The vehicle speed sensor in your Altima provides a signal to the on-board computer that indicates actual vehicle speed from the output shaft of the transmission. This signal is used by both the engine computer and the anti-lock brakes computer to calculate the functions like proper transmission gear, engine load, wheel lock-up and even speedometer readings. The average home mechanic can complete this project in a couple of hours in most cases.
Disconnect the negative battery cable from the battery using a 10 mm wrench to loosen the cable end and then twist as you pull the cable off the battery. The battery in the Nissan Altima is located on the driver-side of the engine compartment in front of the air filter housing.
Remove the electrical connector from the speed sensor located on the driver-side of the transmission near the firewall. Remove the 10 mm bolt that attaches the sensor to the transmission using a socket, ratchet and long extension. Twist the sensor as you pull it from the transmission.
Compare the gear on the end of the new sensor with the gear on the end of the old sensor. They should be the same color and shape. Insert the new sensor into the transmission and push it down as you twist it until it seats completely in the transmission. Rotate the sensor to line up the mounting hole and install the 10 mm bolt. Tighten the bolt securely and plug the electrical connector into the new sensor.
Reinstall the negative battery cable and start the engine. Test drive the Altima to verify the speedometer functions and the check engine light is off.
