Start enable
If the identification data is correct, the CAS control unit activates the starter motor via a relay in the control unit. At the same time, the CAS control unit the CAS control unit sends the DME control unit an encoded enable signal for the engine start. The DME control unit only enables the engine start if a correct enable signal is received from the CAS control unit.
The following test module is performed after insertion of the ignition key in the ignition lock or the remote key in the insertion slot:
- The transponder in the ignition key or in the remote key is supplied with power via the ring aerial and transmits the key data to the electronic immobilizer or CAS control unit.
- The EWS or CAS control unit checks the correctness of the key data and only then enables activation of the starter by the DME/DDE.
- The DME/DDE uses a random number and the secret key to calculate a request. The DME/DDE transmits this request via the CAN data line (PT-CAN and K-CAN) and the body bus (also called CAS bus) to the CAS control unit.
- The CAS control unit uses the request and the secret key to calculate the response. The response is transmitted by the CAS via the CAN data line (PT-CAN and K-CAN) and the body bus (also called CAS bus) to the DME/DDE.
- The DME/DDE itself also calculates the response that the CAS control unit expects. The DME/DDE then checks that the response it receives from the CAS control unit matches the response it has calculated itself. If the responses match, the engine start is enabled.
Identical rolling codes are stored in the control units whose value changes after each starting operation. The rolling code is generated from a random number and the secret key.
Notes for Service department
General notes
Adjustment of engine management system with electronic immobilizer
With the introduction of the new electronic immobilizer (4th generation) the adjustment between engine control unit and electronic immobilizer is no longer applicable.
- 6-cylinder spark ignition engines The deletion of the adjustment starts with the engine control units MSV80 and MSD80 as from 06/2006.
- Diesel engines The deletion of the adjustment starts with the engine control units DDE7 as from 03/2007.
- Engines from M GmbH The deletion of the adjustment starts with the engine control unit MSS60 as from 06/2007.
From this point onwards, certain control units can only be replaced with control units specifically ordered for the respective vehicle.
If the CAS, EWS (only E83) or DME/DDE is defective, a certain procedure must be followed. The required control unit must be ordered to match the vehicle exactly. For this, the vehicle data (vehicle identification number) is required. An EWS adjustment is not necessary after renewing the control unit. > E70 Adjustment is necessary if the electronic transmission control is replaced. For adjustment, the CAS control unit transmits an individual code to the EGS control unit. This individual code is required for the authentication procedure for enabling the transmission function.