SPN 652 FMI 4 — Injector Cylinder 2 Circuit Voltage Below Normal
Cylinder 2 injector short codes need short isolation before another injector is installed. Oil intrusion creating intermittent high-current faults is the most documented cause.
Fault Overview
SPN 652 FMI 4 indicates the cylinder 2 injector circuit voltage is below the valid minimum — a short circuit or low-signal class fault. Internal injector short, harness short, oil bridging, and pinched loom are the primary causes.
Engine & Platform Coverage
Possible Causes
- 1.Internal cylinder 2 injector short to ground
- 2.Harness short from valve-cover edge chafe
- 3.Oil-filled connector bridging terminals at cylinder 2
- 4.Pinched loom after injector or valve-cover service
- 5.Oil intrusion creating intermittent high-current faults
Wiring & Circuit Notes
Inspect valve-cover edge chafe and oil-filled connectors — these are the highest-probability short locations for cylinder 2 injector circuits. Avoid repeated actuation into a short.
DVOM Specs & Sensor Tests
Disconnect the cylinder 2 injector and measure resistance — below OEM minimum supports internal short. Check short-to-power and short-to-ground with injector disconnected. If short clears with injector disconnected, the injector is internally shorted. If short persists, inspect harness at valve-cover edge and bracket chafe points. Repair circuit before installing a new injector if harness is at fault.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
6 steps locked behind Technician Mode- 1Disconnect cylinder 2 injector connector
- 2Measure injector resistance — below OEM minimum supports internal short
- 3Check short-to-power and short-to-ground with injector disconnected
- 4If short clears with injector disconnected — replace injector
- 5If short persists — inspect harness at valve-cover edge and bracket chafe points
- 6Repair harness short before installing new injector
- 7Code injector if required by OEM procedure
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
5 steps locked- 1Disconnect cylinder 2 injector connector
- 2Measure injector resistance — below OEM minimum supports internal short
- 3Check short-to-power and short-to-ground with injector disconnected
- 4If short clears with injector disconnected — replace injector
- 5If short persists — inspect harness at valve-cover edge and bracket chafe points
- 6Repair harness short before installing new injector
- 7Code injector if required by OEM procedure
Unlock full diagnostic steps, DVOM tests, and repair procedures.
Full Diagnostic Access
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Summary
SPN 652 FMI 4 is short diagnostics first. Disconnect isolation and harness short checks are required before injector condemnation.