SPN 412 FMI 0 — EGR Temperature — Too High
EGR gas temperature is above the high limit. Sustained high EGR temps point to an EGR cooler or coolant-flow problem and can damage the cooler/engine, so the ECM warns and derates.
Your SPN/FMI rides along, so nearby mechanics see the fault before they quote you.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Plugged or failing EGR cooler (reduced heat transfer)
- Low coolant level or poor coolant flow to the cooler
- Stuck-open EGR valve flowing too much hot gas
- Temperature sensor fault reading high (verify first)
First moves (roadside)
- Check coolant level and look for leaks — low coolant starves the EGR cooler.
- Watch EGR temp behavior under load to see if it's real or a sensor fault.
- Look for companion coolant-temp or EGR-position codes.
- Reduce load and get to a safe stop if temps keep climbing.
Common misdiagnoses
- Replacing the temp sensor when the EGR cooler was actually failing.
- Missing a low-coolant condition behind the high temps.
- Ignoring a stuck-open EGR valve as the heat source.
FAQ
EGR gas temperature is above the high limit. Sustained high EGR temps point to an EGR cooler or coolant-flow problem and can damage the cooler/engine, so the ECM warns and derates.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Plugged or failing EGR cooler (reduced heat transfer). Other possibilities include Low coolant level or poor coolant flow to the cooler; Stuck-open EGR valve flowing too much hot gas; Temperature sensor fault reading high (verify first).
Power derate likely — plan to stop soon. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Find a mechanic or related guides
General diagnostic guidance for heavy-duty diesel engines (Cummins, Detroit, PACCAR, Volvo, Mack). Not a substitute for a scan-tool diagnosis on your specific truck.