SPN 108 FMI 2 — Barometric Pressure Data Erratic
Erratic BARO is sensor and harness integrity first. Intermittent power and boost complaints from unstable BARO input — with the ECM replaced instead of the sensor — is the most documented misdiagnosis.
Fault Overview
SPN 108 FMI 2 indicates barometric pressure data is unstable or implausible. Failing BARO sensor, intermittent harness, poor reference or ground, moisture intrusion, and internal ECM BARO instability (less common) are the primary causes.
Engine & Platform Coverage
Possible Causes
- 1.Failing BARO sensor with intermittent output
- 2.Intermittent harness at sensor connector or related ground points
- 3.Poor reference stability at BARO sensor connector
- 4.Moisture intrusion at sensor connector producing intermittent bridging
- 5.Internal ECM BARO instability — less common, requires all external proof first
Wiring & Circuit Notes
Graph BARO stability at KOEO parked. Atmospheric pressure does not jump wildly — abrupt swings are electrical or sensor. Wiggle test at sensor connector and related ground points while monitoring BARO PID.
DVOM Specs & Sensor Tests
Graph BARO stability at KOEO parked — atmosphere does not jump. Abrupt swings are electrical or sensor. Wiggle test at sensor connector and ground points while monitoring PID. Check reference and ground stability. Replace BARO sensor after proof. ECM path only if OEM indicates internal BARO and all external proof is perfect.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
5 steps locked behind Technician Mode- 1Graph BARO stability at KOEO parked
- 2Abrupt swings confirm electrical or sensor fault
- 3Wiggle test at sensor connector and ground points while monitoring PID
- 4Check reference and ground stability at sensor connector
- 5Replace BARO sensor after proof
- 6ECM path only if OEM indicates internal BARO and all external proof is perfect
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
4 steps locked- 1Graph BARO stability at KOEO parked
- 2Abrupt swings confirm electrical or sensor fault
- 3Wiggle test at sensor connector and ground points while monitoring PID
- 4Check reference and ground stability at sensor connector
- 5Replace BARO sensor after proof
- 6ECM path only if OEM indicates internal BARO and all external proof is perfect
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
SPN 108 FMI 2 is sensor and harness integrity first. Stability graphing and external proof are required before any ECM conclusions.