SPN 412 FMI 0 — EGR Temperature Above Normal
High EGR temperature is cooler efficiency and sensing diagnosis. Plugged EGR coolers with progressive overtemp are the most documented pattern. The FSM separates true thermal events from sensor bias before cooler replacement.
Fault Overview
SPN 412 FMI 0 indicates EGR temperature above the calibrated maximum. Failed EGR cooler efficiency, coolant flow restriction to the cooler, sensor bias high, excessive EGR mass, and debris-packed cooling package are the primary causes. Plugged EGR coolers and cooler internal restriction with progressive overtemp are documented patterns. Replacing the EGR cooler for a sensor bias fault is the most documented misdiagnosis pattern.
Engine & Platform Coverage
Symptoms
- •EGR temp high
- •EGR cooler inefficient
- •High EGR gas temperature
- •Derate EGR overtemp
- •Progressive overtemp from plugged cooler
Possible Causes
- 1.Failed EGR cooler efficiency — failed EGR cooler efficiency producing above-normal EGR temperature
- 2.Coolant flow restriction — coolant flow restriction to cooler producing above-normal EGR temperature
- 3.Sensor bias high — EGRT sensor bias high producing false above-normal reading
- 4.Excessive EGR mass — excessive EGR mass producing above-normal temperature
- 5.Debris-packed cooling package — debris-packed cooling package reducing coolant flow to cooler
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
4 steps locked behind Technician Mode- 1Step 1 — Sensor Correlation: Compare EGRT with ECT and exhaust temperatures. An extreme offset between EGRT and related temperatures supports a sensor fault. A sensor bias high producing a false above-normal reading confirms a sensing fault. Confirm sensor circuit integrity before any cooler assessment.
- 2Step 2 — Inspect EGR Cooler Coolant Flow: Inspect EGR cooler coolant flow. Plugged EGR coolers and cooler internal restriction with progressive overtemp are documented patterns. Verify coolant flow to the EGR cooler. A coolant flow restriction to the cooler requires cooling system diagnosis.
- 3Step 3 — Evaluate EGR Valve Command: Evaluate EGR valve command. Excessive EGR mass producing above-normal temperature requires EGR valve command evaluation. Verify the EGR valve is not commanding excessive EGR mass.
- 4Step 4 — Cooling Package Inspection: Inspect the cooling package. A debris-packed cooling package reducing coolant flow to the cooler requires cooling package cleaning. Inspect the radiator, charge air cooler, and cooling package for debris and restriction.
- 5Step 5 — EGR Cooler Service After Evidence: Service or replace the EGR cooler only after confirming thermal evidence. Confirm sensor, coolant flow, and EGR command integrity before any cooler service. An EGR cooler replaced for a sensor bias fault will not resolve the fault.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
3 steps locked- 1Repair EGRT sensor circuit if sensor bias is confirmed.
- 2Repair coolant flow restriction if confirmed.
- 3Address EGR valve command if excessive EGR mass is confirmed.
- 4Clean cooling package if debris restriction is confirmed.
- 5Service or replace EGR cooler only after confirming thermal evidence.
Unlock full diagnostic steps, DVOM tests, and repair procedures.
Full Diagnostic Access
Verification steps, preventative measures, severity guidance, and legacy comparison are available in Technician Mode.
Start Diagnosing This Fault Now
AI Diesel Tech walks you through every evidence gate in the correct order. Choose the plan that fits your shop.
Related Resources
Related Fault Codes
AI Diesel Tech — The Technician's Diagnostic Engine
AI Diesel Tech diagnostic logic is built by an ASE Certified Diesel Technician and engineered for professional shop use. Trusted by technicians nationwide — used in shops, fleets, and training programs.
Summary
High EGR temperature is cooler efficiency and sensing diagnosis. The AI Diesel Tech FSM separates true thermal events from sensor bias before cooler replacement.