* Clearing trouble codes: This is the most common reason. The ECM stores diagnostic trouble codes (DTCs) that indicate problems. Clearing these codes doesn't fix the underlying issue, but it allows you to start fresh and see if new codes appear after driving. You can typically do this in a couple of ways:
* Disconnecting the battery: This is the simplest method. Disconnect the negative (-) battery terminal for at least 15-30 minutes. This will drain the capacitor in the ECM and clear the codes. Reconnect the battery and let the car run for a while to allow the ECM to relearn your driving habits. Important Note: This will also clear any learned adaptive settings (like throttle response), so your car's performance might feel slightly different for a short time.
* Using a scan tool: A scan tool (OBD-II code reader) is a more sophisticated approach. It allows you to not only read the trouble codes but also to specifically clear them. Many inexpensive OBD-II readers are available online or at auto parts stores. This method avoids losing the learned adaptive settings.
* Resetting adaptive learned parameters: The ECM learns your driving style and adjusts parameters accordingly (fuel mixture, idle speed, etc.). If you've made significant changes (e.g., installed a new component, replaced sensors), resetting these adaptations might be beneficial. The battery disconnect method addresses this as a side-effect. However, there’s no specific "reset adaptations" function readily accessible without specialized scan tools.
Important Considerations:
* Check the battery: Before attempting any of these methods, ensure your battery is in good condition. A weak battery can cause erratic behavior and prevent a proper reset.
* Underlying problems: Resetting the ECM only addresses the *symptoms*, not the *cause* of any problem. If you're experiencing issues, the codes should guide you toward the actual problem. Ignoring the underlying issues could lead to further damage.
* Professional help: If you're uncomfortable working on your car's electrical system, it's best to take it to a qualified mechanic.
In summary, disconnecting the battery is the easiest way to achieve what most people refer to as "resetting the ECM" in a 1997 Chrysler LHS. However, using an OBD-II scan tool is preferable for clearing codes without losing adaptive settings and for proper diagnosis.
