SL1- Code U1300

My wife's 01' SL1 SOHC 1.9 is showing a "U1300 Class 2 short to ground"...does anyone have any idea what sets this code off? I've been having some stalling and starting problems from it. The starter and battery are both ok because the engine is always turning over and I have full electrical power...problem is more apparent when there's a load such as the A/C at idle speeds, causing the engine to drop in RPMs dramatically. Thanks in advance for any help!