The alternator is over or under charging.
You have a broken serpentine belt. Replace it.
Disconnect the battery for about an hour, then hook it back up. If it comes back on, something is wrong.
Bad Alternator or the Battery possibly is losing voltage. I replaced the alternator and serpentine belt before thinking it was the battery. The battery was only 16 months old. But it turned out to be the bad source.
What type of battery do i need for a 2002 ford focus
The check engine light on a 2002 Ford Focus can be reset by disconnecting the battery for 1 to 2 minutes. This resets the vehicle's computer and clears the light.
remove the light assy from the car.
On a 2007 Ford Focus : That is the " upshift " light To maximize fuel economy , when the light comes on shift to the next higher gear
alternator is not charging battery, or loose - corroded connection on battery cables
Your battery isn't being charged or accepting a charge
There is problem with the charging system.
Unhook your negative battery cable, turn your light switch on, then turn it off and reconnect the battery. That should reset the computer.
1g.