CAT Engine 26025 Fault Code: Cylinder #1 Injector Actuator #2:Current Below Normal
Also called Cylinder #1 Injector Actuator #2 - Current Below Normal, Cylinder #1 Injector Actuator #2 : Current Below Normal
Cylinder #1 Injector Actuator #2:Current Below Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT fault code 26025 (SPN 3659 / FMI 5) means the ECM detected low current flow on the #2 solenoid circuit of the cylinder #1 injector. This applies to C13, C15, C18, C27, and C32 engines with Electronic Unit Injectors. The ECM keeps trying to fire the injector, but low current usually points to a wiring, connector, or injector solenoid problem rather than a total failure.
Medium severity. This code alone does not shut the engine down since the ECM keeps attempting to fire the injector. But an injector that is not firing correctly on one cylinder can cause misfire, rough running, and lost power. If related high-current codes also appear, the ECM may disable that solenoid circuit, which is a more serious condition. Diagnose within the shift rather than ignoring it long term.
What does CAT Engine error code 26025 mean?
Cylinder #1 injector actuator #2 refers to one of the two solenoids inside that cylinder's Electronic Unit Injector (EUI). The Engine Control Module (ECM) sends 105 volt pulses to each solenoid at a precise time and duration based on engine load and speed.
The ECM continuously monitors current flow through each solenoid circuit. Code 26025 sets when the ECM detects current flow below the expected level on this specific solenoid circuit. Unlike a high-current short, the ECM does not disable the circuit for a low-current fault. It keeps trying to fire the injector, which can mean intermittent or weak injector operation on that cylinder rather than a complete stoppage.
Because this is a below-normal current fault, the root cause is almost always resistance in the circuit: a loose or corroded connector, chafed wiring, or a degraded solenoid winding, rather than a dead short.
Common causes of 26025
- Damaged, corroded, or loose connectors or wiring in the injector solenoid circuit
- An open or high-resistance section in the wiring harness between the ECM and the injector connector
- A faulty harness section between the ECM and the valve cover base, or under the valve cover itself
- A bad or failing injector solenoid
- An internal ECM fault (less common, checked only after wiring and injector are cleared)
How to troubleshoot CAT Engine 26025: first checks
- Run the engine to normal operating temperature first. Problems with injector solenoids typically show up once the engine is warmed up and under vibration from load, so testing cold or at idle can miss the fault.
- Inspect all connectors in the injector solenoid circuit for corrosion, looseness, bent pins, or moisture intrusion. Wiggle test wiring and connectors while watching for the code to reset, since intermittent faults often only appear under vibration.
- Check the wiring harness between the ECM and the valve cover base, and the harness under the valve cover, for chafing, pinches, or damage from heat or vibration.
- Verify there is no open circuit in the harness between the ECM and the injector connector using a proper continuity check with the harness disconnected from the ECM.
- If wiring and connectors check good, test the injector solenoid itself. If the solenoid is confirmed faulty, replace the injector.
- Only after wiring, connectors, and injector are ruled out, consider the ECM as a possible cause.
How the code clears
No separate clearing step is listed. Once the wiring, connector, harness, or injector problem is repaired and current flow returns to normal, the ECM should stop logging the fault on subsequent operation. Confirm the repair by running the engine under load and vibration conditions similar to when the fault originally occurred, since that is when injector solenoid problems typically surface.
Affected models and serial ranges
26025 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 26025 mean?
It means the ECM detected current flow below normal on the #2 solenoid of the cylinder #1 injector (SPN 3659 / FMI 5). The injector has two solenoids, and this fault is specific to one of them on cylinder #1.
Which engines can set fault code 26025?
C13, C15, C18, C27, and C32 CAT engines equipped with Electronic Unit Injectors (EUI) can set this code.
Will code 26025 shut down my engine?
Not directly. Since it is a low-current fault rather than a short, the ECM keeps trying to fire the injector instead of disabling the circuit. However, it can cause rough running or a slight power loss on that cylinder, and it should be diagnosed promptly.
Why does this fault only show up when the engine is warmed up or under load?
Wiring and connector problems related to injector solenoids often only appear under vibration from heavy load or once components have expanded from heat. That is why the diagnostic procedure calls for testing at normal operating temperature and under conditions similar to when the fault occurs.
What is the most common cause of this code?
Damaged, loose, or corroded connectors and wiring in the injector solenoid circuit are the most frequently cited causes, followed by harness problems near the valve cover and a faulty injector solenoid.
Do I need to replace the injector if I get this code?
Not necessarily. Wiring, connectors, and harness sections should be inspected and ruled out first. The injector solenoid itself is only replaced if it tests faulty after the wiring checks come back clean.
Could the ECM itself be the problem?
It is possible but uncommon. ECM replacement is listed as a possible cause only after connectors, wiring, harness sections, and the injector solenoid have all been checked and ruled out.