"Gear D2" on GM 4L60-80E 4 Speed Autos

GM 4 Speed Transmissions use a Pressure Manifold that is linked to the clutches inside the transmission. This manifold sends the signals to the TCM to indicate which gear the transmission is in.

If the COMPUSHIFT Gear parameter is showing D2 (Drive - 2nd gear position), this indicates any of the following situations:

1. The engine is not running
2. The main transmission connector is not connected or seated correctly
3. The fluid pump is not functioning inside the transmission
4. The pressure manifold has a fault

Possible Solutions

1. If the Engine is not running, have the customer start the engine (assuming transmission fluid is in the transmission and the fluid level has been checked) and recheck the Gear Indicator
   
   
2. On the rear/side of the transmission is a round connector that is the Main Transmission Connector. This carries power for the solenoids, signals for the pressure manifold, and signals for the temperature sensors back to the TCM. If this connector is not seated correctly, then the TCM can not control the transmission correctly nor can it detect the correct gear.
   
   It is also possible for this connector to be installed 180° out of phase. This is commonly associated with a Temperature Sensor DTC or a temperature readout that is very wrong. The arrow on the connector needs to be facing out on 4L60 and facing up on 4L80.
   
   4L60 Main Connector
   4L80 Main Connector
   
   
3. If the hydraulic pump inside the transmission is not functioning correctly then this will not be pressurising the fluid sufficiently the engage the pressure manifold or clutches. This may be due to the torque converter not full inserted into the transmission gears or the pump gears have been damaged in some way.
   
   To confirm the pump is not functioning, check the flow through the transmission fluid cooling system. If no flow, the pump is not functioning. This is mechanical issue and needs to be inspected by a suitable automatic transmission specialist
   
   
   
4. If all of the above does note resolve the issue, then most likely the pressure manifold would be in question. Recommend replacing the pressure manifold.
   Here is a youtube video on replacing the pressure manifold.
   https://www.youtube.com/watch?v=i7H2FDNg8Ac&t=369

Beyond this, the vehicle needs to be inspected by an experienced automatic transmission specialist.