The engine light came on on my BMW 1 series (118d – F20, 2019) the other day, and a fault code reader (Bimmerlink in my case) showed the following error:
Error 280D00 – the NOx sensor in front of the DeNOx-Kat has given an invalid signal for too long.
I decided to take a bit of a punt and just try swapping out the sensor myself and not do any other diagnosis. I had the same issue a while back on the rear NOx sensor (the one behind the catalytic converter) and a garage charged a fortune to diagnose and change it, and being particularly tight, and comfortable working on cars, I decided to give it a go.
I first looked up the part on realoem.com to try and work out where it physically was. Searching for NOx, I got this:
There it is, marked ‘1’ in the diagram. Seems to be right at the front of the exhaust, so let’s go hunting.
The first thing I did was to jack the car up on the front centre point as high as I could get it, secure it on jack stands, then remove two undertrays to get to the sensor.
And here it is in the flesh!
The cable coming from the sensor goes across the car from one side to the other, to a connector on the left. It’s still accessible underneath the car no problem, it thankfully doesn’t disappear up into the engine. Here it is:
It’s in a tricky position to remove. It’s too tight to get a socket onto (even a special O2 sensor socket). All I could get onto it was a 22mm open-ended spanner. I didn’t want to damage the flexi to the left so you can’t go mad hanging off it, but it came undone fine after a good soak in WD40 and a bit of sweating, so all was good.
Time to look up the part number at BMW and see how much a new sensor costs.
FIVE HUNDRED AND FORTY SEVEN POUNDS!
Absolutely mental.
As you can see from the picture above, the sensor is a Bosch part, with a BMW logo also on it.
I did a bit of digging and found the original Bosch part, without the BMW logo, on eBay, for a much more reasonable (but still pricey) £221:
When it arrived, it certainly looked the part. Exactly the same as the BMW one, but without the BMW logo. Lovely stuff!
It was a bit of faff getting the new one in as I’m quite anal about clips and cable ties, but I managed to snip the original ties off the old clips, then reuse the clips and feed new cable ties through to keep everything as close to original as I could.
Apparently it is important to reset the previously learned adaptions in the car when you replace the NOx sensor, and thankfully I was able to do this with my Foxwell NT530 code reader. It took a bit of digging, but under the Service function, then SCR System, I had an option to reset adaptions.
Job done!!
This gives me at least 4 weeks of constantly reminding my wife of the hundreds of pounds (could even be £1,000 at the main dealer) I’ve saved us in doing the job myself, and it wasn’t bad at all. Quite pleasant infact in the sun with a nice coffee.
Although this has specifically looked at a BMW 1 series, the procedure will be almost identical across most of the BMW range.
But that’s not all…
Given my background in electronics (explore this site), I decided to take apart the control box connected to the old sensor and it is bananas.
The circuit board is a hybrid design, with bondwires connecting bare dies onto the circuit board, plus a load of ancillary components. There looks to be perhaps a couple of FETs at the bottom, then presumably a microcontroller, plus another couple of complex ICs. Quite interesting, actually. It’s crazy to think that this is just one of hundreds of sensors in a modern car.
Perhaps it is worth a few hundred pounds, afterall.