’ll update everyone and tell you how it went, could be good or very bad! Fingers crossed

Sadly, because you've had it remapped (tinkered with) a 4 year old car with 40,000 could easily have these problems. You've changed it from what Mercedes designed (with years of testing and backed up with a warranty) to something else with very little testing and backed up by no warranty of any worth.

We will never know now for sure if the failure is due to dodgy oxygen sensor failing early or if it was a good oxygen sensor being operated outside its design envelope, whatever you may think.
Lets hope Mercedes are in a good mood because I think you've been unlucky, but really its "buyer beware" here.

 

[DrNick]

As another thought, did you get the messages cleared after you changed the battery? Its possible that if the battery was on the way out, these error messges may have been generated by mistake and the sensors are actually ok. I'm sure that Mercedes will probably do this on the diagnostic and look at live readings, but it would be worth telling them that you've changed the battery because of other messages so they are aware. Don't want the sensors changed if they are actually ok!

 

[Jai]

Hello guys completely forgot to reply here but I managed to get it all fixed for free! Mercedes was lovely about it and even gave me a free check even though I was one year out of warranty. Thank you guys for the advice.
Oh yes also I put the remap back on, my car feels faster than last time, weird right..