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International Automotive Technicians Network
Re: Mack MP7 Stuck in DEF Derate
Posted to HD/Fleet Forum on 1/18/2024

Hi Stephen,

Have you checked the DEF fluid quality with a refractometer? Maybe someone thinned the mix with a lot of water. The tank sensor does not like corrupted or thinned DEF fluid.

Next item would be to run a manual scanner DEF injector flow test in a... Login to read more.