The 2003 Ford Fiesta's computer keeps track of all electrical and mechanical functions of the vehicle. It will alert you to any service that needs to be done or any system malfunctions. It does this via warning and service lights that illuminate on the vehicle's instrument panel. Once repairs or service have been completed, you will need to reset the computer in order to shut of these lights and to keep the computer functioning properly.
Pull the bonnet release to open the bonnet. Prop it up with a rod and locate the battery under the bonnet.
Find the negative battery terminal. You will see a clamp with a nut on it. Loosen the nut with an adjustable wrench and slid the clamp off of the battery terminal.
Wrap a towel around the negative battery clamp and keep it away from the battery altogether. The towel will help to protect you and the battery.
Let the vehicle sit for about 15 minutes. This will allow the computer to reset and erase all trouble codes.
Discard the towel and put the negative battery clamp back onto the negative battery terminal. Tighten the nut with the wrench. Tuck the rod away and lower the bonnet of the car.
Put the key into the ignition and start the engine. Verify that all service and warning lights have turned off.