What is P0505?
Diagnostic trouble code P0505 is defined as “Idle Control System Malfunction.”
The idle control system controls the engine speed when the vehicle is idle. It does so through an Idle Air Control valve (IAC valve) located at the IAC passages inside the engine throttle body.
Note: The IAC motor or valve is usually used in cars with Multiport Electronic Fuel Injection Systems.Â
The throttle plate closes when a vehicle is idle (or when you release the accelerator pedal.) This limits the air supply to the engine. To allow the engine to run smoothly when the vehicle isn’t moving, the IAC valve bypasses the closed throttle plate, and continues to inject air into the engine.Â
The IAC valve manages the engine idle speed by increasing and decreasing the airflow as required.Â
When more power is needed, the powertrain control module (PCM) commands the idle control system to adjust the airflow into the engine. This helps the engine produce the required power to run major components like the air conditioning, power steering, etc., efficiently.Â
The powertrain control module monitors the airflow through voltage variations in the IAC circuit. It sets code P0505 when it detects an irregular voltage in any IAC circuit.