CAT 25 Fault Code: Engine Injector Cylinder #02 : Current Below Normal
Engine Injector Cylinder #02 : Current Below Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 25, SPN 652 FMI 5, means the ECM detected low current flow (an open circuit) on the injector solenoid for cylinder #2 on C13 and C15 engines. The ECM keeps trying to fire the injector, but the underlying wiring or injector problem needs to be fixed to restore normal operation.
High severity. An open circuit on one injector solenoid means that cylinder is not firing correctly, which causes rough running, power loss, and potential misfire damage over time. It is not an immediate shutdown emergency, but it should be diagnosed soon rather than run indefinitely.
What does CAT error code 25 mean?
This code applies to CAT C13 and C15 engines equipped with Electronic Unit Injectors (EUI). Each injector has its own solenoid, and the ECM sends 105 V 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 injector solenoid circuit. Fault code 25 (SPN 652 FMI 5) sets specifically when the ECM detects low current flow, which points to an open circuit somewhere in the cylinder #2 injector solenoid circuit. When this happens, the ECM keeps attempting to fire that injector rather than shutting it down.
This is different from a high current (short circuit) fault, where the ECM disables the solenoid circuit to prevent damage and periodically retries firing. With an open circuit fault like code 25, the injector circuit stays enabled but is not getting proper current flow, which affects combustion in that cylinder.
Common causes of 25
- Failed injector (internal solenoid winding open or damaged)
- Wiring between the ECM and the valve cover damaged, chafed, or disconnected
- Wiring under the valve cover for the injector harness damaged or corroded
- Plugged oil outlet port on the exhaust valve rocker arm
How to troubleshoot CAT 25: first checks
- Run the engine to normal operating temperature before testing, since injector solenoid problems often only show up when the engine is warmed up and under load or vibration.
- Inspect all wiring and connectors between the ECM and the valve cover carefully, looking for chafing, corrosion, or loose pins. Problems here may only appear under vibration, so wiggle-test harnesses while watching for the fault to reappear.
- Check the wiring under the valve cover that runs to the injector harness for cylinder #2, since this is a common failure point separate from the ECM-to-valve-cover wiring.
- Verify the oil outlet port on the exhaust valve rocker arm is not plugged, since this can be tied to injector solenoid performance issues on these engines.
- Test the injector solenoid itself for cylinder #2 to determine if the injector has failed internally.
How the code clears
No separate clearing step is listed. The fault should clear once the open circuit in the injector solenoid wiring, connectors, or the injector itself is repaired and the ECM detects normal current flow again.
Affected models and serial ranges
25 appears in our records across 2 CAT 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 |
Frequently asked questions
What does CAT fault code 25 mean?
It means the ECM on a C13 or C15 engine detected low current flow, an open circuit, on the injector solenoid circuit for cylinder #2. SPN 652 identifies the injector cylinder #2 circuit and FMI 5 identifies the current below normal (open circuit) condition.
Can I keep driving or operating with code 25 active?
The ECM will keep trying to fire the affected injector, so the engine may still run, but cylinder #2 is not firing correctly. This typically causes rough running and power loss, and running for an extended period with a misfiring cylinder risks further engine issues, so it should be diagnosed and repaired promptly.
Why does this fault only show up sometimes?
Injector solenoid wiring problems often only appear once the engine is warmed up and under load or vibration. A wire or connector that looks fine when cold and idling may open up once the engine is hot and working hard, which is why inspection should be done at normal operating temperature.
Is this a wiring problem or an injector problem?
It can be either. CAT lists four possible causes: a failed injector, damaged wiring between the ECM and the valve cover, damaged wiring under the valve cover for the injector harness, or a plugged oil outlet port on the exhaust valve rocker arm. Each needs to be checked to isolate the actual cause.
What is the difference between code 25 and a short circuit injector code?
Code 25 (FMI 5) is an open circuit, low current flow, condition. A short circuit (high current flow) is a separate condition where the ECM disables the solenoid circuit to prevent damage and periodically retries firing. Code 25 does not disable the circuit, it keeps trying to fire the injector.
What voltage does the injector solenoid normally receive?
The ECM sends 105 V pulses to each injector solenoid, timed and sized for the current engine load and speed. Code 25 indicates the circuit is not carrying normal current despite these pulses being sent.