Immobilizer notes
A level 2 or level 2b drive authorization system (DAS) can be optionally installed in model 638 vehicles. The immobilizer prevents the engine from being started by unauthorized persons. After the drive authorization system has been activated, the DSV engine control module interrupts the fuel supply to the injection pump. The data transfer between the DSV engine control module and the DAS control module takes place using a CAN data bus.
DSV engine control module
The DSV engine control module is mounted directly onto the injection pump and essentially consists of a solenoid valve (shutoff valve) and a microprocessor-controlled monitoring system:
When opened, the shutoff valve releases the fuel supply to the injection pump. When closed, the shutoff valve interrupts the fuel supply to the injection pump.
The microprocessor-controlled monitoring system only switches the shutoff valve to "open" when start authorization has been received.
Fail-safe mechanism
The fuel shutoff valve is only closed by term. 15 deactivation. This ensures that the engine continues to run until the ignition is switched off, even if the engine control module is faulty.
If short-term voltage drops occur at term. 15 whilst the engine is running (< 3 sec.), the fuel shutoff valve will be closed but the monitoring system will not change the status. Start authorization still exists. This means that when the voltage returns at term. 15, the fuel shutoff valve opens again immediately and the engine continues to run.
S82.57-0005-01
The adjacent diagram shows the fuel shutoff valve behavior and status changes during short-term power supply interruptions and after an engine stop request.
DSV Fuel shutoff valve open or closed
Term.15 DSV power supply
Status Start authorization "YES" or "NO"
T1, T2 Short-term power supply interruptions at term. 15 (T1, T2 < TD)
TA Duration of identification
TD Engine stop request (ignition OFF > 3sec.)
Anti-theft function
The anti-theft function essentially only allows the engine to run after correct start authorization has been received. Start authorization is given by means of an identification procedure between the DSV engine control module and the radio frequency locking control module. Both control modules are interconnected via a CAN data bus.
Positive start authorization is only given if the following conditions are met after the ignition is switched on:
Vehicle previously unlocked using radio frequency locking system. Monitoring lamp on instrument cluster goes off after pre-glow period.
DSV engine control module and radio frequency locking control module fit together.
Engine start request
The DSV engine control module detects a start request via term. 15. This means that the engine control module receives an engine start request after the ignition is switched on. The DSV reacts to an engine start request by initiating the identification procedure with the RFL in order to ascertain whether the start authorization conditions have been met. The fuel shutoff valve is not set up "open" and thus engine operation enabled until the identification procedure has been successfully completed.