CAT Engine 511 Fault Code: Cylinder #5 Injector fault
Also called Cylinder #5 Injector Fault, Injector Cylinder #5 fault
Cylinder #5 Injector fault · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 511 (SPN 655 / FMI 11) means the ECM detected an open circuit or a short circuit while trying to operate the cylinder #5 injector. It affects the C10, C12, C15, and C16 engines and typically causes engine misfires and low power. If the problem is in the shared common wire, two cylinders can be affected at once.
High severity. The engine will keep running with the code logged, but a misfiring or dead injector causes low power, rough running, and potential damage to the affected cylinder over time. Diagnose promptly rather than running it indefinitely.
What does CAT Engine error code 511 mean?
Fault code 511 is Caterpillar's code for a Cylinder #5 Injector Fault, identified in electronic service tools as SPN 655 with FMI 11. It applies to the C10, C12, C15, and C16 engine families.
The ECM controls each injector by sending an electrical signal to open its solenoid at the right time. When the ECM tries to fire the cylinder #5 injector, it monitors the circuit for a proper response. If it detects an open circuit, a short to ground, or a short to battery voltage instead of the expected signal, it logs this code.
Because injectors on these engines share a common wire between certain cylinders, a fault in that shared wiring can knock out two injectors at once instead of just one. The ECM keeps trying to operate the injector after the code is logged, but the injector may simply not fire while the fault condition is present, leading to a noticeable misfire and a loss of power.
Common causes of 511
- Damaged or corroded connectors and/or wiring at the injector or in the harness
- A problem within the engine harness itself, including chafing or shorts to ground or battery voltage
- A short in the injector harness or a short in the common wire shared between two cylinders
- A mechanical problem within the cylinder itself
- A faulty or failed injector solenoid
- A faulty or worn-out injector needing replacement
- An intermittent connection issue that comes and goes with vibration or temperature
- A faulty ECM (less common, but listed as a possible cause if all wiring and injector components check out)
How to troubleshoot CAT Engine 511: first checks
- Visually inspect the connectors and wiring harness at cylinder #5's injector for damage, corrosion, or loose pins.
- Check the common wire shared between cylinder #5 and its paired cylinder, since a fault there can cause two injectors to act up simultaneously.
- Test the injector solenoid circuit for open circuits, shorts to ground, or shorts to battery voltage using appropriate electrical diagnostic procedures.
- Inspect the engine harness routing for chafe points, pinched sections, or heat damage near the injector wiring.
- If wiring and connectors check out, test or swap the injector itself to rule out a faulty solenoid or worn injector.
- If the problem persists with no wiring or injector fault found, consider ECM diagnostics as a last step.
How the code clears
No separate clearing step is listed for this code. Once the underlying wiring, connector, solenoid, or injector problem is repaired, the ECM should stop logging the fault on subsequent operation. If the code was caused by an intermittent connection, confirm the repair by monitoring for the code's return during normal operation.
Affected models and serial ranges
511 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 511 mean?
It means the ECM detected an open circuit or a short circuit while trying to operate the cylinder #5 injector on a C10, C12, C15, or C16 engine. It is logged as SPN 655 with FMI 11.
Can I keep driving or working with code 511 active?
The engine will continue running and the ECM will keep trying to fire the injector, but expect misfires and low power. It is best to diagnose and repair the fault soon rather than continuing to operate under load for an extended period.
Why would two cylinders be affected by one injector fault code?
The 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's own wiring, both cylinders sharing that wire can lose injector function at the same time.
What are the most common causes of code 511?
The most frequently listed causes are damaged or corroded wiring and connectors, problems within the engine or injector harness, a faulty injector solenoid, and a worn or failed injector. Mechanical cylinder problems, intermittent connections, and a faulty ECM are also possible but less common.
Will fixing the wiring clear the code automatically?
No separate clearing procedure is listed. Once the wiring, connector, solenoid, or injector issue is repaired, the code should not recur during normal operation.
Does code 511 always mean the injector needs to be replaced?
Not necessarily. Damaged wiring, connectors, or a faulty solenoid are common causes and should be ruled out first. Injector replacement is one of several possible fixes if those checks come back clean.