Error Code P0506 is defined as Idle Air Control System RPM Lower Than Expected. It means the Revolution Per Minute (RPM) of the idle control system is lower than expected, a problem usually caused by defective idle air control motor and vacuum leaks, which leads to loss of power in the engine’s performance.

This error code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system, especially those made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.


Error Code P0506 means the PCM (powertrain control module) has detected an engine idle speed lower than the pre-programmed RPM.

This error code is commonly found among vehicles with electronic throttle control. These are vehicles without a regular throttle cable from the accelerator pedal to the engine. Rather, they depend on the sensors and electronics to control the throttle.

Common Symptoms

Aside from the activation of the Check Engine light, rough and unpredictable riding are the most common symptoms of this code. This is because the idle speed is lower than normal. Also, the engine may stall when the car comes to a stop.

Possible Causes

There are lots of factors that may contribute to this code, such as:

  • Defective idle air control motor
  • Vacuum leaks
  • Defective or dirty throttle body
  • Blockage in the exhaust or air intake
  • Defective power steering pressure switch
  • Issue in integral engine counterpart
  • Faulty PCM valve
  • Defective PCM (rare)

How to Check

As with other error codes, technicians diagnose this code using an OBD-II scanned to get all the codes present in the PCM and verify.

Then, they view the freeze frame data to determine the conditions when the code is set. They will then clear the code(s) and then take the vehicle for a test drive replicating the conditions to see whether the code(s) comes back.

Then they will use the OBD-II scanner to view the data stream and compare the current engine idle RPM with the RPM set by the manufacturer for the vehicle.

Next, they will test the engine idle RPM by turning the air conditioner on and heater blower motor. At this stage, they will put the engine under various loads to find out if the PCM can keep a normal engine idle speed.

Then, they will check the throttle body for signs of vacuum leaks and high carbon buildup. If there is high carbon buildup, then the throttle body must be cleaned.

They would have to check the live data on the OBD-II scanner to see if the idle air control system and PCM are working properly.

How to Fix

There are as many ways to repair this code as its causes. Of course, that would need a thorough diagnosis to determine the specific cause of the problem. Common repairs for this code are:

  • Replacement of the defective idle air control motor
  • Replacement of vacuum leaks
  • Replacement of idle air control valve
  • Cleaning dirty throttle body
  • Replacement of defective throttle body
  • Clearing the blockages in the exhaust or air intake
  • Replacement of the defective PCV valve
  • Replacement of the power steering pressure switch
  • Diagnosis and repair of other codes stored in the PCM
  • Replacement or reprogramming of the PCM

Error Code P0506 causes the engine to lose power, which could be dangerous.

In some cases, there are codes stored in the PCM other than P0506. Those codes must be checked and properly fixed to avoid misdiagnosis. Also, in many cases, P0506 is caused by carbon buildup or vacuum leaks, so these components must be checked.