CAT Engine 45 Fault Code: Cylinder #4 Injector : Current Below Normal
Also called Cylinder #4 Injector - Current Below Normal, Cylinder #4 Injector Current Below Normal, Cylinder #4 Injector Open Circuit, Cylinder #4 Injector current below normal, Cylinder #4 Injector open circuit, Cylinder #4 Injector: Current Below Normal, Cylinder #4 Injector:Current Below Normal, Cylinder 4 Open, Engine Injector Cylinder #04 : Current Below Normal, Injector Cylinder 4 Open Circuit, Injector Cylinder 4 open circuit
Cylinder #4 Injector : Current Below Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT fault code 45 (SPN 654 / FMI 5) means the ECM detected an open circuit, low current condition in the No. 4 cylinder injector solenoid or its wiring. The engine will run with a misfire and low power on that cylinder while the ECM keeps trying to fire the injector. This affects C11, C13, C15, C175, C18, C27 and C32 engines.
Medium severity. The engine will keep running with a misfire and reduced power rather than shutting down, so this is not an immediate stop-now situation. However, ignoring it risks continued rough running, possible damage to the affected cylinder or injector, and unnecessary fuel or oil dilution over time, so it should be diagnosed within the shift rather than left indefinitely.
What does CAT Engine error code 45 mean?
CAT engine fault code 45, also logged as SPN 654 FMI 5, points to an open circuit or low current condition in the solenoid or wiring for the No. 4 cylinder's electronic unit injector (EUI). These engines use mechanically actuated, electronically energized injectors. The ECM fires each injector solenoid with a 105 volt pulse timed precisely for the current engine load and speed. When the ECM tries to fire the No. 4 injector and does not see the expected current draw, it flags this code.
The ECM does not give up: it keeps attempting to operate the injector after logging the code. But an open circuit physically prevents that injector from firing, so the cylinder stops contributing power. The result is a noticeable misfire and a loss of overall engine power, along with rough running that gets worse under load.
Because the fault is tied to a wiring or solenoid problem rather than a fuel or mechanical issue, it often shows up more when the engine is warmed up or working hard under vibration, conditions that stress connectors, harness insulation and solder joints already on the edge of failing.
What triggers a CAT Engine 45 code?
The ECM sets this code when it detects a low current (open circuit) condition for each of five consecutive attempts to fire the No. 4 injector, while battery voltage is above 9 volts DC for 2 seconds. This combination confirms the ECM tried repeatedly under valid electrical conditions and never saw the injector respond.
Common causes of 45
- Injector, harness or ECM connectors not fully coupled or properly seated
- Corrosion, abrasion, or pinch points in the injector or engine wiring harness
- A short or open circuit specific to the No. 4 cylinder's injector wiring
- A short in the engine harness or in common ECM wiring shared between cylinders
- Faulty or worn-out No. 4 cylinder injector solenoid
- Damaged injector harness under the valve cover, or a damaged valve cover base wire harness
- Faulty ECM (rare, but listed as a possible cause if all wiring and injector checks pass)
- Improper injector adjustment or engine valve clearance
- Fault at the connection point between the ECM and the valve cover base
How to troubleshoot CAT Engine 45: first checks
- Visually inspect all injector connectors and harness connectors at the ECM and valve cover for full seating, corrosion, or pin damage
- Check the engine wiring harness for chafe points, pinch points, or abrasion, especially near the valve cover and areas exposed to engine vibration under load
- Run an injector cutout test to compare the No. 4 injector's response against the other cylinders; a faulty injector will show a low reading versus the rest
- Check for a short or open specifically isolated to the No. 4 cylinder circuit versus a fault in wiring shared with other cylinders
- Confirm injector codes are correctly programmed into the ECM if any injector or the ECM itself has recently been replaced
- Inspect the injector solenoid mounted atop the injector body for physical damage or corrosion
How the code clears
No separate clearing step is listed beyond correcting the underlying wiring, connector, or injector fault. The ECM will keep attempting to fire the injector on its own once the open circuit is repaired, and the code should stop being active once current flow to the injector solenoid is restored. If a short circuit rather than an open circuit is present, the ECM will disable and periodically retry the solenoid circuit until the short is corrected.
Affected models and serial ranges
45 appears in our records across 7 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C11 | Serial range not listed in source records |
| C13 | Serial range not listed in source records |
| C15 | Serial range not listed in source records |
| C175 | Serial range not listed in source records |
| C18 | 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 45 mean?
It means the ECM detected an open circuit or low current condition on the No. 4 cylinder injector solenoid or its wiring, logged as SPN 654 FMI 5. The injector is not drawing the current the ECM expects when it tries to fire it.
Can I keep running the engine with code 45 active?
The engine will keep running because the ECM continues trying to fire the injector, but expect a misfire, rough running, and low power, especially under load. It is not a shutdown code, but it should be diagnosed promptly to avoid ongoing rough operation.
Is code 45 caused by a bad injector or bad wiring?
It can be either. Possible causes include damaged connectors, harness corrosion or pinch points, a short in the engine harness, a faulty injector solenoid, or in rarer cases a faulty ECM. An injector cutout test comparing all cylinders helps narrow it down.
Do I need to reprogram anything if I replace the injector?
Yes. Each unit injector has a four-digit injector code (from its serial number) that must be programmed into the ECM to compensate for manufacturing variation. If you replace any injector or the ECM itself, you must reprogram the injector codes, or the ECM will generate a separate check programmable parameters code.
Why does this fault seem to show up more when the engine is warmed up or under heavy load?
Faults with the injector solenoid and its wiring typically surface once the engine reaches operating temperature and is under vibration from heavy loads, conditions that stress marginal connections and wiring more than idle or light-load running.
What is the difference between code 45's open circuit and a short circuit condition?
An open circuit prevents the injector from firing at all and the ECM keeps trying continuously. A short circuit causes the ECM to disable the solenoid circuit temporarily, then retry it; if the short remains, this cycle repeats until the fault is fixed.
Which CAT engines can trigger fault code 45?
This code applies to the C11, C13, C15, C175, C18, C27, and C32 engine models, specifically referencing the No. 4 cylinder's electronic unit injector circuit.