CAT Engine 26066 Fault Code: Cylinder #3 Injector Actuator #2:Current Above Normal
Also called Cylinder #3 Injector Actuator #2 - Current Above Normal, Cylinder #3 Injector Actuator #2 : Current Above Normal
Cylinder #3 Injector Actuator #2:Current Above Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 26066, SPN 3661 FMI 6, means the ECM detected current above normal on the #2 solenoid circuit of the #3 cylinder's electronic unit injector. This points to a short circuit or wiring problem in that injector's actuator #2 circuit on C13, C15, C18, C27, and C32 engines.
High severity. The ECM disables the affected solenoid circuit to prevent damage from the high current flow but keeps periodically retrying to fire the injector. This causes rough running, misfire on cylinder #3, and possible power loss until the wiring or component issue is corrected.
What does CAT Engine error code 26066 mean?
CAT C13, C15, C18, C27, and C32 engines use Electronic Unit Injectors (EUI). Each injector has two solenoids, and the ECM sends 105 volt pulses to each solenoid at the correct time and duration for the current engine load and speed.
The ECM continuously monitors current flow through each solenoid circuit. Code 26066 sets when the ECM detects current above normal (FMI 6) on the actuator #2 circuit for the #3 cylinder injector. When this happens, the ECM disables that solenoid circuit to prevent damage from the excess current, then periodically attempts to re-fire the injector. If the short circuit condition persists, this disable-and-retry cycle repeats until the underlying problem is fixed.
This is different from a low-current, open-circuit fault. High current above normal generally points to a short somewhere in the actuator #2 wiring, connector, or the injector solenoid itself, rather than a broken wire.
Common causes of 26066
- Damaged, corroded, or shorted connectors or wiring in the actuator #2 circuit for the #3 cylinder injector
- A short or fault in the wiring harness between the ECM and the injector connector, including the section running under or near the valve cover base
- An electronic problem within the injector itself, such as a failed solenoid
- An intermittent fault that only appears under engine vibration or heavy load, often after the engine reaches normal operating temperature
- A faulty ECM (considered only after wiring and injector have been ruled out)
How to troubleshoot CAT Engine 26066: first checks
- Run the engine to normal operating temperature before testing since these faults often only show up warmed up and under vibration or load, matching the conditions when the problem actually occurs
- Inspect the connectors and wiring for the #3 cylinder injector's actuator #2 circuit for corrosion, chafing, pinched wires, or loose pins, paying close attention to sections near the valve cover base and under the valve cover
- Check the wiring harness between the ECM and the injector connector for continuity and confirm there is no open or shorted circuit along that run
- Wiggle-test the harness and connectors while the engine is running or under load to try to reproduce an intermittent short, since vibration-related faults may not show up at idle or with the engine cold
- If wiring and connectors check out, test the injector solenoid itself for a short before considering it a bad injector
- Only after wiring, connectors, harness, and injector are all confirmed good should the ECM itself be suspected
How the code clears
No separate clearing step is listed. The code should clear once the shorted wiring, connector, or injector solenoid is repaired or replaced and the ECM no longer detects current above normal on the circuit. Because the ECM keeps periodically retrying to fire the injector, expect the fault to reappear on the next drive cycle if the underlying short has not actually been fixed.
Affected models and serial ranges
26066 appears in our records across 5 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C13 | Serial range not listed in source records |
| C15 | Serial range not listed in source records |
| C18 | Serial range not listed in source records |
| C27 | Serial range not listed in source records |
| C32 | Serial range not listed in source records |
Frequently asked questions
What does CAT code 26066 mean?
It means the ECM detected current above normal, an electrical short condition, on the actuator #2 solenoid circuit of the #3 cylinder's electronic unit injector. SPN 3661 identifies the circuit and FMI 6 identifies the current-above-normal failure mode.
Which CAT engines can show fault 26066?
This code applies to the C13, C15, C18, C27, and C32 engine platforms that use Electronic Unit Injectors with dual solenoids controlled by the ECM.
Is it safe to keep running the engine with this code active?
The ECM will disable the affected solenoid circuit and keep retrying to fire the injector, which usually causes a rough-running or misfiring cylinder #3. It is not an immediate stop-the-engine emergency, but running for extended periods with a misfiring cylinder can cause added wear and should be diagnosed soon rather than ignored.
Why does this fault only show up sometimes?
Injector solenoid wiring and connector problems often only appear once the engine is warmed up and under vibration from heavy load. A connector or wire that tests fine cold and at idle can short out once the engine heats up and starts shaking under load.
Could this be a bad ECM instead of wiring?
It is possible, but ECM failure is the least common cause. Wiring, connectors, the harness between the ECM and the injector, and the injector solenoid itself should all be inspected and ruled out first.
Will replacing the injector automatically fix code 26066?
Not necessarily. Since the possible causes include wiring, connectors, harness faults, and the injector solenoid, replacing the injector without checking the wiring first can leave the actual short in place and cause the new injector to fail the same way.