if I disconnect battery leads will that erase scanner codes? 2003 vue 2.2 L

The codes will probably be erased but the problem will still be there , you can check for spark by grounding out the plug wire on the block , what problem are you having ?:

only sensors that can prevent spark are cam or crank, most other sensors are ignored during startup. BTW if you do ground plug to check for spark watch where you hold it, you can get a nice little shock otherwise.