How do I clear my ecm from all previous codes

 

Disconnect the negative terminal cable at the battery for 30 minutes, then reconnect the cable! We affectionately call this procedure a battery lobotomy!

 

The best way is to fix whatever caused the codes.

 

If you haven't yet attempted to fix what caused the code, then clearing them may be asking for trouble. The codes are valuable diagnostic tools. Also if you need to get a smog check soon, don't clear the codes or they won't be able to test.