CAT Engine 311 Fault Code: Cylinder #3 Injector fault
Also called Cylinder #3 Injector Fault, Injector Cylinder #3 fault
Cylinder #3 Injector fault · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 311 means the ECM detected an open or short circuit while trying to operate the cylinder #3 injector. It logs as SPN 653 / FMI 11 on C10, C12, C15, and C16 engines. Expect engine misfires and low power while the fault is active, and check the shared common wire since a wiring fault there can knock out two cylinders at once.
High severity. The engine will keep running but with misfires and low power, and a common-wire fault can disable two injectors at once. Not an immediate shutdown risk, but it should be diagnosed promptly to avoid further misfire damage or a stall under load.
What does CAT Engine error code 311 mean?
CAT fault code 311 is set when the Electronic Control Module tries to fire the cylinder #3 injector and detects an electrical fault in that circuit rather than a normal response. The ECM can detect three specific fault conditions: an open circuit in the injector solenoid circuit, a short to ground, or a short to battery voltage.
This is strictly an electrical detection fault, not necessarily a fuel or mechanical problem, though mechanical issues in the cylinder can also trigger it. The ECM logs the code and keeps trying to operate the injector, but the injector may not fire correctly while the fault is present.
Because injectors on these engines share a common wire, a fault in that shared wiring can affect two cylinders at the same time, not just cylinder #3. This is an important clue when diagnosing: if you see two related injector codes together, look at the common wire first before replacing parts.
What triggers a CAT Engine 311 code?
The ECM sets this code when it attempts to operate the cylinder #3 injector and detects one of three conditions: an open circuit in the injector solenoid circuit, a short circuit to ground, or a short circuit to battery voltage. No specific voltage, time, or temperature thresholds are listed for triggering this code.
Common causes of 311
- Damaged or corroded connectors and/or wiring at the injector or in the harness
- A problem in the engine wiring harness, including a short in the injector harness or a harness shorted to ground
- A fault in the injector solenoid itself
- A faulty or worn-out injector that needs replacement
- A mechanical problem within the cylinder itself
- An intermittent electrical problem that may not show up during every test
- A faulty ECM, though this is listed as a less common cause and should be ruled out last
How to troubleshoot CAT Engine 311: first checks
- Retrieve and confirm the active/logged code, and check for a paired injector code on another cylinder, since a shared common wire fault can affect two cylinders together
- Visually inspect the connectors and wiring at the cylinder #3 injector for corrosion, damage, chafing, or loose pins
- Trace the injector harness back toward the ECM, checking for shorts to ground, shorts to battery voltage, or open circuits, paying close attention to the common wire shared between injectors
- Check for engine misfires and low power symptoms to confirm the injector is not firing correctly while the code is active
- Test the injector solenoid resistance and circuit continuity per the wiring diagram to isolate whether the fault is in the wiring, the solenoid, or the injector itself
- If wiring and solenoid test good, inspect for a mechanical problem in the cylinder before condemning the injector or the ECM
How the code clears
No separate clearing step is listed for this code. The ECM continues logging the code and attempting to operate the injector as long as the fault condition is present. Once the underlying wiring, solenoid, or injector problem is repaired and the circuit tests correctly, the code should stop being active on the next key cycle or diagnostic check. Always verify the repair with a scan tool to confirm the code clears and does not return.
Affected models and serial ranges
311 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 311 mean?
It means the ECM detected an open circuit or a short circuit (to ground or to battery voltage) while trying to operate the cylinder #3 injector. It logs as SPN 653 with FMI 11 on C10, C12, C15, and C16 engines.
Will code 311 cause the engine to shut down?
No shutdown is described for this code. The engine keeps running, but you can expect engine misfires and low power while the fault is active, since the affected injector may not fire correctly.
Can this fault affect more than one cylinder?
Yes. Injectors on these engines share a common wire. If the root cause is a problem in that shared wire, two cylinders can be affected at the same time, not just cylinder #3. Always check for a paired code on another cylinder.
What are the most common causes of code 311?
The most frequently listed causes are damaged or corroded wiring and connectors, a problem in the engine harness, a faulty injector solenoid, or a faulty injector itself. Mechanical problems in the cylinder, intermittent electrical faults, and a faulty ECM are also possible but less common.
Do I need to replace the injector to fix code 311?
Not necessarily. Start by inspecting wiring, connectors, and the injector solenoid circuit. Many cases trace back to damaged wiring or connectors rather than a bad injector. Replace the injector only after wiring and solenoid checks come back clean.
How do I know if the problem is the ECM instead of the injector or wiring?
A faulty ECM is listed as a possible cause, but it should be the last thing you check. Rule out damaged wiring, connectors, the injector solenoid, and the injector itself first, since these are far more commonly the actual cause.
Does code 311 clear itself once repaired?
No specific clearing procedure is documented. Once the wiring, solenoid, or injector issue is properly repaired and the circuit tests normal, the code should stop being active. Confirm with a scan tool that it does not return after the repair.