I've had to do this to three cars in the last year. These vehicles were all in poor state of repair so I will make a broad assumption that the cause of this occurence was the use of a cheap and/or poorly made code reader/cable. The symptom is no communication or loss of communication with scanner. The last one wouldn't pass an OBD test for lack of communication. The cause is loose female terminals in the DLC.

I've found that when one is loose, all (16 max) are loose. I use the male Metri Pack 150 terminal in my test leads kit to do a pin drag test and if it fails...

Pop out the DLC connector from the dash stay for some working room, remove the connector lock and remove one terminal at a time. On the opposite side of the 'stabilizer wings' (for lack of better term) there will be a square hole in the terminal. If you gently push a pick tool straight through this hole you will put tension on the spring loaded wiper portion that is supposed to generate loaded tension on the male terminal. I find that these often give a faint 'click' feedback noise as they pop back into position, but some do not. At any rate, I have been 100% successful at restoring proper pin drag with the Metri Pack 150 test terminal and full scantool connectivity with this method. Given that the spring can withstand many test insert/removals, I feel that a poorly made test connector or ham fisted use has spread the springs past the point where they bind on something internal to the terminal. They need to be popped past that point to function again.

Tony from Missouri