CAT Engine 111 Fault Code: Cylinder #1 Injector fault
Also called Cylinder #1 Injector Fault, Injector Cylinder #1 fault
Cylinder #1 Injector fault · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT fault code 111, SPN 651 FMI 11, means the ECM detected an open circuit or a short circuit in the cylinder #1 injector circuit while trying to operate that injector. It affects the C10, C12, C15, and C16 engine families. Expect engine misfires and low power while the fault is active.
High severity. This code causes engine misfires and low power, and if the fault is in the shared common wire, two cylinders lose proper injector operation at once. It should be diagnosed as soon as practical, not ignored, though it is not an immediate shutdown emergency by itself.
What does CAT Engine error code 111 mean?
Fault code 111 (SPN 651, FMI 11) is logged when the Electronic Control Module tries to fire the cylinder #1 injector and detects an electrical fault in that circuit: an open circuit, a short to ground, or a short to battery voltage.
Because injectors on these engines share a common wire between certain cylinders, a problem in that common wire can knock out proper operation on two cylinders at once, not just cylinder #1. This is an important detail for diagnosis: if you see two related injector codes together, look hard at the shared wiring before condemning two separate injectors.
The ECM keeps logging the code and keeps trying to operate the injector even after the fault is recorded. While the condition is present, the injector may simply not fire, which is what produces the misfire and power loss symptoms.
Common causes of 111
- Damaged, corroded, or disconnected 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 mechanical problem in the cylinder itself
- A faulty or failing injector solenoid
- An intermittent electrical problem that does not show up constantly
- A faulty injector that needs replacement
- A faulty ECM that needs replacement
How to troubleshoot CAT Engine 111: first checks
- Retrieve and confirm the active or logged code and note whether any other injector codes are present at the same time, since a common-wire fault can affect two cylinders together
- Inspect the injector connectors and wiring harness for cylinder #1 for damage, corrosion, chafing, or loose pins
- Check the injector solenoid circuit for open circuits, shorts to ground, or shorts to battery voltage using appropriate wiring diagrams for the engine model
- Wiggle-test the harness and connectors while monitoring for the fault to reappear, since the problem can be intermittent
- If wiring and connectors check out, test the injector solenoid and injector itself for proper function
- Rule out a mechanical problem within the cylinder before condemning the injector or ECM
How the code clears
No separate clearing step is listed. Once the wiring, connector, solenoid, or injector fault is found and repaired, the code should stop being active on the next key cycle, but confirm by rechecking for the code after repairs. No reset procedure is listed for this code.
Affected models and serial ranges
111 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 fault code 111 mean?
It means the ECM detected an open circuit or a short circuit (to ground or to battery voltage) in the cylinder #1 injector circuit while attempting to operate that injector. This is SPN 651, FMI 11.
Can I keep running the engine with code 111 active?
The ECM will keep trying to operate the injector, but expect engine misfires and low power while the fault is active. It is not listed as an immediate shutdown condition, but you should diagnose and repair it as soon as practical since running on a misfiring cylinder is hard on the engine.
Why would two cylinders be affected by one injector code?
Injectors on these engines share a common wire between certain cylinders. If the fault is in that shared common wire rather than in the individual injector circuit, two cylinders can lose proper injector operation at the same time.
What are the most common causes of code 111?
Damaged or corroded connectors and wiring, a problem in the harness (including shorts to ground), a faulty injector solenoid, a faulty injector, a mechanical problem in the cylinder, or an intermittent electrical fault. In some cases the ECM itself is at fault, but this should be the last thing checked, not the first.
Which CAT engines use fault code 111?
This code applies to the C10, C12, C15, and C16 engine models.
How do I clear code 111 after repair?
No reset procedure is listed for this code. After repairing the wiring, connector, solenoid, or injector, verify the code does not return during normal operation.
Does code 111 mean I need a new injector?
Not necessarily. A faulty injector is one of several possible causes, but damaged wiring, connectors, or a harness short are just as likely and should be ruled out first before replacing the injector or the ECM.