Help : what is missing?

[Mogman]

What lights????

 

[GuntherRommel]

trans light im sure for the codes

 

[williamh]

It sounds like it's in limp mode (which means fixed in 2nd gear). This document (link below) has some really good info about how the transmission works and how to troubleshoot it. I'd start by checking the breaker behind the passenger seat. The transmissions is all electronic and the brain is in the box behind the drivers seat. Lack of electical power can cause limp mode (check breaker) or it could be any number of other faults. I'd also check the connection to the transmission box and transmission. Disconnect the negative on the main battery before disconnecting or reconnecting the TCM harness.

https://gear-report.com/wp-content/uploads/2017/03/Supplement_7_4L80E-Transmission_Troubleshooting.pdf

I just had this occur to me. Went for breakfast and when trying to return home. Limp mode , went to test the module and no codes light nada. found breaker behind battery box tripped. So I reset it. No shorts found and the trans has no stored codes. I’m guessing it list stored codes when the breaker tripped.