Noticed the following yeaterday on a 22 mile return data logging hwy cruise.
Transmission Flags Status:

1. 1st gear is always "FALSE" whether park/neutral is "NO, or "YES"
2. Under 60 mph
   • 3rd gear = "TRUE"
   • 4th gear = "TRUE"
3. Over 65mph
   • 3rd gear = "TRUE"
   • 4th gear = "False"
   • Overdrive request = "YES"

I can't image any condition where these combinations are possible.
Can someone shed some light on this?

 

Didn't list which ECM and maskID is in use. However, with f-body's and the 700R4 only hi-gear status is sent to the ECM. The Park/Neutral is a switch on the shifter. So even with the engine off and key-on the prk/neut indication is sent to the ECM.

Back to 4th gear. This is a pressure switch within the transmission. This switch is either NC or NO, dependent upon the application. So it very well may be that the wrong switch is in the trans (for the app).

Note that most (all?) GM MaskId's have a flag to define which 4th gear switch is in the tranny. So if the opposite is reported by the ALDL, then a flag change will correct it.

Note that this also affects which TCC lock/unlock tables are used within the ECM.

RBob.

 

'165 ECM 6E mask.
Diagram shows TCC relay contacts for 4th gear signal as NC.