Cylinder 4 Injector - Current Below Normal / Open Circuit
What does CAT-INJ4-FMI5 mean?
The CAT-INJ4-FMI5 (Caterpillar) diesel fault code means: Cylinder 4 Injector - Current Below Normal / Open Circuit. This is a serious severity code.
Common Symptoms
- Check Engine Light with rough idle
- Dead cylinder / misfire on affected cylinder
- Power loss and black/white smoke
- Engine derate
Probable Causes (Ranked by Likelihood)
- Injector solenoid coil open Very Likely
- Open wire from ECM to injector Likely
- Connector pin issue at valve cover pass-through Likely
Step-by-Step Diagnostic Procedure
With CAT ET, run cylinder cutout test; the affected cylinder will not change RPM.
Remove valve cover; inspect injector wiring for chafe, disconnected pins, or corrosion.
Ohm the injector solenoid per CAT spec (typically under 1 ohm). Open reading confirms coil failure.
Replace injector if coil is open; repair harness if wire is open.
Frequently Asked Questions
What does CAT code INJ4-FMI5 mean?
CAT code INJ4-FMI5 (Cylinder 4 Injector - Current Below Normal / Open Circuit) is a serious-severity fault on Caterpillar on-highway diesel engines. This code flags cylinder 4 injector fault. CAT on-highway engines use HEUI (hydraulically actuated) injection pre-2007 and common rail post-2007. Confirm with CAT ET cylinder cutout test before replacing a $500-$800 injector. Diagnose with CAT ET (Electronic Technician) software.
Can I drive my truck with CAT code INJ4-FMI5?
Short distances may be acceptable, but running long with this fault risks progressive damage or forced derate. Address promptly.
How much does it cost to fix CAT INJ4-FMI5?
Typical repair is $400-$1800. Sensor / wiring fixes fall at the low end; injector, HEUI pump, turbo, or aftertreatment work falls at the high end. CAT dealer labor often requires CAT ET for calibration and parameter programming.