How to Fix Code P0505: Easy Steps for Vehicle Owners

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When you are peacefully driving, and suddenly the check engine light pops up, what is the first thing you will do? You will probably grab your OBD scanner to find out it's a P0505 error code. Don’t fret, though, as we are here to help you!

This article will tell you the symptoms, causes, and possible fixes for the P0505 trouble code. So the next time this shows up, you will be ready to fix it yourself without any problems. Let’s talk about what this diagnostic code means.

What is the Code P0505?

The P0505 is a generic code that means that the Idle Air Control (AIC) system has malfunctioned. The AIC System ensures that the engine's idle speed is within a specific range. When the Powertrain Control Module (PCM) detects an incorrect voltage on one or more IAC motor circuits, it will trigger P0505.

Symptoms of Code P0505

Aside from the illuminated check engine light, P0505 is associated with several symptoms. So if you have this trouble code on your scanner tool, you might experience symptoms including:

  • Hesitation or stumbling when the engine is started
  • Rough idle
  • Too high idle speed
  • Too low idle speed
  • The engine stalls intermittently

Causes of Code P0505

Same with any other trouble code, P0505 has several causes. Here are some of the reasons that trigger this trouble code.

  • Faulty or dirty IAC valve (common)
  • Clogged air filter
  • Vacuum leak
  • Malfunctioning TPS (Throttle Position Sensor)
  • Bad MAP sensor
  • Faulty PCM

How to diagnose Error Code P0505?

The best way to find the exact issue triggering the P0505 code is to diagnose the possible causes of the problem. All you need is an OBD scanner tool. Once you have identified the problem, there are usually easy fixes that owners can do themselves. So how to start diagnosing?

Step-by-Step Guide

  • Connect your scanner tool to the DLC (Data Link Connector) located under the dash on the driver's side.
  • Once connected, turn on the ignition and select the P0505 code from the codes list. The scanner will               then provide you with a description of what is causing the code.
  • Make sure to save all the codes in the ECM engine control module (ECM)before clearing.
  • Perform a road test and monitor if the engine idles stay within specifications in and out of gear.
  • Check for vacuum leaks.
  • Check the throttle plates and IAC valve inlet for carbon build-up.
  • Disconnect the IAC to double-check that the vehicle's base idle is within specification.
  • Remove the IAC and examine it for obstructed passageways.

How to Fix Code P0505?

After diagnosing the problem, you can start fixing it. You can have it done by a professional mechanic if you are not skilled in automobile repair. But if you think you can do it yourself, you can follow the steps below. Some of the fixes that you might try include:

Step-by-Step Guide to Cleaning the Throttle Plates and IAC Valve Inlet

  • To get started, disconnect the battery before beginning any work on the electrical system.
  • Start spraying throttle cleaner onto the plates once you have the engine bay open. Let it sit for a few               minutes before wiping it off with a clean rag. If there is any dirt or carbon build-up on the IAC valve inlet,         you can use a Q-tip dipped in throttle cleaner to clean it off.
  • If the throttle cleaner doesn't do the trick, you might need to replace the IAC valve.

Step-by-Step Guide to Replacing the IAC valve

This is an easy job that you or the mechanic can do in less than an hour. Be sure to buy a new valve from an authorized dealer so that you know it will fit correctly. To get started.

  • Disconnect the electrical connector from the valve.
  • Remove the bolts that hold the valve in place. Be careful not to lose any of the screws, as they can be             easily misplaced.
  • Install the new valve in reverse order, securely reconnecting all of the hoses and bolts.
  • Before closing up the engine bay, don't forget to reattach the electrical connector.
  • Once you've replaced the IAC valve, start up your vehicle and check for the P050 code. If it's gone, you're         good to go!

Step-by-Step Guide to Adjusting the Engine Idle Speed

This process will vary depending on your car's make and model, so consult your owner's manual for instructions. In most cases, you'll need to adjust the engine idle speed screw located on the throttle body to get the engine running at a steady pace. To begin:

  • If your engine is cold, start it and let it run until the radiator fan kicks on.
  • Turn off the engine and wait a few minutes for the car to cool down.
  • Locate the engine idle speed screw on the throttle body (it will be either located near or on top of the             throttle plate).
  • Slowly turn the screw clockwise or counterclockwise until you achieve the desired idle speed. Turning the       screw clockwise will increase the idle speed, while turning it counterclockwise will do the opposite.
  • Start the engine and let it run for a few minutes to ensure that the idle speed is still correct. If not, repeat       these steps as necessary.

Step-by-Step Guide to Repairing Vacuum Leak

One possible cause of the P050 code is a vacuum leak. A vacuum leak can be caused by many things, such as a cracked hose or loose-fitting. If that's the case, there are a few steps you can take to troubleshoot and fix the issue:

  • Inspect all of the hoses and fittings for damage or leaks.
  • Use a vacuum cleaner to inspect the area around the intake manifold and throttle body for any leaks.
  • If you can't find the leak, try spraying a light mist of water over suspected areas while the engine is                   running. Any escaping steam will indicate a leak.

Once you have made your repairs, clear the codes from the ECM and road test the vehicle again. On the other hand, after doing all the repairs, if the code persists, a more serious problem with the engine might need to be diagnosed and fixed by a professional.

Common Mistakes When Diagnosing the P0505 Code

People make mistakes when diagnosing code P0505 due to several symptoms associated with this code. It is expected, mainly when you have limited knowledge about car engines. These are the most common mistakes people make. 

  • Replacing the IAC valve when there is a vacuum leak
  • Not checking for carbon build-up on throttle plates and IAC valve inlet
  • Replacing the TPS sensor when it's not necessary
  • Clearing ECM codes without repairing the underlying problem
  • Not removing excessive carbon in the IAC passages if replacing the IAC valve

Code P0505 FAQs

1. Is the P0505 code Serious?

Since the P0505 code is associated with many causes, including the Faulty PCM vacuum leak, which can cause the engine to run rough, you should take it seriously. Another reason is that you cannot pass the emission testing while having an illuminated check engine light, so if you can address the problem as soon as possible, do it!

2. Is it okay to drive with this trouble code?

Yes, you can continue to drive the vehicle with this trouble code as long as it doesn't affect your car's drivability. There are only a few instances wherein the code will cause problems like stalling or rough idling.

3. What devices can I use to diagnose the P0505 code?

There are many devices that you can use to diagnose the P05005 code. You can use an OBD-II scanner, a digital volt/ohmmeter (DVOM), or a scan tool.

4. Can I clear this trouble code without repairing the underlying problem?

Yes, you can clear this trouble code without repairing the underlying problem, but it will come back on if the problem still exists.

5. How much does a mechanic usually charge for diagnosing the code P0505?

There is no set cost for diagnosing code P05050. The price can vary depending on the type of device you use and the time it takes to diagnose the problem.


The P0505 code may sound serious, indicating an issue with the Idle Air Control (IAC) Valve. However, this problem is easy enough to fix yourself if you are car-savvy. But if you have little to no experience, it is always best to seek a professional mechanic’s help.

We hope this article walked you through your journey to diagnosing and fixing your car or gave you a good understanding of code P0505. So next time you encounter this error, you'll be able to take care of it without any trouble! Thank you for reading.