Code Details
| Display code | SPN 412 FMI 0 |
|---|---|
| SPN | 412 |
| FMI | 0 |
| OEM code | None listed |
| Manufacturer | Detroit Diesel |
| System | Engine �?EGR system |
| Component | EGR cooler / EGR temperature sensor |
| Source address | Unknown or not applicable |
| Severity | medium |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-11 |
Plain-English Meaning
The DD15 EGR cooler reduces the temperature of recirculated exhaust gases before they re-enter the engine's intake system. When post-cooler EGR temperature is too high, the cooler is not cooling the gases adequately �?typically from a bypass valve fault, restricted coolant flow, or a degraded cooler core. This affects combustion quality and may accelerate intake system wear. On Freightliner Cascadia and Western Star trucks with the DD15, EGR cooler failures are a known service issue on high-mileage units. A cracked EGR cooler allows coolant to enter the exhaust stream, which contaminates the DPF and can mask itself as an exhaust temperature sensor fault before the underlying EGR cooler failure is identified. DiagnosticLink monitors EGR cooler outlet temperature and can detect the characteristic temperature irregularity caused by coolant entering the exhaust. Checking coolant level regularly and watching for a steadily dropping coolant level without an external leak is the most reliable field indicator of an EGR cooler leak.
SPN 412 FMI 0 is EGR Temperature above normal. On Detroit DD15 MCM2.0, DiagnosticLink monitors EGR cooler inlet and outlet temperatures, coolant temperature, and the EGR bypass valve position. A stuck-open EGR bypass valve is a known cause of high post-cooler EGR temperature on the DD15 �?the bypass routes uncooled exhaust directly around the cooler.
Common Symptoms
- Check engine lamp active
- Higher intake temperatures contributing to elevated combustion temperatures
- Possible concurrent coolant temperature rise if the EGR cooler is adding heat to the coolant circuit due to partial internal failure
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- EGR cooler bypass valve stuck in open or partially open position
- Restricted coolant flow through the EGR cooler
- EGR cooler core degradation reducing heat transfer
- EGR temperature sensor drift
First Checks
- Connect DiagnosticLink and check EGR bypass valve position and command vs. actual
- Monitor EGR inlet and outlet temperatures to quantify the temperature drop across the cooler
- Check coolant flow to the EGR cooler circuit
- Look for companion codes indicating EGR bypass valve control fault
- Monitor EGR cooler inlet and outlet temperature differential in DiagnosticLink
- Check coolant level over several operating cycles for a slow, unexplained decrease without visible external leaks
Can I Keep Driving?
Typically driveable. If coolant temperature is also rising, investigate more urgently for potential EGR cooler internal failure.
Related Codes
Related Lookup Pages
Sources
- Detroit Diesel Service and Diagnostic Resources — Public Reference Detroit Diesel (Daimler Truck North America) · oem · accessed 2026-06-11 · confidence medium
Source: Detroit Diesel (Daimler Truck North America), Detroit Diesel Service and Diagnostic Resources — Public Reference. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - DiagnosticLink Detroit Diesel Corporation · oem · accessed 2026-05-05 · confidence medium
Source: Detroit Diesel Corporation, DiagnosticLink. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - SAE J1939 Standards Collection SAE International · official · accessed 2026-05-05 · confidence medium
Source: SAE International, SAE J1939 Standards Collection. This page paraphrases factual fields only and is not a substitute for the original document.
Open source
FAQ
Is the EGR bypass valve on the Detroit DD15 a common failure point?
The EGR bypass valve on the DD15 is identified as a wear item that can stick in the open or partially open position after extended operation. Carbon buildup around the valve seat and actuator mechanism contributes to sticking. DiagnosticLink can command the valve to open and close to confirm responsiveness and identify if it is stuck.
Can a high EGR temperature cause NOx spikes on the Detroit DD15?
Yes. EGR cooling is a critical part of the NOx control strategy on the DD15. When EGR gases enter the intake at higher-than-intended temperatures, they are less effective at reducing peak combustion temperatures, which can cause engine-out NOx to increase. This may contribute to SCR loading and efficiency faults over time.
How do I know if the DD15 EGR cooler needs replacement vs. just the bypass valve?
If DiagnosticLink shows the bypass valve is responding correctly to commands (opening and closing on demand) but EGR outlet temperature is still above normal, the cooler core performance is degraded. If the bypass valve is confirmed stuck open, repairing the valve may restore adequate cooling without replacing the cooler. A temperature differential test across the cooler with the bypass confirmed closed provides the clearest data for this decision.