CAT Engine 26085 Fault Code: Cylinder #4 Injector Actuator #2:Current Below Normal
Also called Cylinder #4 Injector Actuator #2 - Current Below Normal, Cylinder #4 Injector Actuator #2 : Current Below Normal
Cylinder #4 Injector Actuator #2:Current Below Normal · ai-assisted, editor-reviewed · Last updated 2026-07-21
TL;DR
Code 26085 (SPN 3662 / FMI 5) means the ECM detected low current flow in the circuit for the #2 solenoid on the #4 cylinder's electronic unit injector. The ECM keeps trying to fire the injector, but low current usually points to an open circuit, damaged wiring, a bad connector, or a failing injector solenoid.
Medium severity. The engine will typically keep running because the ECM continues attempting to fire the injector, but a persistent low-current fault on one injector solenoid causes rough running, misfire-like symptoms, and possible loss of power on that cylinder. Diagnose it within the shift rather than ignoring it, since intermittent wiring issues tend to get worse under load and vibration.
What does CAT Engine error code 26085 mean?
This code applies to C13, C15, C18, C27, and C32 engines with Electronic Unit Injectors (EUI) that are electronically controlled and, on some models, mechanically actuated as well. 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 constantly monitors current flow through each solenoid circuit. Code 26085 sets specifically when the ECM detects low current flow (FMI 5, current below normal) in the circuit feeding the #2 actuator solenoid on the #4 cylinder injector. This is different from a current above-normal condition, which points to a short rather than an open or high-resistance circuit.
When this fault is active, the ECM does not give up on the injector. It keeps trying to fire it on schedule, so the symptom is often rough running or reduced power from that cylinder rather than a complete shutdown of the injector.
Common causes of 26085
- Damaged, corroded, or loose connectors or wiring in the injector solenoid circuit
- An open circuit somewhere 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
- A wire with an actual break or opening rather than a full disconnect, which can cause an intermittent low-current condition especially under vibration
- A faulty or worn injector solenoid on the #4 cylinder's #2 actuator
- An electronic problem within the injector itself
- A faulty ECM, in cases where wiring and injector both check out
How to troubleshoot CAT Engine 26085: first checks
- Run the engine to normal operating temperature before testing, since injector solenoid problems typically show up warmed up and under load or vibration, not at idle or cold
- With the engine off, inspect all connectors in the injector solenoid circuit for corrosion, looseness, or damage, paying close attention to connectors near the valve cover base and under the valve cover
- Check the wiring harness between the ECM and the injector connector for chafing, pinches, or breaks, flexing the harness by hand to try to reproduce an intermittent open under simulated vibration
- Verify there is no open circuit in the harness section between the ECM and the connector using appropriate continuity testing procedures
- If wiring and connectors check out, test the injector solenoid itself for a low-current or open condition, and consider swapping or testing the injector to isolate a solenoid fault from a harness fault
- Only after ruling out wiring, connectors, and the injector should the ECM be suspected as the cause
How the code clears
No reset procedure or separate clearing step is listed for this code. Once the underlying wiring, connector, injector, or ECM issue is repaired and the ECM no longer detects low current in the #4 cylinder's #2 actuator circuit, the active fault should clear on its own. Confirm with a diagnostic tool that the code does not return after a test run at normal operating temperature and under load.
Affected models and serial ranges
26085 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 26085 mean?
It means the ECM detected low current flow (current below normal) in the circuit for the #2 solenoid on the #4 cylinder's electronic unit injector. SPN 3662, FMI 5.
Will code 26085 shut down the engine?
Not by itself. The ECM continues trying to fire the injector even with the fault active, so the engine typically keeps running, though you may notice rough running or reduced power from that cylinder.
What is the difference between code 26085 and code 26086?
26085 is a current below-normal (low current, open-circuit type) fault on the #4 cylinder's #2 injector actuator. 26086 is the current above-normal (short-circuit type) fault on the same actuator. Low current points to opens, bad connectors, or broken wiring; high current points to shorts that make the ECM disable the solenoid circuit to prevent damage.
Why does this fault only show up when the engine is warmed up or under load?
Wiring and connector problems in injector circuits are often intermittent and worsen with heat expansion and engine vibration under heavy load. That is why diagnostic procedures call for testing at normal operating temperature and flexing the harness to try to reproduce the fault.
Can a bad connector alone cause this code?
Yes. Damaged, corroded, or loose connectors in the injector solenoid circuit are listed as a leading cause and should be checked before assuming the injector or ECM is at fault.
Do I need to replace the injector to fix code 26085?
Not necessarily. Wiring, harness, and connector issues are more common causes and should be ruled out first. Injector solenoid failure and, less commonly, a faulty ECM are also possible causes if wiring checks out clean.