years ago, you had an airbag light problem
viewtopic.php?f=18&t=25233" onclick="window.open(this.href);return false; but there was no follow up. What was done then to fix that problem?
http://www.ecutesting.com/c0000_fault_codes.html" onclick="window.open(this.href);return false; says C0000 is " Vehicle Speed Information Circuit Malfunction" Since that list also has codes for individual wheel sensors, it is probably not a single wheel, but perhaps a centralized problem with the ABS controller.
Looks like you have a 2004 Vibe. In 03-08 Vibes with ABS, there are speed sensors on each wheel, they feed the ABS computer, which is part of the chunk of hardware on engine compartment wall on the belt side of the engine. The ABS computer also sends signals that drive the speedometer,as well as the ABS and Brake lights in the instrument cluster. It is easy to spot, has a number of brake lines going to it and one wire bundle. It also is sort of under the refrigerant lines running the the AC heat exchanger in front of the radiator.
What did the garage have to do to fix the AC problem? Is there any chance the garage disconnected or damaged wires running to the ABS controller?
There are also two large ABS fuses in the under hood fuse block, probably worth checking those