Fuel injectors are devices that introduce the appropriate amount of air/fuel mixture into the cylinders. They allow the engine to achieve good ignition and power performance.
In most cases, the injectors are controlled by the Engine Control Module (ECM), which makes comparisons between the power output of each cylinder and the crankshaft speed.
The diagnostic code P0263 OBDII will be set if the ECM detects power irregularities in cylinder 1, which differ from the values stored and specified by the manufacturer.