P0505 Code: Meaning, Symptoms, Causes, Diagnostics, And Fixes

The P0505 OBD2 code triggers when there is an issue with your idle air control system. Since this system is responsible for the speed of your idle, it won’t affect your vehicle while it’s driving. It can lead to stalling and rough idling, however, so you’ll notice something’s amiss when this code activates.

Most of the time, the diagnosis of a P0505 is simple and straightforward. In many instances, a faulty IAC valve or sensor is to blame. This trouble code can also be triggered by other issues, though, including bad wiring and vacuum leaks. Read on below to find out how you can identify the true root of the issue. 

P0505 Code Definition

P0505 Code Definition (Generic): IAC (Idle Air Control) System Malfunction

P0505 BMW Code Definition: (IAC) Circuit fault

P0505 Dodge Code Definition: IAC RPM Lower than Expected

P0505 Ford Code Definition: (IAC) circuit fault

P0505 Jeep Code Definition: Idle Control System

P0505 Nissan Code Definition: (IAC) circuit fault

P0505 Toyota Code Definition: Idle Air Control System

What Does P0505 Mean?

The idle air control (IAC) valve affects the idling speed of your engine. The throttle plate closes when your vehicle is idling. The powertrain control module (PCM) or engine control module (ECM) controls the IAC, limiting how much air can get around the throttle plate. 

There is a shutter or plunger on the IAC valve that controls the airflow. When it opens, more air can get through, and the engine idles higher. When it closes, there’s less air, and the engine idle speed lowers. 

To determine the engine idle speed, the ECM or PCM monitors the IAC valve circuits. The voltage varies depending on how much the valve is open. When the engine’s computer detects a voltage that is out of sync with the demands of the engine, the P0505 trouble code is triggered.

In most vehicles, the IAC valve and monitor are mounted on or near the intake manifold throttle body. 

The sensor monitoring the IAC valve varies in design depending on your make and model. The specific repair steps for this trouble code can also vary, so be sure you check your vehicle’s manual before starting your diagnosis. 

What Are The Symptoms Of The P0505 Code?

  • Activation of the check engine light
  • Low or high engine idle speed
  • Rough idle or stalling while idling
  • Intermittent stalls when releasing the throttle
  • Engine won’t idle unless throttle is depressed
  • Reduced gas mileage (if caused by vacuum leak)

What Are The Causes Of P0505?

  • Damage to IAC connector
  • Open or short in IAC circuit
  • Clogged or sticking IAC valve
  • Clogged or restricted IAC passages
  • Vacuum leak in the intake system
  • Faulty IAC
  • Faulty PCM or ECM

How Serious Is The P0505 Code?

The P0505 code is of moderate severity. Your engine may stall and idle rough while this code is active, which could cause engine damage if allowed to continue long term. You can safely drive your car for a short while, but you should repair the problem as soon as possible. 

How To Diagnose And Fix The P0505 Code?

Tools you’ll need:

Use an OBD2 scan tool to diagnose the P0505 code.
The P0505 code can be diagnosed by OBD2 scanner
  1. Use an OBD2 scan tool to check for other OBD2 codes, then clear the codes and test drive your vehicle to see if the P0505 trouble code returns.
  2. Monitor the engine idle data while conducting a road test. Check to see if the engine is staying in gear when driving.
  3. Visually inspect the vacuum hoses around the throttle and intake manifold for leaks. Pay close attention to the ends of hoses, and be sure to feel along with any hidden areas for damage or holes.
  4. Inspect the gaskets on the intake manifold and surrounding hoses. Replace any that are cracked or damaged, and ensure they are all firmly connected.
  5. Check for carbon build up on the IAC valve and throttle plates. Clean any that you find with throttle body cleaner. 
  6. Remove the IAC and check for any build-up or other blockages in the passages. Clear any that you find. Throttle body cleaner will work to remove carbon blockages here, as well.
  7. With the IAC still unplugged, start your engine. Don’t be alarmed if other IAC codes trigger when you do this. Clear the codes, then see if the P0505 code returns. If it doesn’t, there is an internal short in the IAC circuits and the unit should be replaced. If it does, continue with step 7.
  8. Visually inspect the wiring harness and wires. Check for the continuity of all signal lines. Replace any that are damaged or corroded. Also, ensure none of the wires are rubbing each other or causing each other to short. 
  9. If you can’t see any damage to the wiring but the code will not clear, you may want to check the voltage of the wires with a digital multimeter. They should not offer any resistance when they’re unplugged from the IAC. Replace any that do register a voltage.
  10. Should the code still not clear, you may have a more serious issue with your engine computer. Take your vehicle to a mechanic for further diagnosis. 
The way to fix the P0505 code.

Common Mistakes To Avoid While Diagnosing The P0505 Code

Some mechanics assume the IAC valve or sensor is the issue before checking for other problems. This won’t fix the problem if it’s caused by carbon build-up or vacuum leaks, however. Make sure you conduct a thorough diagnosis before replacing any components. 

Tips To Avoid Po505 In The Future

Carbon build-up on the IAC valve or in the passages can often trigger the P0505 trouble code. Some carbon is common after the car has been running for a few years. You can help prevent excessive carbon build-up by keeping up with your scheduled maintenance, ensuring all fluids in your engine are clean, at the right level, and of the right viscosity for your vehicle.

Read more: OBD2 Codes: Full List Meaning & Fix Guide

Tim MillerFounderOBD Advisor

I’m Tim Miller from Denver, Colorado. I’m the founder of obdadvisor.com, an automotive blog about "Diagnostic Tools and Auto Repair". My fan page is facebook.com/autozikcom. I've been working as an automotive mechanic and blogger for over 10 years writing articles to share my experiences and expertise.

Web: https://www.obdadvisor.comEmail: [email protected]
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