Abstract: The present invention relates to an apparatus and a method for a motor vehicle security system relating to immobilizing and enabling of a fuel pump for a motor vehicle engine. The system comprises data input means for receiving driver verification data, an engine control unit (ECU) including an ECU processor for controlling engine operation, a pump control unit (PCU) including a PCU processor for controlling the fuel pump, the PCU being separate from the ECU and integrally housed with the fuel pump. Communication links permit communication between the data input means and ECU, and between the ECU and PCU. The ECU processor is activated to control the PCU when valid driver verification data is received. The PCU processor is then activated to communicate a challenge code to the ECU. The ECU and PCU processors then compute respectively a first and a second response code associated with the challenge code.