I have a Peterbilt with a px-9 engine which is what im assuming just the same as a L9 cummins with code spn 3521 fmi 18. im sure it is pointing out to be an issue with the def system. i have tested the def with a refractometer and it shows it is fine and did do a change in the def filter as well. has anybody else have an issue similar that can be of some help. i cleared the code but noticed it has returned..
The quality sensor is part of the smart unit (tank level, temp, and quality) so generally it is either a DEF quality issue or the sensor is bad, which is common. they were on national backorder last I checked on one but its been a while, hopefully supply has gotten better.
I was scared it would be that as i have already changed one in the past with our other trucks and they do not run cheap at all. considering it is such an extremely expensive part. i would of thought they would atleast fix the issue if its so common a part that goes bad..considering the costs..
How do you like the PX9 other then the DEF issues? Thinking about a Peterbilt 337 with the PX9 and 10 speed. But it does not have the DEF tank on it.
