CAT Engine 26105 Fault Code: Cylinder #5 Injector Actuator #2:Current Below Normal
Also called Cylinder #5 Injector Actuator #2 - Current Below Normal, Cylinder #5 Injector Actuator #2 : Current Below Normal
Cylinder #5 Injector Actuator #2:Current Below Normal · ai-assisted, editor-reviewed · Last updated 2026-07-21
TL;DR
Code 26105 (SPN 3663 / FMI 5) means the ECM detected low current flow on the #2 solenoid circuit of the Cylinder #5 injector. This points to an open or high-resistance path in the wiring, connectors, or injector solenoid itself, not a short. The ECM keeps trying to fire the injector while the fault is active. Affects C13, C15, C18, C27, and C32 engines with Electronic Unit Injectors.
Medium severity. A single injector running on low current usually causes a rough-running or misfiring cylinder rather than an immediate shutdown, but leaving it unaddressed risks unburned fuel, poor combustion, and possible damage to the injector or ECM driver over time. Diagnose within the shift rather than running it indefinitely.
What does CAT Engine error code 26105 mean?
This code applies to engines with Electronic Unit Injectors (EUI) that are electronically controlled. 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 26105 sets when the ECM detects low current flow on the #2 solenoid of the Cylinder #5 injector, which is an FMI 5 condition, essentially an open circuit or excessive resistance rather than a dead short. Because current is low rather than absent, the ECM continues trying to fire the injector rather than shutting the circuit down.
This is different from a current-above-normal condition (see code 26106), where the ECM detects a short and disables the circuit to prevent damage, retrying it periodically.
Common causes of 26105
- Damaged, corroded, or loose connectors or wiring in the injector solenoid circuit
- An open circuit in the 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
- An electronic problem within the injector solenoid, including a failing solenoid that needs replacement
- An intermittent fault that only shows up under vibration or once the engine reaches normal operating temperature
- A faulty ECM (less common, checked only after wiring and injector are ruled out)
How to troubleshoot CAT Engine 26105: first checks
- Run the engine to normal operating temperature before testing, since these faults often only appear once the engine is warmed up or under load and vibration
- Inspect the connectors and wiring for the Cylinder #5 injector circuit for corrosion, looseness, chafing, or damage, paying close attention to connector pins
- Check the harness between the ECM and the injector connector, and the harness section between the ECM and the valve cover base and under the valve cover, for opens or high resistance
- Wiggle-test the harness and connectors while watching for the code to reset, since the problem may only appear under vibration and not with the engine sitting still
- Verify continuity through the full length of the solenoid circuit wiring back to the ECM to rule out an internal open
- If wiring and connectors check out, test the injector solenoid itself for proper resistance and consider that the injector may need replacement
- Only after wiring, connectors, and injector are confirmed good should the ECM be suspected as a cause
How the code clears
No separate clearing step is listed. Once the open circuit or high-resistance connection is repaired, or the faulty injector or harness section is replaced, the code should stop being generated on subsequent engine cycles. No reset procedure is listed for this code beyond correcting the underlying wiring, connector, injector, or ECM fault.
Affected models and serial ranges
26105 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 26105 mean?
It means the ECM detected low current flow on the #2 solenoid of the Cylinder #5 injector. This is typically caused by an open circuit or high resistance in the wiring, connectors, or the injector solenoid itself, not a short.
Can I keep running the engine with code 26105 active?
The ECM will keep trying to fire the affected injector, so the engine will likely keep running, but expect rough running, a misfire on that cylinder, or reduced performance. It is best to diagnose the wiring and injector as soon as practical rather than running 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 heavy loads. A wire or connector that reads fine cold and at idle can open up intermittently once the engine is hot and shaking under load.
What is the difference between code 26105 and code 26106?
Code 26105 is a current-below-normal (open circuit type) fault on the same Cylinder #5 Injector Actuator #2 circuit, while code 26106 is current-above-normal, meaning the ECM detected a short and disabled the circuit to prevent damage. They point to opposite electrical failures: an open or high-resistance path for 26105 versus a short circuit for 26106.
How is this different from codes 26125 and 26126?
Codes 26125 and 26126 are the same current-below-normal and current-above-normal faults but on the Cylinder #6 Injector Actuator #2 circuit instead of Cylinder #5. The diagnostic logic is the same, just applied to a different cylinder's injector.
Do I need to replace the injector to fix code 26105?
Not necessarily. Wiring, connector, and harness problems are common causes and should be checked first. The injector solenoid itself, or in rarer cases the ECM, is only replaced after the wiring and connectors are confirmed to be in good condition.
What voltage does the ECM send to the injector solenoids?
The ECM sends 105 volt pulses to each injector solenoid, timed and sized for the current engine load and speed. Code 26105 is set when the current resulting from those pulses on the #2 solenoid circuit is measured as too low.