Aftertreatment
What is an engine derate and how do I clear it?
A derate is the ECM protecting the engine or forcing an emissions repair. There are two kinds and they clear very differently.
The answer
The two kinds
- Emissions derate — a staged countdown (often 55 mph, then 25, then 5) caused by DEF level, DEF quality, SCR efficiency or an ignored regen. It clears when the fault is repaired and the ECM verifies the fix.
- Engine protection derate — oil pressure, coolant temperature, coolant level or intake temperature out of range. This one is telling you the engine is about to be damaged.
What to do roadside
- Read the code before anything else. Engine protection is a stop-now situation; an emissions countdown usually gives you miles.
- Check the simple stuff: DEF level, coolant level, oil level, obvious leaks.
- If it is emissions and the truck will still run a parked regen, get to a safe flat spot and run one.
- If it is engine protection, shut down and call for service. A tow is cheaper than a long block.