I had the same diagnostic done and was told it was the nox sensor my car is a 118i first thing on a morning it is very sluggish and makes a loud noise like a bad Diesel engine then after 30 seconds it jerks the warning light comes on then it runs fine. I've now taken the car to a proper BMW dealer for a diagnosis on the engine light coming on and I'm a bit baffled. Warranty Coverage: In case a purchased product becomes faulty during its warranty period, for reasons unrelated to your acts, omissions or misuse of the goods, you must promptly notify us and fill out a warranty claim form. Should my one question as to why my engine light comes on not simply be answered by one diagnostic with the appropiate software?

I would doubt the NOx sensor is the cause of this - which is why I'm dubious your mechanic has told you the right information - and I'm also surprised that the diagnostic has shown a failed sensor, yet (without anything to suggest otherwise) he's saying he doesn't think that is the issue.

I replied that my question was simple from my perspective, the engine light comes on and I want a diagnosis from proper BMW software as to why but now I feel they're essentially telling me they need to tackle the fuel pressure sensor first before they can further diagnose? There is no eml, basicly was serviced by a specialist local to us a few months back who told her there was a good few fault codes on the ecu, took it to BMW today who said the nox sensor was at fault. All was well then the engine management light came on again took it to my mechanic to give it a good once over indicators are nox sensor.

Also have a poke around and check the air intake system for splits/leaks, as this will give a rough idle as well. Park’s of Hamilton (Townhead Garage) Limited, Douglas Park Limited, and Park’s (AYR) Limited, are Appointed Representatives of Park’s of Hamilton (Holdings) Limited, of 14 Bothwell Road, Hamilton, ML3 0AY, which is authorised and regulated by the Financial Conduct Authority (FCA) as a credit broker. I used them a couple of times for a few of my cars, and they seemed straight enough about what the issues were.

I just came of the phone with them and they said 'it's the fuel pressure sensor and every other fault codes follows from here'. The past week this has now been backed up by an engine warning light coming on and the engine being even more restrictive until i can pull over and turn off the ignition. Either a) exhaust camshaft sensor has failed and needs replacing (unlikely), b), your timing chain tensioner needs replacing (very likely), or c), your timing chain itself has stretched (possible). If he has decent diagnostics, it will tell him what is wrong with the car - there will be no guesswork involved.