It's actually a 5 day weekend :D....not sure on plans tho. I'll let you know.

Alrighty... did some work on the X5 yesterday and today. First the good news. Got the front NOX sensor replaced without too much trouble, though my gorilla hands made getting to all the zip ties and clamps for the wiring an interesting and time consuming experience. Also, I'm not one to believe in coincidences but I found a frayed wire on the upstream sensor wiring (body side, not sensor side) but inspected it for a good 10 minutes and could not find any damage to the internal wire shielding. It was just barely rubbing on the front driveshaft enough to go through the outer cable loom. I patched it up and made sure it was secured properly upon re-installation of the "new" NOX sensor.

https://s6.postimg.cc/bzzrb1alt/20180520_114025.jpg

https://s6.postimg.cc/9io03ryf5/20180520_123140.jpg

Comparing the old and new sensors I'm guessing the replacement one I put in is a newer revision than the old, which is good. We'll see what it does when I am able to get the truck back on the road.

https://s6.postimg.cc/gyn9pktu9/20180520_123154.jpg

The bad news. I had the thermostat replaced at the indy I used to work at in December 2017 following a back surgery I had. Normally I do all the work on my vehicles but there was just no way to physically do it for at least a month after the surgery. The water pump on these is mechanical... and cheap, so that's good. The truck is leaking from the thermostat to water pump seam which means I could take it back I suppose and use the warranty on the work.

But, I am sorely tempted to just order a water pump, thermostat, belts, idler pulley, and some other front end maintenance while it's down. I already have the fan pulled and coolant drained so I am thinking I am going to just go ahead and do the work myself. I don't like having others work on my vehicles so I'll just eat the cost of the thermostat work they did. :dunno: Besides, adding the additional maintenance to their workload would incur at least a $600 to $800 repair bill for what, ~$200 in parts.

Yes, I looked into it when one of my NOX sensor was acting up but never spent too much time on it since it was replaced under warranty. If it fails again I'll go to the local GM dealer and take a look.

Cummins/Ram and Duramax/GM both use Continental NOX sensors, now the question is which one has a long enough wire and which one has a connector that works with BMW. The NOX sensor cannot be separated from the control box.

It's hard fro pictures to really see if the connector is the same or not, but they should all have 4 pins: CAN+ CAN- Ground and 12V...

Both of these were 5 pin on the controller to body side. I got resistance on pins 3 & 4. Was the same on both the old and the "new" sensor. The sensor itself had 7 wires going to the control box.

That's very possible that I got the pin count wrong, I was going off of memory.

In any case, I believe it's very very unlike that the controller is what goes bad. My suspicion is that is the actual catalyst element inside the probe that gets poisoned. The NOX sensor effectively works like a wideband O2 sensor with an added step. There's a catalyst inside the probe that takes NO and NO2 and brakes it down into N2 and O2. The sensor then measures the amount of O2 and calculate NOX. All the processing is done in the controller box that sends back to the DDE a processed signal via CANBUS. The DDE doesn't get a raw analog signal from the sensor, but a processed value from the controller.

It's my understanding that there's a baseline calibration done on each individual sensor that is uniquely paired to a controller. I think that's why they are not sold separately.

I'm not really sure there's a way to assess whether a sensor is "good" or "bad" without a known sample to test the reading against.

I'm not sure there is either... at least not without expensive test equipment. I just ohm'd the pins for s's and g's really to see if there would be any differences between to two units.


It's a complex setup for sure. The only real test I am concerned with is whether or not the NOX codes and SES light come back on. :D

To bookend the thread... thanks to Seattle for the sound advice regarding simply picking up a used NOX sensor. Bought a front and a rear for $49 each and replaced the one the code was for. No more code so I'm a happy camper. Will keep the rear as a spare for if/when that one goes out as well.

So I'm going to call this one fixed for the time being. :thumbup:

Thanks to all for contributing and assisting.