CAT 56 Fault Code: Engine Injector Cylinder #05 : Current Above Normal
Engine Injector Cylinder #05 : Current Above Normal · ai-assisted, editor-reviewed · Last updated 2026-07-21
TL;DR
CAT code 56 (SPN 655 FMI 6) sets when the ECM detects high current flow, a short circuit, through the solenoid circuit for injector cylinder #5 on C13 and C15 engines. The ECM disables that solenoid circuit to prevent damage but keeps periodically trying to fire the injector, so the fault will keep recurring until the short is fixed.
High severity. The ECM shuts down the affected injector solenoid circuit to protect itself, which means cylinder #5 stops firing correctly. This causes a running imbalance, power loss, and rough operation, and the ECM will keep retrying the circuit, which can repeat the fault and stress the wiring further if the short is not corrected.
What does CAT error code 56 mean?
This code points to a high current condition, essentially a short circuit, somewhere in the electrical path that fires injector solenoid #5. The ECM sends 105 V pulses to each injector solenoid at a precise time and duration for the given engine load and speed. When the ECM senses current flow above what it expects for that circuit, it flags this code and disables the solenoid circuit to keep the high current from damaging the ECM driver or the injector wiring.
Because the ECM does not give up on the cylinder, it will periodically try firing the injector again. If the short is still present, the code will set again and the disable/retry cycle repeats. This is different from a low current (open circuit) condition, where the ECM keeps trying to fire the injector without disabling the circuit, since there is no damage risk from an open.
Caterpillar notes that solenoid problems often show up once the engine is warmed up and under load or vibration, so a cold, no-load check in the shop may not reproduce the fault even though it is very real on the road or under heavy work.
Common causes of 56
- A failed injector, most likely an internal short within the solenoid winding itself
- Wiring between the ECM and the valve cover that has chafed, pinched, or shorted to another conductor or to ground
- Wiring under the valve cover, specifically in the injector harness, damaged by heat, vibration, or oil contamination
- A plugged oil outlet port on the exhaust valve rocker arm, which Caterpillar lists as a related cause
How to troubleshoot CAT 56: first checks
- Run the engine up to normal operating temperature before testing, since Caterpillar states that solenoid wiring problems often only show up once warm and under load or vibration
- Inspect the wiring and connectors between the ECM and the valve cover carefully for chafing, pinched insulation, or corrosion, paying close attention to any spot that could touch a grounded or powered surface under vibration
- Remove the valve cover and inspect the injector harness wiring underneath it for damage, oil saturation, or heat degradation near cylinder #5
- Check the oil outlet port on the exhaust valve rocker arm for plugging, since Caterpillar ties this to the code even though it is a lubrication path rather than a wiring fault
- Test or swap the injector solenoid for cylinder #5 if the wiring and connectors check out clean, since a failed injector solenoid is listed as a direct cause
- Watch for the fault repeating under load or vibration even if it does not show at idle, since the ECM will keep retrying the circuit and resetting the code if the short is intermittent
How the code clears
No separate clearing step is listed for this code. Once the shorted wiring, connector, plugged oil port, or failed injector is corrected, the ECM should stop detecting high current on the circuit and stop disabling and retrying the solenoid. Verify the fix by running the engine to normal operating temperature and under load, since Caterpillar notes this is when the fault is most likely to reappear if the repair is incomplete.
Affected models and serial ranges
56 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 56 mean on a C13 or C15 engine?
It means the ECM detected current flow above normal on the solenoid circuit for injector cylinder #5, which the ECM reads as a short circuit. The ECM disables that solenoid circuit to protect itself and periodically retries firing the injector.
Can I keep running the engine with code 56 active?
You can usually keep running, but cylinder #5 will not be firing correctly while the circuit is disabled, which causes a power imbalance and rough running. Since the ECM keeps retrying a shorted circuit, it is best treated as a High severity issue that should be diagnosed soon rather than ignored.
What is the difference between code 56 and code 55?
Code 55 (SPN 655 FMI 5) is Current Below Normal, an open circuit condition on the same injector cylinder #5 solenoid circuit, where the ECM keeps trying to fire the injector without disabling anything since there is no short-circuit damage risk. Code 56 is the opposite: Current Above Normal, a short circuit, which causes the ECM to disable the solenoid circuit.
Why does code 56 only show up when the engine is warm or under load?
Caterpillar notes that injector solenoid wiring problems, including shorts, often only appear once the engine reaches normal operating temperature and is under vibration from heavy loads. A cold, no-load check may pass even though the fault is real.
Could a plugged oil port really cause an electrical current fault?
Caterpillar lists a plugged oil outlet port on the exhaust valve rocker arm as one of the causes tied to this code, alongside the injector and wiring causes. The exact mechanism is not detailed, but it is worth checking along with the electrical causes.