SPN 102 FMI 4 — Intake Manifold Pressure Circuit Voltage Below Normal
MAP circuit low-voltage codes require shared 5V bus awareness — one shorted sensor on the same reference supply can collapse the bus and create multiple simultaneous sensor codes. Disconnect isolation identifies the short source before any sensor is replaced.
Fault Overview
SPN 102 FMI 4 indicates the intake manifold pressure sensor circuit voltage is below the normal minimum — a short circuit or low-signal class fault. Signal short to ground, failed sensor, crushed harness, water intrusion, and a shorted shared 5V companion sensor collapsing the bus are the primary causes. One shorted sensor collapsing the reference and creating multiple codes is the most documented pattern.
Engine & Platform Coverage
Possible Causes
- 1.Signal wire short to ground from pinched or crushed harness
- 2.Failed MAP sensor with internal short to ground
- 3.Water intrusion at connector bridging signal to ground
- 4.Shorted companion sensor on the same 5V reference supply collapsing the bus
- 5.Insulation damage at pinch points near intake manifold brackets
Wiring & Circuit Notes
Check 5V bus voltage with all sensors connected — a collapsed bus (significantly below 5V) indicates a short on the shared reference. Disconnect sensors one at a time to identify which sensor is pulling the bus down. Inspect harness for pinch points near intake manifold brackets and clamps.
DVOM Specs & Sensor Tests
Measure 5V bus voltage with all sensors connected. If bus is collapsed, disconnect sensors one at a time and recheck bus voltage after each disconnection — the bus voltage will recover when the shorted sensor is disconnected. With MAP sensor disconnected, check signal wire for short to ground independently.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
5 steps locked behind Technician Mode- 1Measure 5V reference bus voltage with all sensors connected
- 2If bus is collapsed, disconnect sensors one at a time to identify the short source
- 3With MAP sensor disconnected, check signal wire for short to ground
- 4Inspect harness for pinch points near intake manifold brackets
- 5Repair harness short or replace shorted sensor
- 6Verify bus voltage recovers after repair before returning to service
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
4 steps locked- 1Measure 5V reference bus voltage with all sensors connected
- 2If bus is collapsed, disconnect sensors one at a time to identify the short source
- 3With MAP sensor disconnected, check signal wire for short to ground
- 4Inspect harness for pinch points near intake manifold brackets
- 5Repair harness short or replace shorted sensor
- 6Verify bus voltage recovers after repair before returning to service
Unlock full diagnostic steps, DVOM tests, and repair procedures.
Full Diagnostic Access
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Summary
SPN 102 FMI 4 requires 5V bus health assessment and disconnect isolation to identify the short source — which may be a companion sensor rather than the MAP sensor itself.