CAT Engine 611 Fault Code: Cylinder #6 Injector fault
Also called Cylinder #6 Injector Fault, Injector Cylinder #6 fault
Cylinder #6 Injector fault · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Code 611 (SPN 656 / FMI 11) means the ECM detected an open circuit or a short circuit in the cylinder #6 injector circuit while trying to operate that injector. Because two cylinders share a common wire for their injectors, a fault in that shared wire can affect a second cylinder along with #6. Expect engine misfires and low power while the condition is active. Applies to C10, C12, C15, and C16 engines.
High severity. This code causes engine misfires and low power right away, and it can silently disable the #6 injector while the ECM keeps trying to fire it. It won't strand most machines instantly, but running on a dead or misfiring cylinder risks further engine damage and should be diagnosed as soon as practical, not left for the next scheduled service.
What does CAT Engine error code 611 mean?
Fault code 611 flags a wiring or component problem in the electrical circuit that fires the cylinder #6 injector solenoid. The ECM commands the injector to fire, then checks the circuit's electrical response. If it sees an open circuit, a short to ground, or a short to battery voltage instead of a normal signal, it logs code 611.
This is strictly an electrical circuit fault, not a fuel quality or mechanical timing fault, though mechanical problems in the cylinder can also trigger it. The injector itself may stop operating while the fault is present, which is why the engine misfires and loses power immediately.
Because Caterpillar's injector wiring uses a shared common wire between two cylinders, a fault in that common leg can knock out both cylinders at once rather than just #6. This is an important clue during diagnosis: if two cylinders are misfiring together, suspect the shared common wire before chasing two separate injectors.
Common causes of 611
- Damaged or corroded connectors and/or wiring in the injector circuit
- A problem in the engine wiring harness, including a short in the injector harness or a harness shorted to ground
- A faulty or failed injector solenoid
- A bad or faulty injector that needs replacement
- A mechanical problem in the cylinder itself
- An intermittent electrical problem that comes and goes
- A faulty ECM (less common, but listed as a possible cause)
How to troubleshoot CAT Engine 611: first checks
- Check the injector wiring harness and connectors at cylinder #6 for corrosion, loose pins, chafing, or physical damage before disturbing anything else.
- Trace the shared common wire between cylinder #6 and its paired cylinder. If both cylinders are misfiring together, focus on this common wire rather than assuming two bad injectors.
- With the engine off, check the injector solenoid circuit for open circuits, shorts to ground, or shorts to battery voltage using appropriate test equipment and Caterpillar's wiring diagrams for the specific engine model.
- Inspect the injector itself for signs of mechanical failure if wiring and solenoid checks come back clean.
- Watch for intermittent behavior, wiggle-test connectors and harness routing while monitoring for the fault, since several of the listed causes are intermittent in nature.
- If wiring, solenoid, and injector all check out, consider that the ECM itself may be at fault, but treat this as a last resort after ruling out the wiring and injector.
How the code clears
No separate clearing step is listed. The ECM logs the code automatically and keeps attempting to operate the injector while the underlying wiring, solenoid, injector, or ECM problem is repaired. Once the actual fault (open circuit, short to ground, or short to battery voltage) is corrected, the code should stop being active; verify with a diagnostic scan tool that the code is no longer current after repairs.
Affected models and serial ranges
611 appears in our records across 4 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C10 | Serial range not listed in source records |
| C12 | Serial range not listed in source records |
| C15 | Serial range not listed in source records |
| C16 | Serial range not listed in source records |
Frequently asked questions
What does CAT code 611 mean?
It means the ECM detected an open circuit or short circuit in the wiring for the cylinder #6 injector solenoid while trying to fire that injector. It applies to C10, C12, C15, and C16 engines and corresponds to SPN 656, FMI 11.
Can I keep running the machine with code 611 active?
The ECM will keep trying to operate the injector, but the injector may not fire while the fault is present, causing misfires and low power. Running for extended periods on a dead or misfiring cylinder risks further engine wear, so it should be diagnosed and repaired promptly rather than ignored.
Why is a second cylinder misfiring along with cylinder #6?
Caterpillar's injector wiring uses a shared common wire between certain cylinder pairs. If the fault is in that common wire rather than the individual injector circuit, both cylinders on that shared line can be affected at the same time.
Is code 611 a fuel problem or an electrical problem?
It's an electrical circuit fault: an open circuit, a short to ground, or a short to battery voltage in the injector solenoid circuit. A mechanical problem in the cylinder can also set the code, but the root detection is electrical.
What's the most common cause of a 611 code?
Damaged or corroded wiring and connectors, and problems within the wiring harness, are listed most often across Caterpillar's documented causes for this code, along with faulty solenoids and faulty injectors.
Does code 611 require an ECM replacement?
Rarely. A faulty ECM is listed as a possible cause, but wiring, connectors, the injector solenoid, and the injector itself should all be ruled out first since these are far more common causes.
How do I clear code 611 after repairs?
There's no separate reset procedure listed. Once the wiring, solenoid, or injector issue is fixed, the ECM should stop logging the fault. Confirm with a diagnostic scan tool that the code is no longer active.