What is the P0505 Code? | How to Fix P0505 Trouble Code?

When your car’s primary computer, which is often referred to as the powertrain control module (PCM), perceives a problem with the idle air control system, it will warn the driver and record the appropriate diagnostic trouble code. P0505 is a common trouble code for “Idle Control System Malfunction.” This can happen for multiple reasons.

What Does the P0505 Code Mean?

Diagnostic trouble code (DTC) P0505 stands for “Idle Control System,” which means that the computer inside the engine can’t control the idle speed. As a result, the actual idle speed is not the same as the target idle speed. 

p0505 code

How does the Idle Control System work?

Idle air control (IAC) systems are commonly found on or near the throttle body of older automobiles. The main function of the IAC system is to maintain the idle speed by measuring the amount of air passing through the throttle plate’s throat.

When the vehicle is idling, the throttle plate closes, limiting the air supply to the engine. However, the engine still needs air to keep running.

Following instructions from the PCM, the idle control system opens the bypass air passageway. 

By adjusting the size of the bypass air passageway’s opening, the idle control system can manage the amount of air fed to the idling engine. It can raise idle speeds by admitting more air and reduce speeds by decreasing the flow.

The PCM keeps track of the current load on the idling engine. It gets the idle control system to tweak the air supply so that the engine gets the air supply it needs.

The idle air control system undergoes wear and tear like other car parts. When it goes bad, it will affect the engine’s idle speed, which could lead to the PCM issuing a P0505 code.

Read More: Symptoms and causes of a Bad IAC Valve

Symptoms of Code P0505

  • The Check Engine Light will be illuminated, and the code is set in ECM memory.
  • The engine idle may be lower or higher than specifications.
  • If the engine has a vacuum leak, it may have a rough idle
  • The engine may stall when coming to a stop.
  • The engine may idle too high at times.

Causes of Code P0505

There are several potential causes of a code P0505, but the two most likely are a defective idle control motor or an intake manifold vacuum leak. That’s because the idle air control motor typically runs on the vacuum, so if there’s a leak, it won’t work the way it’s supposed to!

The following are the most common causes of P0505 trouble code:

  • A faulty idle air control (IAC) valve
  • A vacuum leak
  • An issue with the IAC circuit, such as damaged wires or poor connections
  • Idle speed out of calibration (relearn required)
  • An issue with the PCM, such as software in need of an update
  • Carbon buildup in IAC valve
  • Carbon buildup in the throttle body

How to diagnose the P0505 code?

  • Clears and verifies the code after it has been scanned and documented in the ECM. 
  • During a driving test, keep a close eye on the engine’s idle to make sure it stays within specs.  
  • Perform a vacuum leak check on the engine.  
  • Tread plates and IAC valve inlets need an inspection for carbon buildup. 
  • To see if the engine’s base idle is within specs, disconnect the IAC. 
  • Examine passageways by removing and inspecting the IAC.  
  • When diagnosing the P0505 code, there are a few common pitfalls. 
  • Without ensuring there is no engine suction leak before replacing the IAC.
  • IAC passages should be cleaned of excessive carbon if the IAC valve is replaced.

FAQ Section

How serious is the P0505 code?

  • Code P0505 indicates the IAC is not working correctly, and it can cause the engine to idle too low or high, and the engine may stall when coming to a stop.
  • The Check Engine Light being on causes the vehicle to fail emission testing.
  • The code may be from the engine has a vacuum leak, and this can cause the engine to run rough and have poor fuel mileage.

What repairs can fix the P0505 code?

  • Inspect the IAC valve and replace it if needed
  • Clean the throttle body and passages
  • Remove carbon from the throttle body and IAC passages and clean IAC
  • Repairing a vacuum leak in the engine intake manifold vacuum system or gaskets

Can I drive my car with a P0505 trouble code?

It is not recommended, but you can drive your car even if the trouble code P0505 is on unless the engine stalls or stutters in a way that makes the car hard to drive.

How do I reset my idle control valve?

Follow the below-given steps to reset the IAC valve without a diagnostic tool:

  1. Press the gas pedal marginally.
  2. Start the engine and let it run for 5-10 seconds.
  3. Turn the ignition to “off.”
  4. Wait 10 seconds.
  5. Start the engine.

Leave a Comment