GMC Troubleshooting Questions? Ask a Mechanic for Answers
This is normal for the tank to show 1/2 a tank of fuel and die. Since it takes both sensors and calibrate a fuel level for both tanks. If 1 is full and the other empty then it thinks there is 1/2 of the fuel left.
There is no switching valve or switch for switching the tanks. They use a fuel tank control module part number 15061009. The module will sense when the pump needs to run to balance the tanks and run the secondary pump. That pump does not run all the time just to transfer the fuel from one tank to the other.
I cannot find a wiring diagram right now. I will keep looking though.
I can not find a wiring diagram for this vehicle. I did find one for a pickup. It should be close.