XSeries-forum

I can see the two sensors ahead of and behind the cat, not hard to get to. But each has a really long cable to a squarish control/electronics module that are completely hidden. No idea where they are and how much work it will be to get to them. Anyone replaced these before? Trying to avoid a MASSIVE repair bill from the local dealer. Over 3k$ to replace!!! I already bought a pair of sensors for less than 1/10th of that.

Thanks in advance for any help to solve this.

According to what I can see, it connects directly to the Digital Diesel Electronics module (ECU) in a waterproof box just ahead of the scuttle.

Pins 8 & 9 on connector X20008. Wire colours are Yellow/White and Brown/Violet. Sensor has an intermediate connector close by the sensor itself X2451 and the sensor is B2451. Wiring comes back to the X20008 on the DDE.

I’m pretty sure that’s not correct because there are modules on the ends of the cables that mount to the body somewhere. The cables are slightly shorter than 3’ each, not long enough to get to the engine compartment.

This is what the BMW TIS says against NOx for the E70 35D with the N57 engine. The wiring diagram has no modules between the sensor and DDE unit itself, just a connection joint partway on the body. What market are you in? As in where in the world….in case it makes a difference. Some versions have SCR (AdBlue) control. I’ll have another look just in case.

If there is a module then it might be in the transmission tunnel to the right of the propshaft (post cat sensor). The pre cat sensor only shows a direct connection via B2451/X2451 then as above.

These apply to the N57 engine, not the M57 according to what I have. The M57 doesn’t have NOx sensors (at least none are showing in the documents) but does have pre/post cat temp sensors. The wiring for those goes up to connector blocks as below…..
Beyond that, I can’t help any further as there’s nothing in my documents.

You can try sourcing a copy of the TIS for the right year(s) on places such as EBay. Not expensive.

After that then BMW make the TIS available via a pay-per-view system, but it can get expensive!

https://bmwtechinfo.bmwgroup.com/#/login

I’m in the US and yes it has SCR. Here are the sensors You can see that these things have mounting holes and output connectors as well. I’m trying to find where those modules mount as I know there are heat shields that have to be removed at minimum. Thes NOx sensors are before and after the SCR cat.

I will see if I can get the proper TIS on eBay. Thanks for that tip.

OK, with your images of the sensors, the only match that I can find it this one…..looks to be looking up into the transmission tunnel from below. There’s a bracket with a shape that looks like what you’re hunting…it looks like it might be hidden by heat shielding?
This is the underneath of a US spec E71, which is the same floor pan with a different rear diff, but might help locating the sensor blocks?
Image courtesy of European Auto Source

Thanks a bunch. Yes I’m pretty certain I have to pull off heat shielding. Trying to see if I can do it without dropping the prop shaft!!