* Automatic Transmission: The speed sensor is typically located on the top or side of the transmission case. It's a relatively small sensor, often with a single wire connector. You'll likely need to get under the car to access it.
* Manual Transmission: With a manual transmission, the speed sensor is usually located on the transmission output shaft, near where the driveshaft connects. Again, this requires working underneath the vehicle.
To be certain: It's highly recommended to consult a repair manual specific to your 2003 Chevrolet Impala's year, make, model, and *transmission type* (automatic or manual). A diagram will pinpoint the exact location. These manuals are often available online or at auto parts stores. Incorrect identification could lead to unnecessary work or damage.
