2016 Ram 2500 - Stuck in Derate - P208E and P218F Reductant Codes

Question

Running down the interstate and the EVIC popped up with 'Exhaust System Service - See Dealer' followed immediately by the 5 MPH speed limit warning. I've been fighting these DEF issues for months. The tank is full of fresh fluid and the pump sounds like it's priming, but the codes won't clear even with my scanner.

I already replaced the DEF pump assembly last year thinking that was the weak link. I'm afraid the SCR catalyst is cooked or the injector is totally gummed up with urea crystals. I need to get back on the road for a haul tomorrow.

BMW_Bjorn · Accepted Answer

✅ Confirmed fix: The issue was a crystallized DEF injector and a collapsed suction line. Even though I cleaned the tip, the internal solenoid had failed due to backpressure. Replacing the DEF injector (Dosing Valve) and performing a 'Reductant System Tamper Derate Reset' using a high-level scan tool cleared the 5 MPH limp mode immediately. Always check for urea crystallization inside the decomposition tube where the injector sits; if that's clogged, the new injector will fail too.

NoStartNoel · Answer

Check the wiring harness near the frame rail for the DEF injector. Those wires are notorious for rubbing through on the 2013-2018 chassis, causing intermittent shorts that flag the P208E. If the harness is good, you might need to perform a stationary regen and a DEF quantity test via WiTech to see if the pump is actually hitting the required pressure.

2016 Ram 2500 - Stuck in Derate - P208E and P218F Reductant Codes

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