P0505 Honda 1.6 – Test your Civic IAC

When you have a P0505 Honda OBDII trouble code, there’s something wrong with the idle air controller in your Honda. Today I’ll be showing you how to test your Civic IAC to resolve the Honda trouble code, and the specific model we are working on is a 1997 Honda Civic EX. This Civic is equipped with the 1.6 liter SOHC D16 engine, and the Idle Air Controller (IAC) specific OBDII code can be easily tested using the two pin connector on the IAC itself.

Some of the common issues and P0505 symptoms can vary, but because of the idle control air valve malfunction your Civic may not want to stay running. When you turn on the engine and your D16 doesn’t stay on or want to stay running without accelerator input and your Honda Civic check engine light is on, this may be one of the leading issues at hand. The idle air control valve that we’ll be replacing here is part number 16022-P2A-J01, and this unit is connected to your front water pipe and uses a check valve to introduce air into your engine to maintain idle.


1996-2000 Honda Civic – D16Y7

How To Test my Honda Civic IAC


Using a scan tool you can easily test the function of your Civic Idle Air Control valve, but before you do that you should check the list of check engine codes stored in your DTC section of your ECU. If your Honda Civic has a stored P1508 or P1509 check engine code, stop here and address those issues before taking a look at your P0505 Idle Air Control Valve error.

Once you have determined that your MIL is reporting a P0505 Honda DTC trouble code, you must access the real time data viewer section of your scan tool. If your scan tool does not have this feature, it’s a good idea to pick one up. All you will really need to check is Engine speed, engine coolant temperature and engine load.

  1. Start your Honda Civic engine
  2. Make sure the transmission is in neutral or PARK
  3. Raise the emergency parking brake
  4. Rev and hold at 3,000 RPM.
  5. Once the engine warms up and radiator fan turns on, let off throttle
  6. Check throttle position to ensure your throttle is closed.
  7. Check your scan tool – Make sure it’s around 10%
  8. Check engine temperature through your scan tool. It should be within 190º-205ºF or 90º-96ºC.
  9. Disconnect the IAC valve controller

At this point your engine speed should increase artificially, raising your idle significantly if you own an automatic. If you own a manual transmission equipped Honda Civic, your RPM will fail once the IAC is disconnected.

If your engine does not respond the right way, remove and replace your Honda Civic Idle Air Controller using our guideline below.

Where is my Honda Civic Idle Air Control Valve Located?


This valve is mounted to the back of your intake manifold, and placed over the two ports on the back of the intake manifold chamber. This valve is has coolant passages within it to lower operating noise and vibration, and it’s mounted to the back of your intake manifold with two 12mm bolts.


There’s two pins that are part of your engine harness that connect to the Idle Air Controller. One of the first steps to testing your Honda Civic is to start your engine and unplug the IAC to see if there is a change in your P0505 Honda trouble code or idle.

How Do I Remove the IAC?

Removing and servicing your Honda Civic IAC is easy and straightforward to do, and all you need is a needle nose plier and a 12mm wrench. It might be a good idea to try this job when your engine is cold, because it does involve removing the coolant lines that run to the control valve. As with all of our checkenginetroublecode.com guides and writeups, we are not responsible for any damage that occurs from this guide either directly or indirectly. Always disconnect the negative terminal on your battery before working on it, and make sure to wear the proper eyewear and use all the proper steps for safety.


Using your needle nose, loosen and remove the coolant hoses shown above and circled in orange. The coolant line to the right runs to your throttle body, and once you have these lines removed, you can undo the 12mm bolts and remove the Honda Civic IAC.


Once these 12mm bolts are yanked out, the Honda Civic IAC is free and can be removed. Now you can do one of two things here to test your Idle Air Controller. You can turn the key to the “ON” position to test for power at the wiring terminal, or start the engine to see if your IAC valve moves. Replace your Idle air control valve using the part numbers above, and clear your P0505 OBDII trouble code using your scan tool.

You have now resolved your P0505 OBDII check engine code, if you have any questions please let me know below!


  1. Mariano Rodriguez

    Ok this is a great procedure, and thanks for it, but what if you have done everything and the code is still coming up?

    1. John Huh (Post author)

      Hi Mario, thanks for reading.

      so if you have check your IAC and this code is still a problem, you will need to check the continuity between the IAC and the ECU. This will vary of course depending on the ECU and model of your Civic. Have you tried to replace the IAC yet? Do you feel it buzzing or working at idle? if you cannot, try bypassing the coolant lines that run to the idle air controller. This will cause the Civic IAC to become noisy, and it’s a quick and dirty way to determine whether or not the IAC is still working.

      Try these steps and let me know how it turns out. Thanks for commenting!

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