SPN 174 FMI 2 — Fuel Temperature Data Erratic
Erratic fuel temperature is typically sensor or harness integrity. Intermittent derate logic from unstable fuel temp inputs on some strategies is the most documented pattern. The FSM enforces intermittent process control before fueling system teardown.
Fault Overview
SPN 174 FMI 2 indicates fuel temperature signal unstable or implausible. Failing sensor, connector fretting, harness heat damage, poor ground, and intermittent open are the primary causes. Intermittent derate logic from unstable fuel temp inputs on some strategies is a documented pattern. Chasing fueling system components for a bad fuel temperature sensor is the most documented misdiagnosis pattern.
Engine & Platform Coverage
Symptoms
- •Fuel temp sensor intermittent
- •Erratic fuel temperature
- •Fuel temperature jumping
- •Intermittent derate from fuel temp
- •Power loss in heat from fuel temp fault
Possible Causes
- 1.Failing sensor — failing fuel temperature sensor producing unstable readings
- 2.Connector fretting — connector fretting producing intermittent signal
- 3.Harness heat damage — harness heat damage producing intermittent open
- 4.Poor ground — poor ground producing unstable sensor readings
- 5.Intermittent open — intermittent open in sensor circuit
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 — Visual Connector Inspection: Inspect the sensor pigtail near filters and rails. Inspect for oil and fuel contamination of connectors. Connector fretting and oil or fuel contamination producing intermittent signals are documented causes. Confirm the connector is clean and fully seated.
- 2Step 2 — Wiggle Test: Perform a wiggle test on the sensor connector and harness. Monitor the fuel temperature PID while wiggling the harness. A PID dropout during the wiggle test confirms a harness intermittent. Compare the reading to ambient and operating expectations.
- 3Step 3 — Resistance and Continuity Check: Check resistance and continuity. Verify sensor resistance against OEM specification. Verify continuity through the sensor circuit. A resistance or continuity fault confirms a sensor or harness fault.
- 4Step 4 — Replace Sensor After Proof: Replace the sensor after proof of sensor failure. Confirm the harness and connector are clean before sensor replacement. A sensor replaced without proof may replace a good sensor into a harness fault.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
1 steps locked- 1Repair harness if intermittent is confirmed.
- 2Service connector if fretting or contamination is confirmed.
- 3Replace sensor if failure is confirmed after circuit 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.
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.
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Summary
Erratic fuel temperature is typically sensor or harness integrity. The AI Diesel Tech FSM enforces intermittent process control before fueling system teardown.