Toyota Prius P0505: Idle Air Control System- Malfunction

P0505 This OBDII code deals with the idle control system of the Toyota Prius.  It’s a generic code, which means that it has the same meaning for the Prius as it would any other vehicle (Prius or not).

P0505:  Idle Air Control System:  Malfunction

P0505 triggers when there is either a stuck or clogged idle control valve or a vacuum leak.  Other causes can also be involved.  Although, they aren’t as prevalent.

P0505 Toyota Prius


Índice de Contenido
  1. P0505 Symptoms:  Toyota Prius
  2. Prius P0505 Causes
    1. Valve for Idle Air Control
    2. Vacuum Leak
    3. Carbon Buildup
  3. Conclusion

P0505 Symptoms:  Toyota Prius

This particular trouble code lets you know that there is something wrong with the idle air control system, but that’s about it.  These symptoms could be different.

These are the top symptoms of P0505.

  • Soon, Service engine light
  • It is a rough idle
  • Stalling
  • Very high idle speed 


Prius P0505 Causes

P0505 can usually be caused either by a vacuum leak or an issue with the idle control valve.  While replacing the idle air control valve seems like a good idea, it’s worth your time to check for a Vacuum leak first.

Toyota Prius P0505 Diagnosis

Valve for Idle Air Control

The idle air control valve’s primary job is to regulate the idle speed of your engine.  This is done by making sure that the engine's idle speed is maintained at the correct level.

It is possible for the IAC to become stuck or dirty.  It may need to be replaced or cleaned.  Here’s a great Video from YouTube Here are some tips on cleaning an idle valve.  

You may need to replace your idle air valve if you feel it is time. It is very affordable.


Vacuum Leak

While the idle air control valve is often the cause of P0505, it’s a great idea to start diagnosing it by looking for a vacuum leak.  Examine the vacuum tubes near the IAC.  You may need to replace the vacuum tubes around the IAC if they are cracked or dry rotted.

You can code your Prius by leaking around the throttle and intake leaks.  Here’s a great article from Popular Mechanics on How to locate a vacuum leak.


Carbon Buildup

Carbon buildup can occur around the IAC's inlet.  It is possible to fix this problem by checking the IAC inlet area for blocked passages.

It can cause the intake of air to be reduced if the throttle body becomes too dirty.  This can cause P0505 to be thrown.  Often, when this is the case, you’ll feel the engine stall for a second before it recovers when slowing down.  

This happens because the engine can’t adjust to this problem fast enough.  This problem is usually solved by cleaning the area around the throttle blades.



It's possible to identify P05055 in your Prius.  Most of the time it’s a vacuum leak or the idle air control valve.  If you feel like there’s anything that you can add, please feel free to leave a comment below.

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