Originally Posted by Hbones11

Drove the car for another few hundred miles, didn't see any white DEF residue, but had the P203A/P205B codes appear (never had them previously). After consulting a few Technical Service Bulletins, reading similar blog posts, and talking to some diesel techs I have the following thoughts:



1. I have a hunch my P203A/P205B codes are due to any white DEF residue that is lingering in the system.

2. Based on the codes, I think my issue is related to sensors in the active DEF tank. My understanding is the passive DEF tank does not contain any sensors and only feeds the active tank when it drops below a certain level.

3. I do not believe the sensors in the active DEF tank are toast. I've read blog posts about flushing the DEF tank with hot or warm soapy water multiple times. Some posts have confirmed this fixed the P203A/P205B codes.

4. I haven't had a chance to flush my active DEF tank, but if that doesn't work I don't think you are able to buy just the active DEF tank sensors. This would obviously result in me replacing the active DEF tank to fix any sensor issues (if I haven't found any other avenues to pursue).