P0508 IAC valve sense circuit low.
If you encounter a problem with P0508 IAC valve sense circuit low on a Chrysler vehicle, here’s how to proceed. The Idle Air Control is a linear solenoid valve that opens based on computer commands to bypass air around the closed throttle plate that occurs at idle. The IAC has a tapered pintle with a corresponding seat in the throttle body. The PCM constantly check return voltage from the IAC to determine if its working and it compares actual RPM with commanded RPM. If the PCM doesn’t see the correct or expected return voltage, it sets a P0508 IAC valve sense circuit low trouble code.
The computer uses the throttle position sensor, crank position sensor, coolant temp sensor, manifold absolute sensor and switch conditions like; brake, transmission range selector, and A/C to determine the preferred idle speed. Then it commands the IAC to open or close. During off throttle driving, the IAC is closed, except during rapid deceleration where it opens slightly to act as a dashpot to slowly bring down the idle speed and prevent stalling.
Test the IAC
In order to test the IAC, you must have battery voltage above 10-volts with the engine running. You’ll need a digital voltmeter and an ammeter. Start the engine and check to see that it idles at 800-1,500 RPM depending on engine temperature. Then conduct a current draw test on the gray/red wire going to the IAC. Current must be less than 146mA. If the current meets the spec, turn off the engine and test for resistance value across the IAC terminals. Resistance should be 8.7-19.7ohms. If it isn’t, replace the IAC.
If you don’t see current going to the IAC, disconnect the electrical connector at the PCM and check for continuity going to the IAC connector. Next check for voltage right at the PCM IAC terminal. If you don’t see voltage, replace the PCM. A shorted IAC can damage the drivers in the PCM and that can also set a P0508 IAC valve sense circuit low trouble code. Reconnect the connector and check for a short to ground condition between the IAC wires.Posted on by Rick Muscoplat