error codes for ABS/Traction control

My ABS and Trac off lights are always on and I am suspecting one of the sensors to be at fault. Weird enough, sometimes, very rarely, only the trac off light will stay on, and the ABS will stay off. But almost always, when i start the engine, both lights stay on.

Another weird thing, is that if i start the engine with my foot on the brake pedal, none of them turn on, and i can turn on/off the traction control. However, as soon as I (fully) take my foot off the brake pedal, they both come on.

Could someone please tell me how to get some error codes out of this? (without going to a mechanic?) I'm new to this, so I need some details on how/where things are.

97 Park Avenue non-supercharged 232,000 km

thank you!