Here’s the tip to solve 2013 LML Duramax emissions light and fault codes P204F and P20E8 problems.
The first issues that came up was the CEL with P204F and P20E8 (Pump performance and Reductant Pressure Low) and then the emissions light came on a day or 2 later with the “Service Emissions Fluid System” message.
The mileage warning for DEF had flashed the week before and gone away, so I just figured it may have run out somehow without the usual mileage countdown. I added a jug of DEF to it and drove it hoping it would clear. I made it to around 20 miles left on the 65mph restriction before I could get a chance to troubleshoot. I already had done some research and had a spare pump and tech2 capabilities (Using wifi VXdiag vcx nano gm obd2 connector from vxdiagshop.com) in case I didn’t see an obvious fix.
I dropped the DEF tank, and it was empty when I took it down. The DEF discharge line on the pump had popped off allowing the DEF to just pump out unrestricted on top of the tank (the inside of the connector was a little mangled, probably it’s previous repair at the dealer). I removed the old pump (it was probably fine) and primed and installed the new one. I added a jug of DEF to the tank and propped it up on the floor and tested it before installing in case I had more issues to fix.
I ran a leak test and the pump immediately built pressure above and then steady at 500 kPa. I worked through the service bulletins for these by running the Reductant System Malfunction Warming Test. I ran it multiple times but the light remained on. I ran the Reductant Fluid Quality Test, which runs the rpm about the same as a Service Regen. After running these tests the emissions light still remained on. One of the bulletins had said to conduct a road test, so I put the DEF tank back in place and took it for a ride. I romped on it off and on for around 3 miles, and then the emissions light cleared. I didn’t clear the CEL with the scan tool after that, I wanted to see if it would clear itself, and it did after a couple of days.
I would load vxdiag programs on a computer with no personal info. The GDS2 icon loaded and then disappeared due to anti-virus Trojan detection). Luckily I just needed the Tech2 programming because my truck is 2013. (The last available year that showed as an option). Read the vxdiag reviews for how to get the programs to load/open/work correctly.
The tank is easy to drop and reinstall. Having a floor jack to hold one end and help push up the straps was helpful.