[excelblue]

I have a '14 328d with >170k mi, and one day, the MIL came on saying that the NOX sensors were out of range.

I plugged in ISTA+, did the SCR diagnostics, and it suggested replacing the front sensor, and if that didn't work, replacing the rear sensor.

Sounds simple enough, right? Yeah, it was supposed to be simple.

So, I needed the following parts:
13628589846 - front NOX sensor (before SCR)
13628589844 - rear NOX sensor (after SCR)

I go onto eBay and get a new front sensor, installed it: get a code for sensor reading out of range. I take a guess and also get a rear sensor, installed it: get an additional code for sensor reading out of range.

Thinking that those sensors might be problematic, I go to to a reputable reseller and get some "Hamburg Technik" branded sensors. I receive them and was disappointed to note that they were also made in China like the eBay ones, and this time, the rear sensor had a sticker that wasn't even marked. Anyways, I install those sensors, and again, the problems persist. In fact, this time, after the first 100mi, the front sensor would only report 65536ppm and never a valid value.

Anyways, after all of this, I finally ordered some OEM sensors made by Vitesco (formerly Continental) from FCPEuro. I installed those, and finally, they work and the codes go away.

Turns out: the Chinese sensors would take too long to initialize and report 65536ppm for too long while initializing, while also returning implausible results when that figure gets averaged in with the actual values later. The OEM ones report valid values right away.

Anyways, just wanted to share this in case anyone else wanted another data point or had faced similar frustrations.

tl;dr when it comes to the NOx sensors, you really need the OEM (or Genuine) ones or else they'll report incorrect values while being initialized.

[agentorange]

I'm going through the same thing, but at far less mileage. Too much town running, maybe. My independent tech has cleaned the DPF and SCR, he said it was majorly sooted up. He thought he could clean the one sensor, but that plan has failed.

He also says that non-OM sensors are largely a waste of time, and it's not just on BMW diesels. I agree, because a friend went down the same rabbit hole with a gas powered Toyota that didn't play nice with aftermarket sensors.

[FaRKle!]

Good cautionary tale. This is global among all vehicle brands. Only Continental/Vitesco (Vitesco spun off of them) make actual functional NOX sensors and are the OE for everybody. Any other brand isn't worth it.

[agentorange]

Further on new NOx sensors. My independent guy tried cleaning them up to no avail, but even when he fitted new ones he still had issues. He told me he had to take the car to a shop with a better diagnostic machine to get the NOx sensors to calibrate. Any thoughts on that? Would not surprise me given how Audi, BMW, and M-B are trying to exclude everyone except their techs.

[excelblue]

Originally Posted by agentorange

Further on new NOx sensors. My independent guy tried cleaning them up to no avail, but even when he fitted new ones he still had issues. He told me he had to take the car to a shop with a better diagnostic machine to get the NOx sensors to calibrate. Any thoughts on that? Would not surprise me given how Audi, BMW, and M-B are trying to exclude everyone except their techs.

So, he replaced the sensors with OEM (or Genuine) ones, right?

If so, did he remember to do the NOx sensors reset via his scan tool?

I personally requested the reset via ISTA+, but afaik, better OBD scanners and Bimmerlink should also support doing the reset.

I verified functionality by checking for plausible readings on the front (sensor 1) and rear (sensor 2) sensors: they should be close to 0ppm at idle and be in the hundreds of ppm after some some engine load.