1996 Lumina van has a check engine light on. It's idleing up and down when sitting but when running it seems fine. So I hook up the scanner to check the code and the scanner can't communicate. Try the scanner on my truck and it works fine. Install a new computer and hook up the scanner and still no communication? Try the scanner on my truck and it works fine. What in the heck could cause this? Anyone have any ideas?
Thanks!

 

Possibly a bad connection in your data port?
Loose wires to the port?