Cylinder 3 Injector - Current Below Normal / Open Circuit
The CAT-INJ3-FMI5 (Caterpillar) diesel fault code means: Cylinder 3 Injector - Current Below Normal / Open Circuit. This is a serious severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- advanced
- Estimated cost
- $400-$1800
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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
Frequently Asked Questions
What does CAT code INJ3-FMI5 mean?
CAT code INJ3-FMI5 (Cylinder 3 Injector - Current Below Normal / Open Circuit) is a serious-severity fault on Caterpillar on-highway diesel engines. This code flags cylinder 3 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 INJ3-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 INJ3-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
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.
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)
Commonly Affected Vehicles
- 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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