SPN 1112 FMI 6 — Engine Compression Brake Output Circuit Current Above Normal
Overcurrent on the compression brake circuit is a shorted solenoid or load-side short. Isolate by resistance and disconnection.
Fault Overview
FMI 6 sets when current on the compression brake output exceeds the calibrated high limit, indicating a shorted solenoid or short-to-ground on the load side of the driver.
Engine & Platform Coverage
Symptoms
- •Jake brake overcurrent
- •Compression brake short
- •Engine brake high current
- •Solenoid shorted
Possible Causes
- 1.Shorted solenoid coil
- 2.Control or power wire shorted to ground after the driver
- 3.Incorrect low-resistance aftermarket solenoid
- 4.Harness damage creating short
- 5.ECM current-sense fault (rare)
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
5 steps locked behind Technician Mode- 1Step 1 — Measure Solenoid Resistance: Measure solenoid resistance. A reading near 0 Ω indicates an internal short. Compare to OEM specification.
- 2Step 2 — Command Circuit with Solenoid Disconnected: Command the brake with the solenoid disconnected and confirm current drops to near zero. If current remains high, the short is in the harness, not the solenoid.
- 3Step 3 — Inspect Wiring for Short to Ground: Inspect the load-side wiring for pinched wires, melted insulation, or contact with grounded surfaces.
- 4Step 4 — Verify Correct Solenoid Part Number and Resistance: Confirm the installed solenoid matches the OEM part number and resistance specification. Incorrect aftermarket solenoids with wrong coil resistance cause repeated overcurrent faults.
- 5Step 5 — Check Multiple Solenoids on Shared Driver: If multiple solenoids share a driver, disconnect them one at a time to isolate the shorted unit.
- 6Step 6 — Confirm Fuse and Driver Protection Status: Check fuse and driver protection status. Repeated overcurrent events may have damaged the driver or blown protection.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Repair Steps
1 steps locked- 1Replace shorted solenoid with OEM-spec unit (verify resistance).
- 2Repair shorted harness.
- 3Replace damaged connector.
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.
Start Diagnosing This Fault Now
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Summary
Overcurrent on the compression brake circuit is a shorted solenoid or load-side short. Isolate by resistance and disconnection.