CAT 67 Fault Code: Engine Injector Cylinder #06 : Not Responding Properly
Engine Injector Cylinder #06 : Not Responding Properly · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 67, SPN 656 FMI 7, means the ECM detects that the cylinder #6 injector solenoid is not responding as expected even though the ECM continues to send it power. The engine keeps running on the affected injector's commands, but the feedback the ECM expects back is wrong or missing. This code requires the Fuel System Verification Test to clear.
Medium severity. The engine keeps running and the ECM continues to energize the injector solenoid, so this is not an immediate shutdown event. But an unresponsive injector on a working cylinder can cause rough running, power loss, or misfire-like symptoms under load, and it should be diagnosed before it leads to bigger problems with wiring or the injector itself.
What does CAT error code 67 mean?
This code applies to Electronic Unit Injectors (EUI), which are injectors with a built-in solenoid that the ECM controls directly. The ECM sends 105 V pulses to each injector solenoid at the timing and duration needed for the current engine load and speed. When the ECM commands cylinder #6's injector to fire but does not see the response it expects, it logs code 67.
Importantly, the ECM does not shut off the injector when this code sets. It keeps energizing the solenoid and logs the fault so a technician can investigate. That means the symptoms may be subtle at idle and show up more clearly under load or once the engine reaches normal operating temperature.
Problems like this often show up intermittently, particularly when the engine is warmed up or under vibration from heavy loads. This points toward wiring and connector issues as much as the injector itself, since vibration can cause a marginal connection to fail only under certain conditions.
Common causes of 67
- Failed injector: the solenoid or internal components of the cylinder #6 injector have failed and are not responding correctly to the ECM's commands.
- Wiring between the ECM and the valve cover: damaged, corroded, or loose wiring in this run can disrupt the signal or power path to the injector.
- Wiring under the valve cover for the injector harness: this wiring is exposed to heat and vibration inside the valve cover area and can develop faults that only appear once the engine is warm or working hard.
- Plugged oil outlet port on the exhaust valve rocker arm: a blocked oil outlet port in this area can affect the injector's operating environment and contribute to the fault.
How to troubleshoot CAT 67: first checks
- Bring the engine to normal operating temperature before testing, since problems with the injector solenoid typically show up once the engine is warmed up.
- Visually inspect the wiring and connectors between the ECM and the valve cover, and the injector harness wiring under the valve cover, looking for corrosion, chafing, loose pins, or damaged insulation.
- While the engine is running, watch for symptoms that come and go with vibration under load, since wiring and connector issues often only appear during vibration and may not show up at idle or at rest.
- Check the oil outlet port on the exhaust valve rocker arm for cylinder #6 to confirm it is not plugged.
- Plan to run the Fuel System Verification Test as part of the diagnostic process, since this is required to clear the code.
How the code clears
The Fuel System Verification Test must be performed in order to clear a code with FMI 7 like this one. No separate clearing step is listed beyond running that test. Because wiring and connector problems related to this code can be vibration-related, perform the verification procedure with the engine at normal operating temperature and pay close attention to wiring and connector condition throughout the test.
Frequently asked questions
What does CAT code 67 SPN 656 FMI 7 mean?
It means the ECM commanded the cylinder #6 injector solenoid to fire but did not get the response it expected. The ECM logs the fault and continues to energize the injector solenoid rather than shutting it down.
Will the engine keep running with code 67 active?
Yes. The ECM continues to energize the injector solenoid after logging this code, so the engine keeps running, though you may notice rough running or power loss related to that cylinder, especially under load or once the engine is warm.
How do I clear CAT fault code 67?
You must perform the Fuel System Verification Test. No separate clearing step is listed for this code beyond running that test.
Why does this code only show up when the engine is warm or working hard?
Problems with the injector solenoid and its wiring often only appear once the engine reaches normal operating temperature and while under vibration from heavy loads. A wiring or connector fault can be intermittent and only show up under those conditions, so testing at operating temperature is recommended.
What are the possible causes of code 67?
Four causes are identified: a failed injector, damaged wiring between the ECM and the valve cover, damaged wiring under the valve cover for the injector harness, or a plugged oil outlet port on the exhaust valve rocker arm.
Is a plugged oil outlet port really connected to an injector fault code?
Yes, a plugged oil outlet port on the exhaust valve rocker arm for the affected cylinder is listed as one of the causes for this code, so it should be checked along with the injector and wiring.