I have a 2021 High Country, 3.0l turbo diesel. At about 1000 miles, I got the dreaded CEL with a P1488 code. My dealer when thru all the required attempts to fix it; torque the particulate sensor, torque exhaust pipe clamp, add 'Tiger Tape' to the exhaust pipe joint, smoke test for exhaust leaks, replace the flex joint.....all to no avail. I was always skeptical about the exhaust leak theory. After all, how could the truck know there was a small exhaust leak to atmosphere?? In total, my truck was at the dealer service 7 times with no resolution. Each time they reset the code and the CEL always came back on within several hundred miles. I was finally able to get the regional service tech representative involved. He instructed my dealer to replace the whole exhaust system, including the cat convertor. Probably $2-3000 in parts. That has solved the problem.
Apparently there were some manufacturing variances with the exhaust pipe joint aft of the particulate sensor. This allowed a small air leak 'INTO' the pipe between exhaust pulses which confused the emission controls. A small number of exhaust pipes with this slightly defective joint all showed up with this same problem. I also had a particulate sensor that was occasionally sending bad data. This was identified using a data collector on a 10 mile drive.
I've since discussed this issue with an engineer friend who specializes in engine emission certification. He says the very first thing they do in preparing for a test run is pressure test the exhaust system and repair even the smallest leak. Otherwise, they would never get a consistent result. So, this rather implausible solution has some basis in science.
I've put about 10k miles on it since the fix and no CEL. Yea! I commend my dealer for sticking with me on this. They were carefully following the various Tech Bulletins and instructions from Detroit and always accommodated my schedule and provided a loaner car when there weren't many available at the time.
