Can anyone tell me why any scan tool cant communicate with the ecm. At the start it will begin to read but then says car is not responding. I have tried multiple scanners. Thank you

 

I'm having a similar problem with a friends 89 IROC, it says "No data" most of the time and then every now and again during a session it will start to get a data stream. Per the service manual I checked the harness from the ECM to the ALDL and it is good. The service manual says to replace the ECM after that check is done. But I'm having other codes being set too so I don't know where to go with this problem. Right now I have a remanned ECM to put in but I can't just do it till I check out some other things, just in case something is taking out the ECM.

 

i had the same problem with my tpi swap i swapped tbi for tpi and the serial data wire (which is the wire the scanner uses to communicate)for tbi is in pin e (top row 5th from the right)in the aldl connector but for tpi its in pin m (second row end on the right )all i had to do was switch the wire that was in pin e to pin m and then the scanner worked fine this has been left out of many tpi swap instructions i even replaced the computer before i found this when comparing wiring diagrams try it and let me know