* Resetting the PCM (Powertrain Control Module): This is the main computer controlling the engine and transmission. There's no "reset" button. Instead, disconnecting the battery's negative terminal for about 30-60 minutes will usually clear the PCM's memory. This is often done to address minor glitches or after installing a new part. Caution: This will clear any radio presets and possibly other personalized settings.
* Resetting the Check Engine Light (CEL): Disconnecting the battery as described above *might* clear a CEL, but only if the problem causing it was a temporary glitch. If the CEL is on due to a persistent problem, disconnecting the battery won't fix the underlying issue. You'll need to diagnose and repair the problem to get rid of the light. An OBD-II code reader can help identify the problem.
* Resetting other modules: The Ranger might have other modules (like for the airbag system or body control) that have their own procedures for resetting, if needed. This is less common for a '99 model, though.
* Clearing trouble codes: This requires an OBD-II code reader. The reader will display the trouble codes, and you can then use it to clear them after addressing the problem.
Before disconnecting the battery:
* Turn off the vehicle completely.
* If you have a security system, you might need its code to re-arm it.
* Consult your owner's manual. While it may not explicitly say "reset the computer," it might offer relevant information about battery disconnections.
In short: For most common issues, disconnecting the negative battery terminal for about an hour is the closest equivalent to a "computer reset" for your 1999 Ford Ranger. But if you're trying to fix a specific problem, you need to diagnose the cause first. A mechanic or a diagnostic tool is recommended for more complex situations.
