The VSS provides an indication of road speed to the ECM/PCM. The sender is either a electronic Hall switch or an inductive type, which sends pulses directly or via the dashboard circuit to the ECM/PCM.

If the ECM/PCM receives no pulses from the VSS input, a fault, Code 24 will be set in the ECM/PCM. This will result in increased fuel consumption, poor idle quality or stalling can be experienced. Vehicles fitted with TH700 automatic transmissions will have no torque converter clutch lockup.

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

• The ECM will shut off the fuel during deceleration. The VSS must be operating correctly for this to occur.
• The ECM 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.
• The Commodore automatic transmission has an in-built torque converter clutch, which reduces the efficiency loss of the automatic transmission by manually coupling the input shaft to the engine, under certain load conditions. These conditions are met when the engine coolant temperature is above 42°C, the vehicle speed is above 72 Kph, and the throttle is open. Without a vehicle speed reference this function is not possible.

When adapting the TH700 GM transmission to a four wheel drive transfer case the extension housing is replaced by an adaptor housing.

The original GM VSS is removed with the rear extension housing.

Marks 4WD Adaptors have overcome this problem by designing VSS interface module. The module is wired into original Hilux/4Runner speedometer VSS. The output from the module is then connected to the GM ECM. The speedometer still functions normally.

The Toyota Land Cruiser, Hilux/4Runner VSS (Hall Effect Type) sends pulses to the pre programmed module, which interprets them for the ECM.

The ECM is tricked into believing the engine is still fitted to a Commodore allowing the ECM to function as normal.

Marks 4WD Adaptors have built into the module, a self test circuit. A green LED light fitted to the module flashes when the module is sending pulses to the ECM.

The unit is very easy to install and only requires four wires to be connected. The unit is supplied with all necessary mounting hardware and full instructions.