For the Commodore PCM to function properly it must acquire information from external sensors. One vital input is obtained from the original Vehicle Speed Sender (VSS).

The VSS provides an indication of road speed to the PCM. The sender is an inductive type, which sends pulses directly to the PCM.

If the PCM receives no pulses from the VSS input, a fault, Code will be set in the PCM. This will result in increased fuel consumption, poor idle quality or stalling can be experienced.

The VSS is vital for correct operation of the following functions:

• The PCM will shut off the fuel during deceleration. The VSS must be operating correctly for this to occur.
• The PCM has an in-built memory, it learns the correct amount of fuel to deliver under certain conditions. The VSS plays a vital role in determining when these conditions occur.

In a V6/V8 4L60E 4WD transfer case conversion the VSS must monitor the automatic transmission main output shaft for correct transmission operation. For this reason this VSS cannot be used with a 4L60E.

Some VSS units will not fit directly to transfer cases such as the Landcruiser 40 Series which is fitted with a transmission brake. To move the VSS unit, to position it where it will clear the transmission brake and or the transfer case an extension piece is required. Marks 4WD have manufactured such a unit which is now a stock item. The unit moves the VSS 85mm away from the speedometer cable drive.