CAT Engine 26125 Fault Code: Cylinder #6 Injector Actuator #2:Current Below Normal
Also called Cylinder #6 Injector Actuator #2 - Current Below Normal, Cylinder #6 Injector Actuator #2 : Current Below Normal
Cylinder #6 Injector Actuator #2:Current Below Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 26125 (SPN 3664, FMI 5) means the ECM detected low current flow in the #2 solenoid circuit of the Cylinder #6 injector on C13, C15, C18, C27, and C32 engines. The ECM keeps trying to fire the injector when this happens, but the cylinder may misfire or run rough until the wiring, connector, or injector fault is fixed.
Medium severity. The engine will typically keep running because the ECM keeps attempting to fire the injector, but a persistent low-current fault on one injector solenoid causes rough running, power loss, and possible long-term wear on the injector or ECM driver circuit if left unaddressed. Diagnose within the shift rather than ignoring it.
What does CAT Engine error code 26125 mean?
CAT engines with Electronic Unit Injectors (EUI) use two solenoids per injector, and the ECM fires each one with 105 volt pulses timed and sized for the current engine load and speed. Code 26125 is specific to Cylinder #6, Injector Actuator #2, and it sets when the ECM measures current through that solenoid's circuit and finds it below the expected level.
When current is low, the ECM keeps trying to fire the injector rather than shutting the circuit down, which is different from a high-current short condition where the ECM disables the circuit to prevent damage. A below-normal current reading usually points to a wiring, connector, or component issue in that solenoid's circuit rather than a full electrical short.
Because injector solenoid problems often only show up once the engine is warm and under vibration from load, a wiring or connector fault that looks fine at idle in the shop can still be the root cause. That is why diagnostic procedures call for testing at normal operating temperature and paying close attention to wiring and connectors during the check.
Common causes of 26125
- Damaged, corroded, or loose connectors or wiring in the Cylinder #6, Injector Actuator #2 circuit
- An open or high-resistance circuit in the harness between the ECM and the injector connector
- A fault in the harness between the ECM and the valve cover base, or in the harness under the valve cover
- An intermittent electronic problem with the injector solenoid itself
- A bad or worn-out injector requiring replacement
- A faulty ECM (less common, but listed as a possible cause if wiring and injector both check out)
How to troubleshoot CAT Engine 26125: first checks
- Bring the engine to normal operating temperature before testing, since many injector solenoid faults only appear once the engine is warm and under load or vibration
- Inspect the connectors and wiring for the Cylinder #6, Injector Actuator #2 circuit closely, looking for corrosion, loose pins, chafed insulation, or pushed-back terminals
- Wiggle-test the harness and connectors under load or vibration conditions similar to when the fault occurs, since intermittent opens may not show up during a static check
- Verify there is no open circuit in the harness between the ECM and the injector connector
- Check the harness sections between the ECM and the valve cover base, and under the valve cover, for damage
- If wiring and connectors check out, test the injector solenoid itself and consider injector replacement
- Only after ruling out wiring, connectors, harness, and injector should the ECM be considered as the cause
How the code clears
No separate clearing step is listed. Correcting the wiring, connector, harness, or injector fault should stop the ECM from continuing to log the code as it retries firing the solenoid. Confirm the fix by running the engine at normal operating temperature and under load or vibration conditions similar to when the fault originally occurred.
Affected models and serial ranges
26125 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 26125 mean?
It means the ECM detected current below the normal level in the #2 solenoid circuit for the Cylinder #6 injector. The ECM sends 105 volt pulses to fire each injector solenoid, and if it senses low current on that circuit, it logs this code while continuing to try firing the injector.
Which CAT engines can set code 26125?
This code applies to C13, C15, C18, C27, and C32 engines equipped with Electronic Unit Injectors.
Is it safe to keep running the engine with this code active?
The ECM keeps attempting to fire the injector rather than shutting the circuit down, so the engine will usually keep running, but expect rough running, misfire, or power loss on that cylinder. It should be diagnosed promptly rather than run indefinitely.
Why does this fault only show up sometimes?
Problems with injector solenoid wiring and connectors often only appear once the engine is warmed up and under vibration from load. A connection that looks fine cold and at idle can fail intermittently once the engine heats up and shakes under working conditions.
What's the difference between low current and high current injector faults?
With low current, the ECM keeps trying to fire the injector. With high current, the ECM disables the solenoid circuit to prevent damage and periodically retries firing it. Code 26125 is the low-current version of this fault.
Do I need to replace the injector to fix this code?
Not necessarily. Wiring, connector, and harness faults are listed as causes before injector replacement. Check the wiring and connectors first, then the harness sections near the ECM and valve cover, and only move to injector or ECM replacement if those check out fine.
Is there a specific reset procedure for this code?
No reset procedure is listed for this code. Once the underlying wiring, connector, harness, or injector issue is repaired, the code should stop being logged as the ECM's retry attempts succeed.