* 1.8T: The 1.8T models came with a 1.8L turbocharged four-cylinder engine that produced 170 horsepower.
* 2.0: The 2.0 models came with a 2.0L four-cylinder engine that produced 115 horsepower.
Therefore, the base engine size for a 2003 VW Passat is either 1.8L or 2.0L, depending on the specific model.