Speedometer And Tachometer

The input information for the speedometer and tachometer is supplied over the Class 2 serial data link by the Powertrain Control Module (PCM) for the 4 cylinder (L61) engine, and by the Body Control Module (BCM) on the V6 (L81) engine.
The BCM gets the vehicle speed data and engine speed data from the V6 (L81) Engine Control Module (ECM) via the CAN serial data link.