SPN 633 FMI 6 — Fuel Injection Control Valve Circuit Current Above Normal
High-current fuel control valve codes are short diagnostics first. Repeat fuse or driver failures when a harness short remains after valve replacement is the most documented pattern — the short source must be identified and repaired before a new valve is installed.
Fault Overview
SPN 633 FMI 6 indicates the fuel injection control valve circuit is drawing current above the normal maximum — a short class fault on the IMV, FCA, or equivalent rail control valve circuit. Shorted coil, harness short to power or ground, oil or fuel bridging a connector, and pinched loom are the primary causes. Repeat fuse or ECM driver failures when a harness short remains after valve replacement is the most documented pattern.
Engine & Platform Coverage
Possible Causes
- 1.Shorted valve coil — internal winding short to case or between windings
- 2.Harness short to power or ground from insulation damage at clamp points
- 3.Oil or fuel bridging at valve connector — contamination creating a conductive path
- 4.Pinched loom near pump assembly or chassis bracket
- 5.Damaged insulation from heat exposure near injection system
Wiring & Circuit Notes
Inspect harness for insulation damage at clamp points near pump assemblies — this is the most common location for shorts in the control valve circuit. Check for oil or fuel contamination at the valve connector that could bridge terminals. Verify harness routing is not pinched against chassis brackets or heat sources.
DVOM Specs & Sensor Tests
Measure coil resistance with valve disconnected — low resistance below OEM minimum supports an internal short. Check harness for shorts to power and ground with valve disconnected. Avoid repeated actuation commands into a shorted circuit — this risks ECM driver damage. Confirm the harness is clean before installing a replacement valve.
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 control valve connector
- 2Measure coil resistance — compare to OEM specification; low resistance indicates internal short
- 3Check harness for shorts to power and ground with valve disconnected
- 4Inspect connector for oil/fuel contamination bridging terminals
- 5Inspect harness at clamp points near pump assembly for insulation damage
- 6Repair harness short before installing replacement valve if harness short is found
- 7Replace valve only after harness is proven clean
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
5 steps locked- 1Disconnect control valve connector
- 2Measure coil resistance — compare to OEM specification; low resistance indicates internal short
- 3Check harness for shorts to power and ground with valve disconnected
- 4Inspect connector for oil/fuel contamination bridging terminals
- 5Inspect harness at clamp points near pump assembly for insulation damage
- 6Repair harness short before installing replacement valve if harness short is found
- 7Replace valve only after harness is proven clean
Unlock full diagnostic steps, DVOM tests, and repair procedures.
Full Diagnostic Access
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Summary
SPN 633 FMI 6 is a short-circuit diagnosis at the fuel control valve. The short source must be identified and repaired before a replacement valve is installed to prevent repeat ECM driver failures.