CAT 74 Fault Code: Cylinder #5 Injector current fault
Also called Cylinder #5 Injector current high, Cylinder #5 Injector current low, Cylinder #6 Injector current high, Cylinder #6 Injector current low, Cylinder 5 Fault
Cylinder #5 Injector current fault · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 74 (SPN 655 / FMI 5) means the ECM detected a low current (open circuit) or high current (short circuit) condition while trying to fire the No. 5 or No. 6 cylinder injector solenoid on a C11, C13, C15, or C18 engine. It usually points to wiring, connector, or injector solenoid problems rather than a fuel quality issue.
High severity. An injector that won't fire correctly means a dead or misfiring cylinder, which causes rough running, power loss, and potential unburned fuel washing the cylinder. It should be diagnosed before continued heavy-load operation.
What does CAT error code 74 mean?
Code 74 covers a family of related injector fault descriptions: Cylinder #5 Injector current fault, Cylinder #5 or #6 Injector current high or low, and Cylinder 5 Fault. All of them trace back to the same SPN 655 / FMI 5 diagnostic, which means the ECM sees an electrical current problem on an injector solenoid circuit.
These engines use hydraulic electronic unit injectors that are hydraulically actuated and electronically energized. The ECM sends a 105 volt pulse to each injector solenoid at the correct time and duration for the given engine load and speed. The solenoid sits on top of the injector body. If the ECM does not see the current response it expects when it fires that pulse, either too little (open circuit, low current) or too much (short circuit, high current), it logs code 74.
One important wiring detail: two injector solenoids share a supply wire. That means a single open or short in a shared supply wire can trigger diagnostic codes on two injectors at once, so if you see this code alongside a fault for the paired cylinder, check the shared wiring first before condemning two separate injectors.
What triggers a CAT 74 code?
The ECM logs this code when it detects a low current (open circuit) condition during five consecutive attempts to energize the No. 5 or No. 6 injector, while battery voltage stays above 9 VDC for the last two seconds. This confirms the fault is in the injector circuit itself and not caused by low battery voltage at the time of the attempt.
Common causes of 74
- ECM connection or harness problem at the ECM connector
- Injector solenoid failure (open or short circuit in the solenoid itself)
- Valve cover connector for the injector solenoids, loose or corroded
- Wiring harness between the ECM and the valve cover, chafed or open
- Injector harness under the valve cover, damaged or disconnected
- Failed injector (mechanical or electrical)
- Mechanical cylinder failure
- Failed ECM
How to troubleshoot CAT 74: first checks
- Check the ECM connector and its wiring harness for corrosion, loose pins, or damage before touching the injector itself.
- Inspect the valve cover connector for the injector solenoids since this is a common point for moisture intrusion and corrosion.
- Trace the harness between the ECM and the valve cover looking for chafe points, pinched wire, or breaks, especially near mounting points and moving components.
- Pull the valve cover and inspect the injector harness underneath for damage, since this is a documented failure point separate from the outer engine harness.
- If a second injector on the same shared supply wire also has a logged code, check that shared supply wire first rather than replacing both injectors.
- Test the injector solenoid itself for the expected open or short circuit condition using appropriate electrical test procedures for hydraulic electronic unit injectors.
- Confirm battery voltage is stable and above the threshold the ECM checks for, so you're not chasing a wiring fault caused by a power supply issue.
How the code clears
No separate clearing step is listed. Once the underlying wiring, connector, solenoid, or injector fault is repaired and the ECM confirms the injector responds correctly to the 105 volt pulse over successive attempts, the code should not re-log. If it returns immediately after repair, recheck the shared supply wire and the ECM connector before assuming a new component has failed.
Affected models and serial ranges
74 appears in our records across 4 CAT 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 |
| C18 | Serial range not listed in source records |
Frequently asked questions
What does CAT code 74 mean?
It means the ECM tried to fire the No. 5 or No. 6 cylinder injector solenoid and detected either a low current condition (open circuit) or a high current condition (short circuit) instead of the expected response. This is SPN 655 with FMI 5.
Which CAT engines can throw fault code 74?
This code applies to C11, C13, C15, and C18 engines that use hydraulic electronic unit injectors.
Can a bad connector on one injector cause a code on another cylinder?
Yes. Two injector solenoids share a supply wire, so an open or short circuit in that shared wire can generate diagnostic codes for two injector solenoids at once. Always check the shared wiring if two related codes appear together.
Is low battery voltage the cause of this code?
No. The ECM only logs this code when battery voltage is confirmed above 9 VDC for the last two seconds, which rules out a simple low-voltage condition as the trigger.
Do I need to replace the injector if I get code 74?
Not necessarily. Probable causes range from ECM connection issues and harness damage to actual injector solenoid or injector failure. Check wiring and connectors under the valve cover and between the ECM and valve cover before condemning the injector.
Is it safe to keep running the engine with this code active?
It's not recommended for extended heavy-load operation. A misfiring or non-firing cylinder can cause rough running, power loss, and unburned fuel issues in that cylinder, so it should be diagnosed as soon as practical.
What's the difference between the No. 5 and No. 6 versions of this code?
Both follow the same logic and set-conditions, five consecutive failed attempts to energize the injector with battery voltage confirmed above 9 VDC. The only difference is which cylinder's injector circuit is affected.