HOLDEN GEN III V8, Service Training

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GEN III V8 ENGINE MANAGEMENT
VEHICLE SPEED SENSOR
The PCM receives vehicle speed information from the
Vehicle Speed Sensor (VSS) located on the rear of the
transmission. The VSS basically consists of a
magnetic core and a coil. As the output shaft turns, the
teeth on the output shaft concentrate the magnetic
field causing the magnetic flux to increase and then
decrease as the teeth move in and out of the magnetic
field, inducing a voltage into the coil, first, in a positive
and then in a negative direction.
This AC voltage produced in the VSS sensor circuit is
fed into the PCM, the PCM filters and shapes the
signal. The PCM then counts the number of pulses
received in a given time, to determine the vehicle
speed.
Once the PCM has calculated the vehicle speed it
then pulses circuit 123 (Violet/White wire) to earth, this
will cause the 1 2 volts at terminal 1 7 of the
instruments to be pulled down to less than 0.2 volts.
The instrument determines the vehicle speed and the
kilometres from the numbers of pulses it receives. The
PCM also transmits vehicle speed information to other
control modules via the serial data bus normal mode
message.
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