P0505 - OBD-II Trouble Code

Auto Systems and Repair

Idle Control System Malfunction

Our emissions expert has put together the following information about the P0505 fault code. We have also included diagnostic procedures you can take to your repair shop if the mechanic is having difficulty analyzing the code.

OBD II Fault Code

  • OBD II P0505

Fault Code Definition
The purpose of the Idle Control System is to manage the engine idle speed. This is often controlled by an Idle Air Control Motor mounted on or near the Throttle Body of the Intake Manifold. In some cases, an Idle Air Stepper Valve or Motor is used. To raise or lower the engine Idle speed, the Powertrain Control Module (PCM) opens or closes either of these devices to allow more or less air by the Throttle Plate in the Throttle Body. This is done in order to meet the ever-changing loads placed on the engine, such as the use of air conditioning, heat, and wipers.


  • Check Engine Light will illuminate
  • Engine idle speed is very low and may die at stops
  • Engine idles rough
  • In some cases, engine may idle very high

Common Problems That Trigger the P0505 Code

  • Defective Idle Air Control Motor
  • Intake Manifold Vacuum leaks
  • Carbon buildup in the Throttle Body air passages

Common Misdiagnosis

  • Idle Air Control Motor is replaced when code P0505 was triggered by carbon buildup in the Throttle Body air passages and Idle Air Control Motor
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