Before engine work (new head gaskets, intake gaskets) I had no problems connecting my OBD scanner to the vehicle. A week after the engine work the check engine light came on, so I was going to read the codes. The software said it couldn't connect, but it had good wifi signal, connected to the iPad and I could see the lights flashing as the app tried to connect to the scanner. I thought it was a defective scanner so I purchase an additional one, but with the same results. Tried the scanner on wife's car (should have done this before buying a new scanner) and no problems connecting. Have tried several different apps all with the same results. Looks like it is reading the data from the engine computer and at the last minute all apps say lost connection. Engine is a 2004 5.3 in a Tahoe. Any ideas on why the Tahoe computer doesn't want to communicate?

Sorry for the second post, orginally posted in the Tahoe forum, but received no reply's and I should have posted here in the first place.

 

if the scan tool won't power up...check the cig fuse
if the scan tool will power up but won't communicate...check the power and grd to the module that is offline.
Can you communicate with anymodule? Is you scan tool capable of communication with modules other than the pcm?

 

The scan tool powers up, I can connect with wifi. The programs i have tried are all IOS apps, OBD Fusion, Auto Doctor and EOBD-Facile. They all say something along the lines that "timed out" or "lost connection".

How would I go about checking the power and ground to the modules?

thanks