Paccar MX-13 Derate - Regenerations Inhibited and SPN 5246 FMI 0

Question

My 2017 Peterbilt 579 is stuck in a 5 mph derate and won't let me force a parked regen. The dash shows 'exhaust system high temperature' even though it's been sitting for four hours. It keeps kicking out of the service routine after about 3 minutes of high idle.

obd2_owl · Accepted Answer

The issue was a failed Upstream NOx sensor (Part # 22790-5M30C) that was reporting 3000ppm constant. Replaced the sensor, then used Davie4 to perform the 'SCR Soot Level Reset' and 'Reductant System Self-Test.' Once the codes went inactive, I could finally trigger the forced regen. Sensor cost about $450 and took 20 minutes to swap with a 22mm crows foot.

Greg Walters · Answer

You need to check your NOx sensor readings using Davie4. If the inlet sensor is stuck high while the engine is off, it will prevent the regen cycle from initializing because the ECM thinks the catalyst is already overheated.

shoptech_carlos · Answer

Look at the DEF pump pressure during the startup sequence. If it's not hitting 5 bar consistently, it won't even attempt to spray, and the system will abort the regen to protect the SCR brick from face-plugging.

hd_trucker_77 · Answer

When you have SPN 5246 FMI 0, that is the 'Final SCR Derate.' You often cannot get out of this without a software command to reset the derate timers, even if the physical part is fixed.

Paccar MX-13 Derate - Regenerations Inhibited and SPN 5246 FMI 0

Suggest a repair