[herrbrahms]

Wow, nice job to the OP on diagnosis and resolution. It's even more impressive considering that this is your first diesel with urea aftertreatment.

As far as preferred DEF brand, don't be suckered into thinking that expensive is better. It isn't. Walmart DEF is the same 32.5% urea in deionized water that AdBlue is or any other branded product. The stuff is perishable, though, especially with light and heat. It noticeably degrades above 30C. Try to get the freshest supply you can, particularly as you live in a hot climate.

You might be best served hitting up a truck stop with your own opaque container as that is continuously replenished. I've never tried it myself as Walmart has always worked out for me, but then again I don't live in a furnace like you do.

My hypothesis based upon incomplete information is that the previous owner of your car let it sit in the heat with relatively low miles since the last refill. If you got a CarFax before purchase, see if that's plausible from the report. If you can keep the car in a cool garage that will help, and I would definitely keep any reserve DEF you buy within the air conditioned envelope of your house.

[ululi1970]

The car sat for a couple of months before I purchased. As part of my diagnostic, I did check the DEF fluid it was in, and it was on the lower side of 32.5% but still within specs. It did smell of ammonia, so I replaced it anyway, but obviously the real culprit was the Nox sensors.
Hard to avoid heat here. Unfortunately, my garage does not have AC (may install a minisplit in the future), so in the summer the minimum temperature the car see is upper 90s at best, but I think this summer in July the temperature in the garage never went much below 98F.

I wish they had thought of a way to drain the DEF tanks. The passive one is actually pretty simple (just unplug the inlet pipe on the transfer pump). For the active, a long hose with a manual pump is needed, or remove the metering pump and let it drain.

The lesson learned is to run the ISTA diagnostic completely, and repair/fix/replace what can be repaired before showing up at the dealer for the Nox sensors. I am sure that had I not replaced the EGT sensors, they would have charged me an arm an a leg for that, before even touching the NOX sensors.

The silver lining was driving the 228i loaner up the White Mountains. That was stupid fun.

[herrbrahms]

As far as draining the tanks, are you motivated to add a drain to the active one yourself or do you no longer foresee a need?

I don't know what it is about ISTA but the process terrifies me. I have the cable, I have the old laptop, but still...I think there's a couple of easy steps I missed back when I tried to teach it to myself years ago. Online tutorials weren't enough to get me all the way so I threw in the towel.

I have the Foxwell scan tool which does a decent job, but for serious coding I rely upon the skills of those wiser than me.

[ululi1970]

I found using ISTA/D pretty easy. The hardest part was to configure the Ethernet port for the ENET cable correctly. There was a YouTube video that went over the steps. Once that is done, the interface is a little dated but not too bad. It is my understanding that it is hard to mess things up with ISTA in diagnostic mode. Different story in programming mode, but I do not have that option installed.

[herrbrahms]

Good deal. If you'd like to link to the video that worked for you, I might give it another try once I finish up with my current projects. My weather window for getting under vehicles is rapidly closing here in the soggy NW.