What is typically indicated if an automatic transmission refuses to shift up from low gear?

When an automatic transmission refuses to shift up from low gear, it typically indicates issues related to internal components that control the shifting process. Worn clutch packs or low governor pressure are significant factors in this scenario.

Worn clutch packs can result in inadequate engagement or disengagement of gears, preventing the transmission from smoothly shifting up through the gears. Similarly, low governor pressure, which is the hydraulic pressure regulated by the governor mechanism, is essential for the transmission to know when to shift. If this pressure is low, the transmission may not receive the necessary signals to shift into higher gears.

In contrast, overfilled transmission fluid can lead to foaming and erratic shifting behaviors but does not directly cause a refusal to shift from low gear. Faulty spark plugs would affect engine performance and misfiring, but they wouldn't specifically prevent the transmission from shifting. Excessive tire pressure mainly impacts tire wear and handling but does not influence transmission operation. Thus, the presence of worn clutch packs or inadequate governor pressure is indeed the most relevant explanation for the transmission's inability to shift properly.