CAT 16 Fault Code: Engine Injector Cylinder #01 : Current Above Normal
Engine Injector Cylinder #01 : Current Above Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 16 (SPN 651 FMI 6) means the ECM detected high current flow, a short circuit, in the cylinder #1 injector solenoid circuit on C13 and C15 engines. The ECM disables that solenoid circuit to prevent damage but periodically retries firing the injector. This keeps repeating until the short is fixed.
High severity. The ECM shuts down the affected injector circuit to protect itself, which means cylinder #1 is not firing correctly. This causes rough running, power loss, and possible misfire-related engine damage over time if left unaddressed. Not an immediate stop-the-engine emergency, but it should be diagnosed soon.
What does CAT error code 16 mean?
CAT fault code 16, SPN 651 FMI 6, points to the injector solenoid circuit for cylinder #1 on C13 and C15 engines equipped with Electronic Unit Injectors (EUI). Each injector has a solenoid that the ECM fires with 105 V pulses timed and shaped for the current engine load and speed.
This specific FMI 6 code means the ECM saw high current flow, a short circuit, in that cylinder's solenoid circuit. When that happens the ECM disables the solenoid circuit to prevent damage from the excess current, but it will keep periodically trying to fire the injector. If the short is still present, this disable-and-retry cycle repeats indefinitely.
Because the ECM is fighting a short circuit rather than a simple open wire, this code usually points to damaged insulation, a pinched wire, or a failed injector solenoid rather than a loose connector alone.
Common causes of 16
- Failed injector (solenoid internally shorted)
- Wiring between the ECM and the valve cover damaged or shorted
- Wiring under the valve cover for the injector harness damaged or shorted
- Plugged oil outlet port on the exhaust valve rocker arm
How to troubleshoot CAT 16: first checks
- Run the engine to normal operating temperature before testing, since injector solenoid problems typically show up once the engine is warmed up and under vibration from heavy loads
- With the engine warm, inspect wiring and connectors closely for chafing, corrosion, or pinched insulation between the ECM and the valve cover
- Check the injector harness wiring under the valve cover, since it can develop faults that only appear under vibration
- Inspect the oil outlet port on the exhaust valve rocker arm for cylinder #1 for blockage
- Wiggle-test wiring and connectors while watching for the code to reset, since intermittent shorts often only show up under vibration or load
How the code clears
No separate clearing step is listed. Once the failed injector, damaged wiring, or plugged rocker arm oil outlet port is repaired, the ECM should stop detecting the short circuit and stop cycling the solenoid circuit off and on.
Affected models and serial ranges
16 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 16 mean?
It means SPN 651 FMI 6, a high current (short circuit) condition detected by the ECM in the cylinder #1 injector solenoid circuit on C13 and C15 engines. The ECM disables that circuit to protect itself but keeps trying to fire the injector periodically.
Can I keep driving or working with code 16 active?
The engine will likely run rough or lose power because cylinder #1 is not firing normally. It is not necessarily an immediate shutdown situation, but it should be diagnosed and repaired soon to avoid extended misfire and possible engine damage.
What usually causes this code?
CAT lists four causes: a failed injector, damaged wiring between the ECM and the valve cover, damaged injector harness wiring under the valve cover, or a plugged oil outlet port on the exhaust valve rocker arm.
Why does this fault often show up only when the engine is warm?
Problems with an injector solenoid circuit typically occur once the engine reaches normal operating temperature and while it is under vibration from heavy loads. That is why diagnosis should be performed with the engine warmed up.
Is this the same as an open circuit injector code?
No. FMI 6 is specifically a high current, short circuit condition. A low current, open circuit condition on the same injector would trigger a different code.
How do I find an intermittent short in the injector wiring?
Since the wiring or connectors may only fault under vibration, inspect and flex the harness between the ECM and valve cover and under the valve cover while the engine is warm and running, watching for the code to reactivate.