Injector Cutoff

📖 YOUCANIC Automotive Glossary

Injector Cutoff is a bidirectional scanner function that commands the ECU to disable the fuel injector for a specific cylinder while the engine is running. This is the controlled, scanner-managed version of the power balance test concept — by cutting fuel to one cylinder at a time and monitoring the effect on engine operation, you can isolate which cylinder has a problem. When a healthy cylinder’s injector is cut off, you should hear and feel a noticeable change in engine operation (RPM drop, rougher running). If cutting a cylinder makes little or no difference, that cylinder was already not contributing — confirming it as the problem cylinder.

Injector Cutoff is particularly useful for diagnosing misfires and rough running when DTCs have not pinpointed a specific cylinder (P0300 Random Misfire), for verifying injector operation (if cutting the injector makes no change, the injector may already be dead), and for isolating mechanical problems (low compression). The YOUCANIC UCAN-II allows individual injector cutoff control through the Active Test menu. This test should be performed with the engine at operating temperature and idle, and only briefly for each cylinder — extended operation with a disabled cylinder can damage the catalytic converter from unburned oxygen.