POWERTRAIN CONTROL MODULE - VEHICLE SPEED OUTPUT (VSO)
The PCM-VSO (Powertrain Control Module - Vehicle Speed Output) speed signal subsystem generates vehicle speed information for distribution to the vehicle's electrical/electronic modules and subsystems that require vehicle speed data. This subsystem senses the transmission output shaft speed with a sensor. The data is processed by the PCM, and distributed as a hard-wired signal or as a multiplexed data message.
The key features of the PCM-VSO system are to:
- Infer vehicle movement from the output shaft sensor signal
- Convert transmission output shaft rotational information to vehicle speed information
- Compensate for tire size and axle ratio with a programmed calibration variable
- Utilize a transfer case sensor for four wheel drive applications
- Distribute vehicle speed information as a multiplexed message and/or an analog signal
The signal from a non-contact shaft sensor (Output Shaft Sensor--OSS or Transfer Case Shaft Sensor--TCSS) mounted on the transmission (automatics, manuals, or 4X4 transfer cases) is sensed directly by the PCM. The PCM converts the OSS or TCSS information to 8000 pulses per mile, based on a tire and axle ratio conversion factor. This conversion factor is programmed into the PCM at the time the vehicle is assembled and can be reprogrammed in the field for servicing changes in the tire size and axle ratio. The PCM transmits the computed vehicle speed and distance traveled information to all the vehicle speed signal users on the vehicle. VSO information can be transmitted by a hard-wired interface between the vehicle speed signal user and the PCM, or by Speed and Odometer SCP multiplexed data messages.
The VSO hard-wired signal wave form is a DC square wave with a voltage level of 0 to VBAT. Typical output operating range is 2.22Hz per MPH (1.3808 Hz pr 1 Km/h) . Multiplexed data for speed and distance data are transmitted as separate SCP messages over the SCP multiplex link.