Vehicle Security System

NOTE: DO NOT keep more than one ignition key, keys from other vehicles, or gas station speed payment devices on the same key ring with the ignition key. The engine may not start. TestBook/T4 is necessary to interface with vehicle security system.

Basic Operation - The vehicle security system is very sophisticated. If vehicle is not serviced (repaired) properly, vehicle will not start. The vehicle security system Electronic Control Unit (ECU) operates in a secure interface which cannot be by-passed or copied. Vehicle starting begins through a transponder in the vehicle key which is energized by a transponder coil surrounding the ignition switch. When the ignition is turned to AUX (position one), the transponder data is read by the vehicle security system (ECU) which will validate the start request.

The vehicle security system (ECU) receives information from related vehicle systems and passes a coded signal to the Engine Control Module (ECM). If all starting parameters have been met, the information is decoded by the ECM which will allow the engine to start. The information (coded signal) is on a rolling code system. If either component is replaced, both the ECU and the ECM will require synchronization before vehicle will start.

Ignition Key - The key head contains the transponder. If a key is lost, the lost key can be disabled (not allowing vehicle start) using TestBook/T4. If a lost key is found, it can be enabled (allowing vehicle start) using TestBook/T4. The vehicle security system (ECU) is programmed with data to support up to ten keys. The programmed information is recorded against the Vehicle Identification Number (VIN) for the vehicle and stored in a database. Replacement or spare keys are delivered to the dealer programmed with the correct information specific to the particular vehicle and ready for use. The vehicle security system (ECU) is programmed during manufacturing with data to support up to ten keys. The transponder transmits three separate pieces of information to the vehicle security system (ECU):

Unique key identification number which is passed to the ECU.
Unique key password used by the vehicle security system (ECU) to communicate with the transponder.
Confirmation that the rolling code from the transponder is correct to the rolling code stored by the vehicle security system (ECU).

Vehicle Security System (ECU) Programming - The vehicle security system (ECU) is programmed with vehicle specific data during manufacturing. Vehicle security system (ECUs) are only available from an authorized dealer. If a replacement vehicle security system (ECU) is required, it will be ordered and delivered to the dealer programmed with the original information stored during manufacturing. The ECM will not require reprogramming because the replacement vehicle security system (ECU) will have the same identification code as before. The ECM and the vehicle security system ECU will need have their rolling code synchronized using TestBook/T4. Follow manufacturers instructions for programming vehicle security system (ECU).

Engine Control Module (ECM) Programming - If the ECM is replaced, the ECM will have to learn the vehicle security system identification code. This is accomplished using TestBook/T4. When the vehicle security system (ECU) receives the correct diagnostic message from the TestBook/T4, it will transmit the identification code on a continual basis until the ignition is switched off. Simultaneously, the ECM is also receives a diagnostic command to learn the new code. Follow manufacturers instructions for programming ECM to operate with the vehicle security system (ECU).

Remote Transmitter (Handset) Synchronization - If the handset fails to lock or unlock the car, this may be because the coded signal transmitted by the handset, and the signal expected by the vehicle security system (ECU) are no longer synchronized. To resynchronize the remote transmitter, position remote transmitter in close proximity to vehicle. Operate either button of the transmitter at least five times in quick succession. Synchronization is complete.