SPN 1569 FMI 31 — Engine Protection — Power Derate Active
A general engine-protection derate is active. The ECM has pulled power to protect the engine because another monitored parameter — coolant temp, oil pressure, aftertreatment, or boost — is out of range. SPN 1569/FMI 31 tells you a derate is on; it does not by itself say why.
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
- Aftertreatment fault (DPF/DEF/SCR) commanding a derate
- High coolant temperature or low coolant level
- Low oil pressure protection
- Boost/turbo or intake-air fault the ECM is guarding against
First moves (roadside)
- Read the COMPANION active codes — SPN 1569 alone won't tell you the trigger; the partner code will.
- Check the dash: coolant temp, oil pressure, and DEF/check-engine lamps.
- If gauges are normal, suspect an aftertreatment-driven derate and inspect for DPF/DEF codes.
- Don't keep pushing a derated truck under load — it can escalate to a no-start or engine damage.
Common misdiagnoses
- Treating 1569 as the root cause instead of reading the companion fault that triggered it.
- Assuming it's always emissions — overheating and low oil pressure trigger the same derate flag.
- Clearing the derate without addressing the underlying parameter that's out of range.
FAQ
A general engine-protection derate is active. The ECM has pulled power to protect the engine because another monitored parameter — coolant temp, oil pressure, aftertreatment, or boost — is out of range. SPN 1569/FMI 31 tells you a derate is on; it does not by itself say why.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Aftertreatment fault (DPF/DEF/SCR) commanding a derate. Other possibilities include High coolant temperature or low coolant level; Low oil pressure protection; Boost/turbo or intake-air fault the ECM is guarding against.
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.