Kenworth T680 SPN 2500 FMI 2 - Aftertreatment SCR Catalyst Efficiency Low

Question

My 2017 T680 is throwing a SPN 2500 fault code along with a derate timer. The truck feels like it is pulling fine but the dash lit up like a Christmas tree and I am worried about getting stuck in 5mph crawl mode.

Sarah Thompson · Accepted Answer

The issue ended up being a failed SCR catalyst brick that had started to face-plug. I performed a 'NOx Conversion Test' using DAVIE software and saw the efficiency was only at 40%. Replaced the SCR Assembly (Part #2109572PE), installed two new Continental NOx sensors, and performed a reset of the learned SCR data. The total repair was about $4,800 in parts, but the truck is back to full power and the code is gone.

hd_trucker_77 · Answer

It could be DEF crystallization inside the decomposition tube. If the spray pattern is wonky, it won't mix correctly with the exhaust gas before hitting the catalyst. Pull the doser and look inside the pipe for white build-up.

fleet_chief_42 · Answer

Check for exhaust leaks between the turbo and the SCR brick. Even a small pinhole leak can introduce oxygen and throw off the NOx sensor readings, triggering SPN 2500. Look for black soot trails around the bellows pipes.

Greg Walters · Answer

You should start by checking your NOx sensors. If the outlet sensor is biased, it will report incorrect conversion efficiency. Use a diagnostic tool to compare the inlet and outlet readings once the SCR is up to operating temperature.

Kenworth T680 SPN 2500 FMI 2 - Aftertreatment SCR Catalyst Efficiency Low

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