Immobilizer System

The immobilizer system prevents the vehicle from being used if a non Volvo original key for that vehicle is used to start the vehicle. The identity of the remote key is checked electronically when to ensure that the correct remote key is inserted in the Start control module (SCU). On cars with the keyless system it is checked by the keyless vehicle module (KVM). If the remote key is not approved, the steering column lock will not be unlocked and the engine will not start. The customer will not notice the function of the system as long as a valid remote key is used and no fault occurs.

Deactivation and start (only cars without the keyless locking system)

Fig 1: Immobilizer System Communication Diagram

Courtesy of VOLVO CARS CORPORATION

To deactivate the immobilizer system, the remote key must be inserted in the Start control module (SCU) (3/132). When the remote key is inserted in the Start control module (SCU), the Central electronic module (CEM) (4/56) transmits the command to the Start control module (SCU) that the remote key identity must be checked. The Start control module (SCU) activates the antenna and reads off the identity code from the remote key's transponder. This code is transmitted to the Central electronic module (CEM) and compared with the codes that are programmed in the Central electronic module (CEM). If the read off code from the remote key is in the Central electronic module (CEM), the key is approved.

Central electronic module (CEM) will then activate voltage supply to the fuel pump module (PEM).

The central electronic module (CEM), after approval of the remote key, checks the signals on the CAN network regarding the vehicle speed and engine status. If the vehicle is stationary and the engine is not idling, the Central electronic module (CEM) transmits a signal to the Driver information module (DIM) (5/1) indicating that the power supply to the Steering column lock module (SCL) (4/102) must be activated. The Driver information module (DIM) also checks the signals for the engine status and the vehicle's speed on the CAN network. If the Driver information module (DIM) concludes that the engine is not running and the vehicle is stationary, the Driver information module (DIM) transmits a signal that activates a relay in the Central electronic module (CEM). The power is forwarded to the Steering column lock module (SCL) via this relay. The Driver information module (DIM) also transmits an acknowledgment via CAN to the Central electronic module (CEM) that the power supply has been activated. If the starter button has been pushed and the remote key is approved, the central electronic module (CEM) transmits a command to the steering column lock module (SCL) to unlock the steering column lock. The vehicle cannot be started before the spring bolt in the steering column lock module (SCL) is in the unlocked position. The position of the spring bolt is indicated by a contact breaker in the Steering column lock module (SCL) and is connected to the Central electronic module (CEM). A communication check is carried out continuously, whilst driving, between the Central electronic module (CEM) and the Driver information module (DIM) to ensure that the Steering column lock is not activated by mistake while driving. If the central electronic module (CEM) detects that power supply to the steering column lock module (SCL) is too high for any reason while driving, a warning message is displayed in the driver information module (DIM).

When the ignition is switched on or a start attempt is made (by depressing a pedal and pushing the starter button), the communication between the central electronic module (CEM) and engine control module (ECM) is checked. This is to ensure that the correct codes are programmed into both control modules. The engine control module (ECM) also checks the identity of the brake control module (BCM) (4/16) by reading off its serial number. This number is compared with the number programmed into the engine control module (ECM). If these checks are completed satisfactorily, the engine control module (ECM) activates the ignition system. The engine control module (ECM) also transmits a command to the central electronic module (CEM) to allow the fuel pump (FP) to continue to run. If a fault should occur or a check is not approved, the engine control module (ECM) instructs the central electronic module (CEM) to deactivate the fuel pump (FP). The engine control module (ECM) also checks the other parameters covered by the start inhibition function. If all conditions are met, the engine control module (ECM) activates the relay for the starter motor. The engine can then be started.

If any of the above steps should fail, the engine will not start and a message will be displayed in the driver information module (DIM).

The immobilizer system has built-in diagnostic test modes (DTM) to ensure that the engine can be restarted after unintentional stops.

Passive deactivation and start (only cars with the keyless locking system)

Fig 2: Identifying Passive Deactivation

Courtesy of VOLVO CARS CORPORATION

To carry out a start of a keyless vehicle, a pedal must be depressed (clutch (MAN) or brake (AUT)) and the starter button pushed. When the starter button is pushed, an input on the keyless vehicle module (KVM) (4/93) is grounded, which searches for a remote key with passive function in the vehicle. Ground connection from the starter button also goes to the Central electronic module (CEM) (4/56), which, at the same time, transmits an encrypted request to the Keyless vehicle module (KVM). This request is responded to only if an approved passive remote key has been registered. If a remote key is found, the keyless vehicle module (KVM) checks that it is approved. If this is the case, the keyless vehicle module (KVM) transmits a response to the central electronic module (CEM) indicating that the remote key is approved.

If a passive remote key is not registered, the keyless vehicle module (KVM) will transmit a negative response to the central electronic module (CEM). The central electronic module (CEM) will then transmit a request to the start control module (SCU) (3/132) instead to search for a transponder. The central electronic module (CEM) will approve the remote key if a transponder is found.

If a start attempt is made, either on a non keyless or keyless vehicle, the Central electronic module (CEM) checks the signals on CAN regarding the speed and status of the engine. If the vehicle is stationary and the engine is not idling, the Central electronic module (CEM) transmits a signal to the Driver information module (DIM) (5/1) indicating that the power supply to the Steering column lock module (SCL) (4/102) must be activated. The Driver information module (DIM) also checks the signals for the engine status and the vehicle's speed on the CAN network. If the Driver information module (DIM) concludes that the engine is not running and the vehicle is stationary, the Driver information module (DIM) transmits a signal that activates a relay in the Central electronic module (CEM). The power is forwarded to the Steering column lock module (SCL) via this relay. The Driver information module (DIM) also transmits an acknowledgment via CAN to the Central electronic module (CEM) that the power supply has been activated. If the starter button has been pushed and the remote key is approved, the central electronic module (CEM) transmits a command to the steering column lock module (SCL) to unlock the steering column lock. The vehicle cannot be started before the spring bolt in the steering column lock module (SCL) is in the unlocked position. The position of the spring bolt is indicated by a contact breaker in the Steering column lock module (SCL) and is connected to the Central electronic module (CEM). A communication check is carried out continuously, whilst driving, between the Central electronic module (CEM) and the Driver information module (DIM) to ensure that the Steering column lock is not activated by mistake while driving. If the central electronic module (CEM) detects that power supply to the steering column lock module (SCL) is too high for any reason while driving, a warning message is displayed in the driver information module (DIM).

If any of the above steps should fail, the engine will not start and a message will be displayed in the driver information module (DIM).

The immobilizer system has built-in diagnostic test modes (DTM) to ensure that the engine can be restarted after unintentional stops.

Activation

The immobilizer system is activated when the ignition is switched off. The engine cannot be started when the system is activated. The engine control module (ECM) then deactivates the ignition system and the relay for the starter motor. The central electronic module (CEM) deactivates the fuel pump (FP) at the same time. If the driver's door is opened, the Central electronic module (CEM) checks the signals on CAN regarding the engine status and the vehicle speed. If the vehicle is stationary and the engine is off a command is transmitted to the Driver information module (DIM), to activate the power supply to the Steering column lock module (SCL). The Driver information module (DIM) also checks the signals for the engine status and the vehicle's speed on the CAN network. If the Driver information module (DIM) concludes that the engine is not running and the vehicle is stationary, the Driver information module (DIM) transmits a signal that activates a relay in the Central electronic module (CEM). The power is forwarded to the Steering column lock module (SCL) via this relay. The Driver information module (DIM) also transmits an acknowledgment via CAN to the Central electronic module (CEM) that the power supply has been activated. The central electronic module (CEM) then transmits a command to the steering column lock module (SCL) to lock the steering column lock.