This is what I found on Edmunds.com RE: 2003 CelicaWhat's New for 2003
The Celica has been revised for 2003 with freshened front and rear styling. In front, the Celica gets a new bumper and fascia with a wider upper air Intake
. Newly available high-intensity discharge (HID) headlights complement the car's advanced styling, and redesigned rear lights echo the projector-style look. Inside, Toyota has redesigned the center dash cluster for improved legibility and added a standard JBL audio system to the GTS model. A power antenna is now standard on JBL-equipped models. Finally, you can get two new colors: Solar Yellow and Zephyr Blue Metallic.
But I know there were some subtle engine/tranny changes that's not documented.