Cylinder 4 Injector - Current Below Normal / Open Circuit
The CAT-INJ4-FMI5 (Caterpillar) diesel fault code means: Cylinder 4 Injector - Current Below Normal / Open Circuit. This is a serious severity code.
Unverified. We could not confirm this code's definition against freely available manufacturer documentation, so treat the meaning, severity and fix guidance on this page as unconfirmed. Check it against the manufacturer's service information for your exact model and serial range before acting on it. This page is kept out of search engines for that reason, and we are working through this family manual by manual.
- Keep driving?
- Short distances only
- DIY difficulty
- advanced
- Estimated cost
- $400-$1800
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View pilot availability →What Are the Symptoms of CAT-INJ4-FMI5?
- Check Engine Light with rough idle
- Dead cylinder / misfire on affected cylinder
- Power loss and black/white smoke
- Engine derate
What Causes CAT-INJ4-FMI5? (Most Likely First)
- Injector solenoid coil open Very Likely
- Open wire from ECM to injector Likely
- Connector pin issue at valve cover pass-through Likely
Can I Still Drive with CAT-INJ4-FMI5?
Short distances only. CAT-INJ4-FMI5 is rated serious severity. Keep trips short and get it diagnosed soon rather than waiting for symptoms to worsen.
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.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose CAT-INJ4-FMI5?
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.
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J1939-73Application Layer: Diagnostics (defines the SPN/FMI fault-identifier framework)
Which Vehicles Commonly Get CAT-INJ4-FMI5?
- Kenworth T800 with CAT C15
- Kenworth W900 with CAT C15
- Kenworth T2000 with CAT C15
- Peterbilt 379 with CAT C15
- Peterbilt 389 with CAT C15
- Peterbilt 386 with CAT C15
- Peterbilt 387 with CAT C15
- Freightliner Classic XL with CAT C15
- International 9200i with CAT C15
- International 9400i with CAT C15
- Western Star 4900 with CAT C15
- Western Star 5900 with CAT C15
- Kenworth T800 with CAT C13
- Kenworth T660 with CAT C13
- Peterbilt 386 with CAT C13
- Peterbilt 387 with CAT C13
- Freightliner Columbia with CAT C13
- International 9200i with CAT C13
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