CAT Engine 105 Fault Code: Cylinder #10 Injector : Current Below Normal
Also called Cylinder #10 Injector Current Below Normal, Cylinder #10 Injector Open Circuit, Cylinder #10 Injector current below normal, Cylinder #10 Injector open circuit, Cylinder #10 Injector:Current Below Normal, Injector Cylinder 10 Open Circuit, Injector Cylinder 10 open circuit
Cylinder #10 Injector : Current Below Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT fault code 105 (SPN 10 / FMI 5) means the ECM has detected low current or an open circuit in the cylinder #10 injector solenoid circuit on C15, C175, C27, and C32 engines. The ECM keeps trying to fire the injector while the code is active. This usually points to wiring, connectors, or the injector solenoid itself rather than a catastrophic failure, but it can cause a rough-running or misfiring cylinder until fixed.
Medium severity. The ECM continues attempting to fire the injector when this code is active, so the engine will typically keep running, often with a misfire or power loss on cylinder #10. It is not an immediate shutdown condition, but leaving it unaddressed risks continued rough running, uneven wear, and potential escalation if wiring damage worsens. Diagnose within the shift rather than ignoring it.
What does CAT Engine error code 105 mean?
CAT code 105 applies to the cylinder #10 injector on C15, C175, C27, and C32 engines equipped with Electronic Unit Injectors (EUI). Each injector has two solenoids, and the ECM sends 105 volt pulses to each solenoid at a timing and duration matched to engine load and speed.
The ECM continuously monitors current flow through each solenoid circuit. This code, current below normal / open circuit, is set when the ECM detects unusually low current or an open in that circuit. When this happens, the ECM does not shut the injector off, it keeps trying to fire it.
This is different from a high-current or short-circuit condition, where the ECM would disable the solenoid circuit to prevent damage and periodically retry. For code 105 specifically, the concern is a weak or broken electrical path to the injector solenoid, not a short.
What triggers a CAT Engine 105 code?
The ECM detects an open circuit or low current flow in the cylinder #10 injector solenoid circuit. Once detected, the ECM logs the code and continues attempting to fire the injector solenoid rather than disabling it.
Common causes of 105
- Electronic problem with the injector itself
- Damaged, corroded, or loose connectors and wiring in the injector circuit
- Problem in the wiring harness, including the harness section between the ECM and the valve cover base, or under the valve cover
- An open in a wire within the injector circuit
- A faulty injector that needs replacement
- A faulty injector solenoid
- A faulty ECM (less common, but listed as a possible cause)
- Intermittent problems that only show up under engine vibration or heavy load
How to troubleshoot CAT Engine 105: first checks
- Run the engine to normal operating temperature before testing. Problems with the injector solenoid typically show up once the engine is warmed up and under load or vibration.
- With the engine at normal operating temperature, carefully inspect the connectors and wiring for cylinder #10's injector circuit for corrosion, looseness, chafing, or damage. Wiggle-test connectors and harness sections since faults often only appear under vibration.
- Trace and inspect the harness between the ECM and the valve cover base, and the harness section under the valve cover, for damage or opens.
- Check the injector solenoid circuit for continuity to rule out an open wire.
- If wiring and connectors check out, test the injector solenoid itself, since a faulty solenoid or injector is a listed cause.
- If the injector and wiring both test good, consider the ECM as a possible cause, though this is the least common root cause listed.
How the code clears
No separate clearing step is listed. The ECM logs the code and continues trying to fire the cylinder #10 injector solenoid; once the underlying wiring, connector, injector, or ECM issue is repaired, the code should stop being active on the next diagnostic cycle. No manual reset procedure is described.
Affected models and serial ranges
105 appears in our records across 4 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C15 | Serial range not listed in source records |
| C175 | Serial range not listed in source records |
| C27 | Serial range not listed in source records |
| C32 | Serial range not listed in source records |
Frequently asked questions
What does CAT fault code 105 mean?
It means the ECM detected low current flow or an open circuit in the cylinder #10 injector solenoid circuit on a CAT C15, C175, C27, or C32 engine. The ECM keeps trying to fire that injector while the fault is active.
Is CAT code 105 the same as SPN 10 FMI 5?
Yes. CAT fault code 105 corresponds to SPN 10 / FMI 5, which is the standard diagnostic identifier for cylinder #10 injector current below normal or open circuit.
Can I keep running the engine with code 105 active?
The ECM will keep trying to fire the injector, so the engine typically keeps running, but expect a misfire, rough idle, or power loss on that cylinder. It's best to diagnose and repair it promptly rather than run indefinitely, since the underlying cause could be wiring damage that worsens over time.
What usually causes this code, wiring or the injector itself?
Both are listed as common causes. Damaged, corroded, or loose connectors and wiring, including harness sections between the ECM and valve cover base or under the valve cover, are frequently cited. A faulty injector or injector solenoid, and less commonly a faulty ECM, are also possible causes.
Why does this fault often only show up when the engine is warm or under load?
Problems with the injector solenoid circuit, especially wiring and connector issues, often only appear once the engine reaches normal operating temperature and is under vibration from heavy load. That's why diagnostic procedures call for testing at normal operating temperature and checking connectors for vibration-related intermittent faults.
Do I need to reset the ECM after fixing code 105?
No separate clearing or reset procedure is described for this code. Once the wiring, connector, injector, or solenoid issue is repaired, the fault should clear on its own during normal engine operation.
Does code 105 mean I need a new injector?
Not necessarily. A faulty injector or solenoid is one possible cause, but damaged wiring, connectors, or harness sections are equally likely culprits and should be ruled out first before replacing the injector.