In this article, I'll show you how to test the transmission shift solenoids (specifically 1-2 solenoid and 2-3 solenoid) on your GM 4.3L, 5.0L, 5.7L pick up, van, SUV. You'll be surprised just how easy it is to diagnose these shift solenoids when they have failed.epending on the type of scan tool you're using (either a generic scan tool or a professional level technician's scan tool), these two solenoids will be called shift solenoid A and shift solenoid B or 1-2 shift solenoid and 2-3 shift solenoid. To avoid any confusion with what name is used to identify them: