SPN 45 FMI 2 — Inlet Air Heater Status Data Erratic
Erratic inlet air heater status is usually an intermittent electrical connection. Prove stability under load and vibration before replacing any component.
Fault Overview
SPN 45 reports inlet air heater status. FMI 2 indicates the status data is erratic, intermittent, or implausible relative to command and other sensors. The ECM detects inconsistency between the commanded state and the reported status, or status that changes unexpectedly during a heater cycle.
Engine & Platform Coverage
Symptoms
- •Inlet air heater status erratic fault active
- •Heater status intermittent during cold-start cycle
- •Cold start performance inconsistent
- •Status does not match commanded state
Possible Causes
- 1.Intermittent connection on status or feedback circuit
- 2.Failing relay contacts creating intermittent current
- 3.Loose heater connection causing intermittent current signature
- 4.Network or reporting glitch
- 5.Temperature sensor correlation failure affecting status rationality
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 — Monitor Heater Status and Command Simultaneously: Use scan tool to monitor heater command and status simultaneously during a cold-start cycle. Document when status deviates from command and under what conditions.
- 2Step 2 — Perform Wiggle Test on Harness and Connectors: With the heater commanded on, wiggle all related connectors and harness sections while monitoring status data. A status dropout during wiggle confirms an intermittent connection.
- 3Step 3 — Measure Voltage and Current Stability Under Load: Monitor voltage at the heater and current draw during the heater cycle. Intermittent drops in voltage or current correspond to status fluctuations.
- 4Step 4 — Check Related Temperature Sensors for Correlation: Verify intake temperature sensor readings are stable and correlate with expected values. A biased or intermittent temperature sensor can affect status rationality checks.
- 5Step 5 — Verify Network Integrity: If status is broadcast on J1939, verify network health and check for other network-related faults that could cause status reporting issues.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
2 steps locked- 1Repair intermittent connection identified by wiggle test.
- 2Replace failing relay with degraded contacts.
- 3Clean and torque heater terminals to eliminate intermittent current.
- 4Replace biased intake temperature sensor if correlation failure is confirmed.
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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Related Resources
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Summary
Erratic inlet air heater status is usually an intermittent electrical connection. Prove stability under load and vibration before replacing any component.