Automotive technology has evolved in such a way that your vehicle’s computer can tell you when there is something wrong with your car. In trucks and other larger vehicles, the overdrive light on the dash is like the warning light for your transmission. If the overdrive light is on, but does not flash, that means you've deactivated the overdrive feature of the transmission.
The button to activate or deactivate overdrive is commonly found on the end of the gear shifter on vehicles equipped with a column shifter, or on the end of your wiper control switch on vehicles equipped with a console shifter.
When the computer detects a problem with any transmission component or a problem in the transmission’s electronic control system, it will flash the overdrive light and store trouble codes in the car's computer. Have the computer scanned by a scanner that reads more than the federally mandated emissions codes, to determine what is at fault.
Even if your vehicle seems to shift fine, continued driving without addressing the indicated transmission problem may result in additional damage or complete failure of the transmission.