Speed sensors went away many years ago. You have a computer-controlled transmission that uses an input shaft sensor and an output shaft sensor. The transmission computer uses one sensor, final drive gear ratio, and programmed-in tire size to calculate the expected reading from the other sensor. If they don't agree, slippage is occurring and it defaults to second gear and stays there.
The tire size is used to calculate miles per hour. That information is sent to the body computer above the driver's feet. It in turn sends the information to the instrument cluster. If the transmission is shifting properly, the sensors are working. The transmission computer can cause loss of speedometer and odometer. If the odometer still advances, suspect a problem in the instrument cluster.
Ya gotta love computers. Three to run a speedometer when a cable used to work just fine!
caradiodoc
Mar 21, 2009 at 4:48 AM
