A vehicle won't downshift into first gear when coming to a stop. The most likely cause is:

When a vehicle fails to downshift into first gear while coming to a stop, the most likely cause is a governor that is stuck in the high-speed position. The governor in an automatic transmission is responsible for controlling the transmission shifts based on vehicle speed. When the governor is operating correctly, it regulates the shift points, allowing the transmission to downshift appropriately as the vehicle slows down.

If the governor is stuck in the high-speed position, it will not send the necessary signals to the transmission to allow it to downshift into first gear. This malfunction can prevent the transmission from responding accurately to the driver’s intention to come to a stop, which is crucial for ensuring smooth operation and better control of the vehicle.

In contrast, other potential causes listed would not directly disrupt the ability to downshift into first gear during a stop. Worn bands can contribute to issues like slippage or slipping out of gear completely but are less likely to specifically prevent downshifting to first gear. A defective roller clutch typically affects the ability of the transmission to hold a gear during acceleration rather than impacting downshifting behavior. A defective servo might cause issues with engagement of gears, but is less directly related to the specific failure to downshift to first upon deceleration. Therefore,