SPN 412 FMI 1 — EGR Temperature Below Normal
Below-normal EGR temp is usually sensing or circuit first. Unplugged EGRT after cooler service is the most documented pattern. The FSM enforces sensing proof before cooler path work.
Fault Overview
SPN 412 FMI 1 indicates EGR temperature below the expected minimum. Sensor bias low, open circuit, stuck-open cooler flow in conditions expecting higher temperature, and wiring faults are the primary causes. Unplugged EGRT after cooler service is a documented pattern. Replacing or servicing the EGR cooler for a sensor or circuit fault is the most documented misdiagnosis pattern.
Engine & Platform Coverage
Symptoms
- •EGR temp low
- •EGRT sensor cold
- •EGR cooler overcooling
- •Efficiency monitor issues EGR temp
- •Stuck unrealistically low in operation
Possible Causes
- 1.Sensor bias low — EGRT sensor bias low producing below-normal reading
- 2.Open circuit — open circuit in EGRT sensor harness producing stuck-low reading
- 3.Stuck-open cooler flow — stuck-open cooler flow in conditions expecting higher temperature
- 4.Wiring faults — wiring faults producing below-normal sensor reading
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
3 steps locked behind Technician Mode- 1Step 1 — Ambient Correlation: Correlate the EGRT reading with ambient temperature at cold soak. Cold soak should be near ambient. Stuck unrealistically low in operation suggests a sensor or circuit fault. Unplugged EGRT after cooler service is a documented pattern — always inspect the EGRT connector after any recent cooler service.
- 2Step 2 — Circuit Continuity Check: Check circuit continuity. Open signal conditions and connector corrosion producing below-normal readings are documented causes. Verify continuity through the EGRT sensor circuit. An open circuit confirms a harness or connector fault.
- 3Step 3 — Sensor Resistance Checks: Check sensor resistance against OEM specification. A sensor resistance fault confirms a sensor failure. Compare to OEM specification at the measured temperature.
- 4Step 4 — Evaluate Cooler Control Only After Sensing Proof: Evaluate cooler control only after sensing proof. A true overcooling event with correct sensor readings requires cooler control evaluation. Confirm sensor and circuit integrity before any cooler control diagnosis.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
1 steps locked- 1Repair connector or harness if open circuit is confirmed.
- 2Replace EGRT sensor if failure is confirmed after circuit proof.
- 3Address cooler control if true overcooling is confirmed after sensing proof.
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.
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Summary
Below-normal EGR temp is usually sensing or circuit first. The AI Diesel Tech FSM enforces sensing proof before cooler path work.