Error Code P0508 is defined as Idle Air Control Circuit Low. This means the idle air control system circuit is too low, which is seen as an inconsistency in the engine’s RPM idle.
This code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system and made in 1996 up to present. It’s common among Chrysler, Dodge, Hyundai, Mazda, and Jeep. Specifications on the definition, troubleshooting, and repairs, of course, vary from the vehicle’s make and model to another.
This code means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has detected a problem in the vehicle’s IAC (intake idle air control) circuit, which in this case is a value that is lower than expected.
Whenever there’s an inconsistency in the engine’s idle RPM, be it too high or too low, the PCM will try to correct the RPM problem. If it’s unable to solve the problem, then it will store the code.
Other related error codes include:
- Error Code P0509 Idle Air Control System Circuit High
- Error Code P0511 Idle Air Control Circuit
- Error Code P0518 Idle Air Control Circuit Intermittent
- Error Code P0519 Idle Air Control System Performance
As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other possible symptoms include:
- Low or high engine idle RPM
- Engine stalls at low speed or when the accelerator is not depressed
- Engine stalls when the throttle is released
- Unusual noises from the throttle body areas
In some cases, other IAC related codes may be present.
Common causes for this code include:
- Open or shorted IAC motor harness
- bad electrical connection in IAC due to the motor circuit
- Faulty IAC
- Dirty throttle body bore
How to Check
To diagnose this code, connect an OBD-II scanner to the vehicle’s computer system. Check whether there are other codes present, take note of the data, and then reset the codes. Test-drive the vehicle to see if the code returns. If the code returns, then start to look at the possible causes, such as the IAC.
Check the throttle body bore. Make sure you clean it. Then, reset and then see if the code comes back on your test drive.
Clean the electrical connections and circuits in the IAC to make sure it’s working properly. Repair or replace connections as needed, such as burnt, corroded, or damaged electrical connectors.
Check the engine for vacuum leaks that might be contributing to uncontrollable engine RPM. Repair vacuum leaks and recheck the system.
In many cases, you may need to replace the IAC.
Or replace the PCM, but it’s extremely rare.
How to Fix
Depending on your diagnosis, common repairs include:
- Repair or replacement of damaged electrical connectors at the IAC system
- Repair of vacuum leaks
- Replacement of the IAC
- Replacement of PCM (rare)
Make sure you consult with the vehicle’s information source for the recommended method of testing the IAC motor with the DVOM. If your findings don’t comply with the manufacturer’s specifications, then the common repair is to replace the IAC motor or valve.