From the Wiring Manual:
Vehicle Speed Functional Overview
The hybrid vehicle uses three methods to calculate vehicle speed. The PCM (Powertrain Control Module) uses the ABS signal if available, and will substitute the motor speed if the ABS signal is missing. The PCM will use the engine and generator speed calculation if both the ABS and motor speeds are unavailable.
1. Vehicle Speed From The Anti-Lock Brake System (ABS) Module
The ABS module calculates wheel speed from the front two wheel speed sensors and sends this information to the PCM through the communication network.
2. Vehicle Speed From The TCM (Transmission Control Module)
The TCM calculates traction motor speed from the traction motor resolvers and combines it with (PCM stored) tire size and axle ratio data to determine vehicle speed. This calculation is then sent to the PCM over the communication network.
3. Vehicle Speed From Engine And Generator Speed
The TCM calculates generator speed from the generator resolvers and sends this information to the PCM. The PCM combines input information from the generator speed and engine speed along with tire size and gear ratio to calculate a vehicle speed.
The PCM strategy cross checks all the inputs to determine if they agree with one another.
From the Workshop Manual.
This was describing the GPS signal loss and the ABS message to the AIPM (SYNC) module.:
Navigation rolling wheel count and direction ABS module. > This message provides for more accurate tracking of the vehicle position when the GPS signal is temporarily unavailable for gear lever position for vehicle direction data for navigation.
To the GPSM:
Navigation rolling wheel count and direction ABS module. > Used to verify the gear lever position for vehicle direction data for navigation.
Navigation - If Equipped
The navigation system guides the user to a pre-entered destination. Map data is read from the map data SD card plugged into the media hub. The APIM calculates route information based on GPS data received by the GPSM. The APIM also uses vehicle speed and transmission gear selected signals received through the network to detect vehicle speed and direction, resulting in more accurate navigation tracking. The navigation display is shown on the FDIM.
The compass heading is derived from the GPS antenna signal. There are no serviceable parts for the compass.
The voice recognition system allows the user to interface with the system without using the touchscreen. A microphone located in the headliner provides a direct input to the APIM.