Check for Diagnostic Trouble Codes (DTCs) Consult your vehicle’s factory information for specific repair instructions and recommended safety procedures. Note: The following are general guidelines for educational and entertainment purposes only. The latter has single-vehicle subscriptions for DIYers that provide detailed factory repair information. Manuals, such as those from Chilton, are good, but an ALLDATA subscription is even better.
99 ASTRO VAN SIGNS OF BAD ECU DIAGNOSTIC PORT CODE
The problem is, most DIYers don’t have access to an OEM-level scan tool-which is why we’re going to discuss IAC troubleshooting with a code reader and digital multimeter (DMM).īefore beginning, however, you’ll want to have the vehicle’s repair information handy. On many vehicles, you can directly control the IAC, taking the PCM completely out of the loop, by using an OEM-level scan tool. If the IAC does not respond to the scanner’s commands, the issue is either the IAC or its control circuit (excluding the PCM). Idle speed should increase as you incrementally open the valve, and decrease as you close the valve. OEM-level scan tools are awesome because, on many vehicles, you can directly control the IAC, taking the PCM completely out of the loop. Code readers and OBD-II scan tools don’t have the necessary bi-directional controls to test an IAC. OEM-level means the scanner has most of the same functions as the dealer’s factory tool. Without a doubt, using an OEM-level scan tool is the easiest way to test an IAC valve. That’s why it’s a good idea to test a suspect IAC before you rush out and buy a new one. Vacuum leaks and circuit problems can mimic a bad IAC valve. Engine Won’t StartĪlthough rare, there are instances where a faulty IAC can throw off the air/fuel mixture enough to prevent the engine from starting. A faulty IAC can starve the engine of air at idle, resulting in stalling. Your car’s engine needs a precise mixture of air and fuel to run well.
Incorrect Idle SpeedĪs you probably guessed, a faulty IAC can result in an idle speed that’s either too high or too low, depending on whether the device is stuck open or stuck closed.Īn idle speed that bounces up and down is also a possibility. If the module detects a problem with the way the IAC is behaving, it will turn on the check engine light and store a corresponding diagnostic trouble code (DTC) in its memory. Your car’s primary computer, which is often referred to as the powertrain control module (PCM), controls and monitors the IAC.