CAT 16 Fault Code: Engine Injector Cylinder #01 : Current Above Normal
Engine Injector Cylinder #01 : Current Above Normal · ai-assisted, editor-reviewed · Last updated 2026-07-21
TL;DR
CAT fault code 16 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 the solenoid circuit to prevent damage, then periodically retries firing the injector. This is an electrical short condition, not an open circuit.
High severity. The ECM shuts down the affected injector circuit to protect itself, which means cylinder #1 is not firing correctly. Running on fewer cylinders causes rough running, power loss, and potential long-term engine damage if left unaddressed. Diagnose before continued heavy load operation.
What does CAT error code 16 mean?
Fault code 16 (SPN 651 FMI 6) applies to C13 and C15 engines with Electronic Unit Injectors (EUI). Each injector has a solenoid that the ECM fires with 105 V pulses timed for the correct duration based on engine load and speed.
The ECM continuously monitors current flow through each injector solenoid circuit. Code 16 specifically means high current flow, a short circuit, was detected in the cylinder #1 injector circuit. When this happens, the ECM disables that solenoid circuit to prevent damage from the excess current, then periodically attempts to fire the injector again. If the short is still present, this disable-and-retry cycle repeats.
This is different from a low current (open circuit) fault, which would mean a broken wire or lost connection rather than a short. Code 16's high current condition points toward wiring or solenoid insulation that has failed and is allowing current to flow somewhere it should not.
Common causes of 16
- Failed injector, meaning the solenoid winding inside the injector itself has shorted
- Wiring between the ECM and the valve cover has chafed or shorted, often against another powered wire or ground
- Wiring under the valve cover for the injector harness has failed, frequently due to heat and vibration in that space
- Plugged oil outlet port on the exhaust valve rocker arm, which the OEM diagnostic lists as a contributing cause for this circuit
How to troubleshoot CAT 16: first checks
- Run the engine to normal operating temperature before testing. CAT notes that injector solenoid problems typically show up once the engine is warmed up and under vibration from heavy loads, so a cold, no-load check can miss the fault entirely
- Inspect the wiring and connectors between the ECM and the valve cover carefully, looking for chafing, melted insulation, or contact points where the harness could short to another circuit
- Open the valve cover and inspect the injector harness wiring underneath it for chafe points, pinched wire, or damaged insulation, since this section is exposed to heat and constant vibration
- Flex and wiggle the harness at the connectors and along its run while watching for the fault to reappear, since intermittent shorts often only show up under vibration
- Check the oil outlet port on the exhaust valve rocker arm for blockage, since a plugged port is listed as a possible cause tied to this code
- Test the cylinder #1 injector solenoid itself for a short if the wiring and harness check out, since a failed injector is listed as a direct cause
How the code clears
No separate clearing step or reset procedure is listed for this code. Once the short circuit in the injector solenoid wiring or the injector itself is repaired, the ECM should stop disabling the circuit and stop logging the fault on its own during normal operation.
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 fault code 16 mean?
It means the ECM detected high current flow, a short circuit, in the cylinder #1 injector solenoid circuit on a C13 or C15 engine. The ECM disables that circuit to prevent damage and periodically retries firing the injector.
Is fault code 16 safe to keep running with?
Not for long. The ECM is repeatedly disabling and retrying the cylinder #1 injector circuit, which means that cylinder is not firing reliably. Expect rough running and power loss, and get it diagnosed before continued heavy-load operation.
What is the difference between fault code 16 and the low current version of this fault?
Fault code 16 is a high current, short circuit condition. A low current fault on the same circuit would instead mean an open circuit, such as a broken wire or a disconnected pin, which the ECM handles differently by continuing to try to fire the injector without disabling the circuit.
How is fault code 16 different from fault codes 12, 13, or 14?
Those are separate circuits entirely. Code 12 covers coolant level voltage low, code 13 covers fuel temperature voltage high, and code 14 covers medium/high retarder current high. Code 16 is specific to the cylinder #1 injector solenoid current being above normal.
Why does fault code 16 often show up only when the engine is warm?
CAT notes that injector solenoid wiring and connector problems typically surface once the engine reaches normal operating temperature and is under load and vibration. A cold, idling check can miss an intermittent short that only appears under those conditions.
Can a plugged oil port cause fault code 16?
Yes. CAT lists a plugged oil outlet port on the exhaust valve rocker arm as one of the possible causes tied to this code, alongside wiring and injector failures.
Do I need to reset anything after fixing fault code 16?
No separate reset procedure is listed. Once the short in the wiring or injector is repaired, the ECM should stop logging the fault during normal operation.