Cylinder 5 Injector - Mechanical System Not Responding
What does CAT-INJ5-FMI7 mean?
The CAT-INJ5-FMI7 (Caterpillar) diesel fault code means: Cylinder 5 Injector - Mechanical System Not Responding. This is a moderate severity code.
Common Symptoms
- Rough idle or surging on the affected cylinder
- White smoke or fuel knock
- Power loss; knocking at idle
- ECM flags mechanical injector response
Probable Causes (Ranked by Likelihood)
- Injector internally fouled, stuck, or seized Very Likely
- Low HEUI oil pressure (pre-2007 HEUI engines) Likely
- Low common rail fuel pressure (post-2007 CR engines) Likely
- Injector cup / O-ring failure Possible
Step-by-Step Diagnostic Procedure
Run cylinder cutout on CAT ET to confirm contribution loss on affected cylinder.
Check injection actuation pressure (HEUI engines) or rail pressure (CR engines).
Swap injector to adjacent cylinder; if the fault moves, the injector is mechanically bad.
Replace injector and update trim code via CAT ET.
Frequently Asked Questions
What does CAT code INJ5-FMI7 mean?
CAT code INJ5-FMI7 (Cylinder 5 Injector - Mechanical System Not Responding) is a moderate-severity fault on Caterpillar on-highway diesel engines. This code flags cylinder 5 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 INJ5-FMI7?
No. This fault can trigger engine protect mode, derate, or cause further damage. Park and diagnose before operating.
How much does it cost to fix CAT INJ5-FMI7?
Typical repair is $600-$2800. 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.