CAT 65 Fault Code: Engine Injector Cylinder #06 : Current Below Normal
Engine Injector Cylinder #06 : Current Below Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 65, SPN 656 FMI 5, means the ECM detected low current flow (an open circuit) on the injector solenoid circuit for cylinder #06 on C13 and C15 engines. The ECM keeps trying to fire the injector, but the low current condition means the solenoid isn't getting the drive it needs.
High severity. This code affects fuel delivery to one cylinder. The engine can keep running but with a misfire on cylinder #06, which causes rough running, power loss, and possible long-term injector or wiring damage if left unaddressed. Diagnose before returning the machine to heavy-load service.
What does CAT error code 65 mean?
CAT code 65 (SPN 656, FMI 5) applies to C13 and C15 engines equipped with Electronic Unit Injectors (EUI). Each injector has a solenoid that the ECM fires with 105 V pulses timed to engine load and speed. The ECM constantly monitors current flow through each injector solenoid circuit to make sure each pulse is doing its job.
FMI 5 specifically means the ECM sees low current flow, which points to an open circuit somewhere in the injector #06 solenoid wiring path. When this happens, the ECM does not just give up: it keeps attempting to fire the injector on every cycle, hoping the connection re-establishes itself.
This is different from a short circuit condition (high current), where the ECM would disable the circuit to prevent damage. With an open circuit, the risk is more about a cylinder not firing correctly, which shows up as rough running, lost power, or increased vibration under load.
Common causes of 65
- Failed injector (the solenoid winding itself may be open internally)
- Wiring between the ECM and the valve cover has a break, chafe, or corrosion causing an open circuit
- Wiring under the valve cover for the injector harness has failed, often from heat cycling or vibration
- Plugged oil outlet port on the exhaust valve rocker arm, which can indirectly affect injector operation in this cylinder
How to troubleshoot CAT 65: first checks
- Run the engine to normal operating temperature before testing. Problems with injector solenoids typically show up when the engine is warmed up and under vibration from heavy loads, so testing cold can miss the fault entirely.
- With the engine at operating temperature, inspect wiring and connectors between the ECM and the valve cover closely for chafing, corrosion, or loose pins. Wiggle-test connectors while watching for the code to reset, since some wiring faults only appear under vibration.
- Pull the valve cover and inspect the injector harness wiring underneath for damage, cracked insulation, or corrosion at the injector connectors.
- Check the oil outlet port on the exhaust valve rocker arm for cylinder #06 to confirm it is not plugged.
- If wiring and connectors check out, test the injector solenoid itself for an open winding, since a failed injector is a listed cause.
How the code clears
No separate clearing step is listed for this code. Once the underlying wiring, connector, injector, or rocker arm oil port issue is repaired, the ECM should stop detecting the low current condition and the code should clear on its own after further engine operation.
Affected models and serial ranges
65 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 code 65 mean on a C13 or C15 engine?
It means the ECM detected low current flow, an open circuit, on the injector solenoid circuit for cylinder #06. The ECM keeps trying to fire the injector even with this fault active.
Can I keep running the engine with code 65 active?
The engine will typically keep running since the ECM keeps attempting to fire the injector, but expect rough running and power loss from the affected cylinder. It's best to diagnose and repair before extended heavy-load operation.
Why does this code only show up sometimes?
Injector solenoid wiring problems often only appear when the engine is warmed up and under vibration from heavy loads. A wire or connector that looks fine cold may open up once hot and vibrating.
Is code 65 the same as a short circuit fault?
No. Code 65 (FMI 5) is a low current, open circuit condition. A short circuit (high current) would be a different FMI, and in that case the ECM disables the circuit to prevent damage rather than continuing to try firing it.
What parts should I check first for code 65?
Start with the failed injector itself, the wiring between the ECM and the valve cover, the injector harness wiring under the valve cover, and the oil outlet port on the exhaust valve rocker arm for plugging.
Does this code affect only cylinder #06?
Yes, SPN 656 with this description is specific to the injector solenoid circuit for cylinder #06 on C13 and C15 engines.