The check engine light is on because the ECU (computer) has detected a problem with the emissions system. Have the ECU scanned with an OBD2 scanner to retrieve the code that has been set. This code will help you determine what the problem is.
changed battery engine light stays on
The 2003 Ford Focus has an inline 4 engine.
When the light comes on it's telling you to read the engine diagnostic codes.
Have vehicle scanned to determine the problem
You need to have it checked for codes. The light comes on when the engine computer detects a malfunction.
The engine number of a Ford focus 2003 zx5 is located on the sideways of the engine.
The 2003 Ford Focus has a 2.0 L base engine size.
The 2003 Ford Focus's engine produces 130 hp @ 5300 rpm.
Check your fluid levels.
The 2003 Ford Focus's engine produces 135 ft-lbs. @ 4500 rpm.
Service required is the oil change reminder. Service engine soon would be the check engine light.
In a 2003 Ford Focus : The engine coolant reservoir is on the passenger side of the engine compartment ( it has a thread on pressure cap )