What does it mean?
Fuel atomization is critical to the performance and efficiency of the internal combustion engine. In combination with the heat of the engine and cylinder compression, as well as the swirl effect of the intake air, the modern fuel injector does a pretty good job atomizing and vaporizing fuel for combustion. When the engine is cold, however, fuel tends to remain in its liquid form, which does not burn.
More fuel needs to be injected to compensate for lower vaporization, resulting in less efficient cold engine operation and increased emissions. To improve fuel vaporization, particularly with a cold engine, some automakers have adopted the air-assisted fuel injection system. The system pulls air from the intake, before the throttle plate, and routes it to the fuel injectors via hoses, tubes, or intake manifold channels.
Fuel is injected in the normal manner, using electrical pulses from the ECM (engine control module), into a small chamber. There, vacuum from the intake manifold pulls air into the chamber, swirling with the fuel, leading to better atomization. Then, the air-fuel mixture enters the cylinder, where it is fully vaporized for combustion. Depending on system design, air-assist may be controlled by a dedicated solenoid valve or by the idle speed control valve.
Generally-speaking, the ECM increases air-assist when the engine is cold and is running at idle or part-throttle (low-speed low-load), to maximize the effect of engine vacuum on the system. At higher temperatures and throttle openings, the air-assist system is not active. The ECM (engine control module) uses feedback from the air-fuel ratio (AFR) sensor to monitor the air-assist system.
If the ECM detects that the air-assisted fuel injector system is malfunctioning, either letting too much air into the system or not enough, it sets a DTC (diagnostic trouble code) in system memory, P0065 – Air Assisted Injector Control Range/Performance, and illuminates the malfunction indicator lamp (MIL).
Note: A Range/Performance related code will be set when either a sensor or other component does not perform within the range the PCM (Powertrain Control Module) expects to see, given the current engine load/speed, and information gathered from other sensors.
The possible causes of Range/Performance codes are likely to be defective sensors as easily as they are likely to be the result of wiring issues that affect the operation of the affected sensor or component, which means that with these codes, it is important to regard all sensors and components as part of the control circuit the code refers to.