Engine Diagnostic/AD Blue warning just after a service

[CaptainBirdseye]

Seven year old C class with 59000 miles on the clock given an A service February 9th by Arnold Clark Mercedes Benz Aberdeen.
After 6 days and approx. 80 miles driving later the engine diagnostic warning light came on and an AD Blue warning message came on.

Four years ago exactly the same thing happened after a service with MB Aberdeen. At that time it was checked out by MB Aberdeen and the explanation was that the air filter installed had some compatibility issues with the NOX sensor(s).
The issue was resolved at no charge to me.

This time the explanation is that it has nothing to do with the air filter and solely a problem with the NOX sensor(s).

I explained to the service manager that it seemed too much of a coincidence that just after the car is serviced exactly the same problem has surfaced.

I know nothing about how the systems work and have to rely on what I am being told by the experts. I told them I don’t buy their explanation this time around. They do not want to know about the fact that in my opinion it is too much of a coincidence that the same fault occurs immediately after a service and it will be at my cost this time to resolve. Can anyone shed any light on this?

 

[markjay]

This is a very common complaint.

It is likely that the dealer has applied the 'Dieselgate' software update to your car's engine's ECU.

These updates are known to cause NOx sensor faults.

To be precise, the software update does not actually harm the NOx sensors, instead what happens is that the new software uses a narrower value range to judge is the NOx sensor is faulty or not. So a NOx sensor that worked fine with the old software, will be flagged-up as failed with the new software.

Unfortunately, the 'Dieselgate' software update cannot be undone, and you can't ignore the MIL either, because it's an MOT failure (or worse, it could just put your car in 'limp mode').

The solution is to replace the NOx sensors with a modified version that has been adjusted to work with the updated 'Dieselgate' software.

The issue is that it's an uphill struggle to get the dealers to accept responsibility. In some cases, dealers have been known to replace the NOx sensors FOC following the 'Dieselgate' software update, but in most cases they refuse to do this for free. If they refuse a free repair, you can either try and negotiate a good-will contribution with the dealer, or just take the car to a reputable independent specialist and get it repaired there.

 

[CaptainBirdseye]

This is a very common complaint.

It is likely that the dealer has applied the 'Dieselgate' software update to your car's engine's ECU.

These updates are known to cause NOx sensor faults.

To be precise, the software update does not actually harm the NOx sensors, instead what happens is that the new software uses a narrower value range to judge is the NOx sensor is faulty or not. So a NOx sensor that worked fine with the old software, will be flagged-up as failed with the new software.

Unfortunately, the 'Dieselgate' software update cannot be undone, and you can't ignore the MIL either, because it's an MOT failure (or worse, it could just put your car in 'limp mode').

The solution is to replace the NOx sensors with a modified version that has been adjusted to work with the updated 'Dieselgate' software.

The issue is that it's an uphill struggle to get the dealers to accept responsibility. In some cases, dealers have been known to replace the NOx sensors FOC following the 'Dieselgate' software update, but in most cases they refuse to do this for free. If they refuse a free repair, you can either try and negotiate a good-will contribution with the dealer, or just take the car to a reputable independent specialist and get it repaired there.

Thanks very much for that. I shall be informing the dealer of your explanation. They are either incompetent or trying to pull the wool over my eyes.

 

[markjay]

Thanks very much for that. I shall be informing the dealer of your explanation. They are either incompetent or trying to pull the wool over my eyes.

You'll need to get them to confirm first is the Dieselgate software update was indeed applied to your car during the last service.

Keeping in mind that while the Dieselgate update can cause NOx sensor failure, NOx sensors can so fail for a range of other reasons.

So if they deny applying the Dieselgate software update, then you won't be able to get them to admit liability.