Nox sensor seized

[PaulM005]

I had my engine management light come on and off for a number of weeks so got it booked into local MB garage. They came back today to say that the Nox sensor has seized and if they can't get it off without damaging the exhaust then it will be £5500 to replace the entire exhaust. They won't go ahead and try to remove it unless I authorise the full amount. Any advice here??

Exhaust system (inc Emmisions Control) Left nox sensor upstream nox storage catalytic converter Exhaust section due to nox sensor seized All clamps and bolts Both oxygen sesnors

5,596.62 GBP

 

[zipdip]

Well a MB garage is maybe not the best place to get a seized sensor removed,you need a place that will apply heat to the sensor,so if I were you I would ask around locally ,and Welcome aboard.

 

[rf065]

I'd go elsewhere. I could get a custom made stainless steel exhaust for a fraction of £5500.
Apart from that the exhaust is made in sections, so why would they need to replace the whole exhaust? They're not being entirely honest with you.

 

[PaulM005]

Thanks both for the replies. I still need to pay the 180 diagnostic charge but think I will take the car back and look locally for someone who can safely remove the sensor. MB already checked all the exhaust and it's all in working order. Thanks for the warm welcome

 

[PaulM005]

Sorry I should've said its a 2015 e400 coupe petrol so it has a twin exhaust.

 

[TC350]

I strongly suspect that a vast number of NOx sensors are being replaced (at silly prices) when there’s nothing wrong with them. I’m confident that in the majority of cases it’s just a matter of the software detecting the sensor returning a reading out of spec by a small amount for a short time. This registers as a fault.

I’ve found that by cancelling the fault code with a cheap OBD scanner it may come back on after a few days ( or may not). Cancel the code again and it usually stays off for a year or so. I suspect that the out of spec sensor gets cleaned by a blast through the exhaust system. It’s most likely to get contaminated during short journeys.

The problem with Mercedes’ Star computer system is that it will only say that the sensor is faulty when one of the codes pop up. It won’t say that the system may clear itself.

I’d recommend spending £25 on an OBD reader and trying my method. If all else fails, visit an ECU mapper and get them to delete the codes. A decent mapper should know which codes to delete for your car.

 

[BTB 500]

As an aside it might be possible to drill out a seized sensor anyway. I had a DPF temperature sensor go and that's how it was replaced (by an MB dealer, but a commercial rather than car one).

 

[PaulM005]

Adding some screen grabs I took from the MB video to show the condition of the sensor incase it affects any opinions. Cheers

 

[PaulM005]

Screen grabs attached

 

[PaulM005]

The point TC350 made about short journeys could be true. I've had the car 2 years and do mostly short journeys and have averaged 4k miles per year

 

[TC350]

The point TC350 made about short journeys could be true. I've had the car 2 years and do mostly short journeys and have averaged 4k miles per year

Since you have basically the same engine as me (M276) and your usage is virtually identical, I recommend even more that you try my DIY code cancelling suggestion. It won’t do any harm to anything, even if the fault remains for months or even years without being resolved. But it could save you a fortune.

I should perhaps add that I had NOx sensors replaced twice (first under the new warranty and a few years later with a £1k contribution from Mercedes as goodwill. Six years with my “hack” have resulted in no problems and the engine still purrs like a dream.

 

[Railwayman]

Heat is your friend here, play a Map gas torch on the junction between the sensor and exhaust, removed many a seized nut, bolt etc this way, not had a failure yet. Personally would not let a MB dealer service my lawn mower.

 

[Jobsworth]

These can be a nightmare when seized. They aren’t like a lambda sensor, which is just one bit. The Nox sensor is seperate part to the tube nut. The sensor bottoms onto a plate with a hole in it, and the tube nut holds the sensor down tight onto the plate. Applying heat expands everything and actually makes the sensor tighter against the tube nut. I’ve had my fair share of trouble with them. The course I have followed with success on the most troublesome ones is to cut the threaded tube away completely and weld a new one in its place. You can buy new threaded bosses on eBay very cheaply, but you’ll need to be a competent welder