N14 sensor location

[Jas2153]

Can somebody tell me where the speed sensor is located on a N14? When I'm watching the telematics on an app while the truck is in motion, it will show that the truck is idling. Sometimes it does work and show the correct mph and direction of travel. There are times when the truck is idling while parked and the telematics will show that it is in motion. The fault code that shows is PID-84 Road Speed. This code comes and goes. Is it the speed sensor that is associated with this code. I realize it could also be the wiring, I'm just trying to see where to start first.