P0505: Idle Control System Malfunction

What does the P0505 error code mean?

The diagnostic trouble code P0505 means your car has detected an “Idle Control System Malfunction.” The code triggers when the idle air control system goes bad in some way. There are a number of faults that can cause this code, including a vacuum leak. When your car’s primary computer, or powertrain control module, detects a fault with the idle air control system, it will notify the driver via this diagnostic trouble code as well as a check engine light.

Why is this issue important?

The idle control system relies on an idle air control valve, typically located on or near your car’s throttle body. It does what it says on the box: When your car idles, the throttle is closed, which limits the air supply heading into the engine. The engine does still need some air to keep going, however, and at the request of the car’s powertrain control module, the idle control system will open a bypass air system that allows a little air into the engine to keep it running. This, too, can be adjusted by the system, allowing more or less air in as needed while the car is at idle.

Can I safely drive my car with this error code?

It could be possible to drive a short distance with a P0505 code, but it’ll certainly be difficult if not downright hazardous. The faulty idling system will most likely present itself in the form of stalls, with your engine shutting down once it reaches an idle or when you stop hitting the gas pedal. It’s best not to drive the car while this code is active — the car may end up stalled somewhere you don’t want to be.

Common symptoms of the P0505 error code

• Engine stalling at idle
• High or low idle speed
• Trouble starting your car
• The check engine light is on

How is the P0505 error code diagnosed?

• Code verification: Use an OBD-II scanner to confirm the presence of the P0505 (or related) code.
• Visual inspection: Inspect your engine’s intake system for vacuum leaks, damaged hoses or loose connections.
• Idle air control valve test: Inspect and test the idle air control valve for carbon buildup or electrical failure.
• Throttle body inspection: The mechanic will examine the throttle body for dirt or debris that may affect airflow.
• Wiring and connector check: Inspect electrical wiring and connectors leading to the idle air control valve for corrosion or damage.
• Check powertrain control module functionality: The mechanic will test the powertrain control module outputs to see if all physical components appear to be in working order.

How is the P0505 error code repaired?

• Clean or replace the idle air control valve if clogged or faulty.
• Repair or replace damaged vacuum hoses or intake components.
• Fix or replace any corroded or broken wiring or connectors.
• Reprogram or replace the powertrain control module if it is found to be defective.
• Clear the code and test the vehicle to ensure symptoms are removed.

Related reading

On-board diagnostics (OBD-II) and diagnostic trouble codes are part of your car's self-diagnostic system. The five-character alphanumeric code identifies the part and problem. Check out Edmunds’ growing database of diagnostic trouble code information here.