First time posting, Dr. Evil said to find the correct post, and post there, hope this is it.

I have a 2001 silverado 2500hd engine code p1781 poor or lost communication to TCM
( transmission control module ??) Found TSB 01-06-04-020 for this code but could not find information on how to correct this.
Can anyone help me with this?
Sure hate to take it to the dealer ( ouch!! )
Thanks in advance for any help.

mcanfield

 

Have you checked the connections both at the TCM and the back of the transmission?

 

Thanks for the reply.
With your knowledge of this, can you tell me what and where is the TCM. I believe I can find the connection at the back of the tranny ( I hope )
Do I assume you are from Wisconsin? I recently moved from south eastern Wisconsin to here in south western Kentucky, yup! Kentucky, we love it here, great weather and much much lower taxes.

 

The TCM is Transmission Control Module. I see you put another post up.

 

Thanks to all that helped with this, I found with more research that a low battery condition can cause erratic codes. This is what the problem was all along. After finding about the low battery condition , believe or not, the next day I went to start my truck and it would barely turn over. I put it on my charger and got it to start, went to Auto zone for their free battery check, found one battery completely dead the other only 70%.
Changed both batteries with 1000 cranking amps. the code went away and has not returned so far.
Thanks again
mcanfield