P0740 p0753 p0758 p0785 p1860
 

Ok here it is, 2004 trailblazer 4.2 4x4. Had the 5 error codes, changed out ignition switch first off since I had a spare one in my envoy. Test drive no power engine light back on, rescanned same 5 codes
tested fuse 47 key on good both sides. Tested pink wire at trans connector and noticed I have fluctuating voltage with key on test. Every time I moved the harness I got a different readings from 3V to 12.3 V.






Would it be safe to assume the external harness needs to be replaced on the tranny.


Any Ideas out there?
thanks

"External harness" includes most of the underhood wiring, big job and big money. Might want to trace it back to find the poor connection & repair it. If you can't find it, try running a jumper wire to bypass the known bad area. The pink wire goes to the ignition module and ignition coil, they both have battery voltage with the ignition in the RUN position.

you can buy a new exterior harness with trans connector, it has a lot of extra wire. I am thinking problem is may be in the connector itself.


I am going to try to test the pink wire before the connection. I will be doing that when pouring rain stops

I had all the same codes pop up last week, and this was after replacing my ignition switch about six weeks ago. Traced what wires I could, tested fuses, nothing. Finally just replaced the ignition switch again (thank you warranty) and it's running perfect again. Not sure it will help but thought I'd share. Good luck, this can be a nightmare....