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.
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.
The IAC valve manages the engine idle speed by increasing and decreasing the airflow as required.
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.
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.
Most symptoms may be noticeable only when your vehicle is idle. Apart from an illuminated Check Engine Light, the common DTC P0505 signs that’ll help you diagnose an IAC malfunction are:
DTC P0505 is a severe code.
Once an illuminated Check Engine Light and P0505 code show up, it’s best to get a mechanic to resolve the issue before driving your vehicle.
With a DTC P0505, your vehicle may stall randomly at stop signs or in traffic. You may also notice your fuel economy worsening over time. Moreover, driving around with this trouble code will further damage your car’s engine.
A faulty idle control motor or carbon build-up in the IAC are the common causes of the P0505 code. Here are some more reasons why code P0505 may occur:
If you misdiagnose error code P0505, you may replace or repair unnecessary parts to resolve this error code. It’s best to have an expert look at your vehicle when you spot an issue.
Your mechanic may follow the below steps to diagnose the P0505 trouble code:
The P0505 code may be due to software, mechanical, and technical issues. Here’s what a mechanic may do to resolve error code P0505:
The cost of an IAC valve replacement depends on your car’s make, model, and local labor rates. Usually, it may cost around $120 to $500. This includes both spare parts ($70 – $400) and labor charges ($50 – $100).
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