If your vehicle has an Allison automatic transmission, certain transmission malfunctions will turn this light on.

This light is located with the auxiliary warning lights in the center of the instrument panel.

If this light comes on while you are driving, do not use the transmission shift control. Using the transmission shift control may result in the loss of forward gears. The computer for the transmission senses a problem and chooses a gear to stay in so that you can drive the vehicle in that gear. You may not be able to drive as fast or back up when this light is on.

Notice: If the service transmission warning light comes on while you are driving, it is a warning that making a transmission "range" change could leave you stranded. The vehicle may not continue to move if you change gears with the transmission shift control. The transmission can't operate in all gears because something is wrong. Leave the shift control alone, and drive directly to a qualified dealer for service. If you can't go in for service immediately, have the vehicle towed.