Modern vehicles, such as the Ford Explorer Sport Trac, are equipped with complex computer systems that monitor and regulate everything from idle speed to diagnostic-trouble codes. This computer is referred to as a PCM (power-train control module), ECU (engine control unit) or ECM (engine control module). If you want to clear diagnostic trouble codes that produce "Check Engine" lights, and you do not have a scan tool, you can do so by resetting the system's computer.
Turn the Sport Trac's engine off and pull the hood latch to open the bonnet. Locate the battery in the front right corner of the engine compartment.
Turn the nut on the negative battery cable (black) with pliers. Once the nut is loose, grasp the base of the cable and unhook it from the battery. You may have to wiggle the cable back and forth to get it off. Push the cable away from the battery to make sure it does not accidentally touch the battery post.
Leave the negative battery cable unhooked for about 15 minutes. This allows enough time for the backup energy system to drain.
Reattach the negative battery cable. Push the cable onto the battery post. Turn the nut with the pliers to tighten the connection.
After resetting the computer, you will experience erratic idle and rough shifting. According to the Ford Explorer Sport Trac manual, this is normal. When you reset the computer, it's forced to "relearn" the idle speed and shift points. The erratic idle and rough shifting should go away after 15 to 20 minutes of driving. It will not harm your vehicle.