hi there i have a 2003 chevy s10 2.2 motor automatic truck i have only had this truck for 2 months my brother changed the heater core about 2 weeks ago after putting everything back together the security light came on and is on 24/7 the truck will start up then shut's right back down we had a code reader on it but the only code that come up is u1000 which i understand is a communications code we have tried the relearn tricks but haven't had an luck the only thing that somewhat works is to unplug the positive battery terminal and the ecm fuse for 5 min hook everything back up it will then start up and run but as soon as i shut the truck down it goes right back to not wanting to start might there be someone that might be able to give any help or may have any ideas on what might be going on?