2020 Cascadia One Box Keeps Falling

Everything upstream needs to be in good working order for the emissions system to work properly. No intake air leaks or exhaust leaks. Best to have the system pressure tested 15-20 psi with smoke. Valves adjusted properly, injectors metering the proper amount of fuel, good compression and not using excessive oil.... Has anyone hooked up a laptop and checked the data?

 

What about the doser and the doser block? Heat comes from fuel.

That's weird about the ECM. You getting any CAN bus faults?

 

The issue needs to be escalated. Someone needs to call Freightliner regional or corporate. There was an issue with a Volvo that no one could fix or knew what to do with. Numerous dealers and shops were involved. After contacting regional they knew right away that replacing a harness would solve the problem and it did. Another basic thing is that they should have checked for recalls and service bulletins. Who knows if the right injectors were installed. Try disconnecting all the batteries and power to reset things and see if that makes any difference.

 

Most of those electrical gremlins can be explained by water intrusion or corrosion. The switch panel in the bunk tends to corrode because of condensation. I have the fuse pulled on my bunk fan right now. Also, ELD's or ScanGauges or anything plugged into the data port can cause weird communication issues if there is a short. I had that happen with a K&R Scan Gauge once.

None of what you described sounds like anything that would affect the after treatment system though. There is an after treatment computer which could if it is failing. Also, you need to be sure about the doser and doser block. Heat is caused by fuel and those two components dispense fuel. I would think the dealers would have checked all that though.

You still haven't told us what fault codes it's throwing. Does you engine shut down from the excess heat in the onebox? It should shut down at 1400 and throw codes.

 

SPN 521052 FMI 31 - a derate advisory
SPN 521049 FMI 31 - poor NOX reduction despite maximum DEF dosing.
SPN 520329 FMI 31 - DEF pump overspeed. DEF Leak or blocked DEF doser.
SPN 3216 FMI 16 - Inlet NOX sensor plausibility error. Soot accumulation, bad sensor, or bad wiring.
SPN 3719 FMI 31 - DPF soot high. Needs a successful regen.
SPN 5443 FMI 16 - indicates High Hydrocarbon (HC) Absorption in the Diesel Particulate Filter (DPF) on Detroit DD15/DD13 engines, signaling that too much fuel has entered the exhaust, likely due to excessive idling, low exhaust temperatures, or failed regeneration attempts. It requires a parked regeneration to clear.

It looks to me like your temperature issue and other issues may be derivative and caused by failed regens. I'd work the DEF issue first. There is a test you or a shop can run using the DDDL software to measure the DEF flow. But check for leaks first.

Also, visually inspect the DEF pump. You have to remove the metal shield to see it well. When those pumps go bad they blow a seal and it looks like they have sugar caked all over the outside. Change the DEF filter while you're there.