B. Vehicles With DAS
As of Model Year 1996, all models (excluding models mentioned, under subject A) are equipped with the Drive Authorization System (DAS). This system increases the theft resistance of the vehicle by disabling fuel injection if the vehicle is not properly unlocked, either via the IRCL system or with the key. This system uses the CAN Bus to transfer data from the IRCL control module to the engine control module during each starting attempt.Operational Description - DAS
This operational description applies to all vehicles with DAS. Vehicles described under subject A are not equipped with DAS, therefore this description does not apply.
The IRCL module is programmed by the manufacturer with a specific Identification (ID) number, which is cross-referenced by Mercedes-Benz to a specific Vehicle Identification Number (VIN). This ID number remains with a specific VIN for the life of the vehicle, and must not be changed (for example, by installing the module from another vehicle to expedite a repair). From this ID number, a certain code number is calculated.
When first installed, the engine control module has no information about the IRCL system's code. At the time of installation, the engine control module must be version coded, which includes a 9-digit engine type code (obtained from the old module, or the parts microfiche/EPC), and the vehicle's VIN (without the WDB). Once the version coding (performed with the HHT) is completed, the identification process must be performed. This procedure is performed by following the screen prompts on the HHT. In this identification procedure, the engine control module learns the IRCL code number. If "Identification" is not performed, the vehicle will not start.
After "Identification", the engine control module begins counting the number of engine starts (where the engine speed exceeds approx. 500 RPM - not starting attempts). When this count reaches a specified number (40), the engine control module stores the IRCL code permanently, and then is permanently "married" to that specific vehicle. If desired, the "marriage" can be forced to occur immediately, using the HHT. Until the marriage process is complete, the module can be version coded for another vehicle as often as desired. At each recoding, the counter begins again from zero.
Once the engine control module has completed the identification process, the DAS system is operational. The process followed by DAS for authorizing a starting attempt proceeds as follows:
When circuit 15 (ignition) is switched on, the engine control module generates a random number. This number is sent to the IRCL module via the CAN Bus. The engine control module uses this random number along with the code number to calculate an authorization number. At the same time, the IRCL module performs the same calculation with the random number and the code number. The IRCL sends the resulting authorization number back to the engine control module, which compares it with the number it calculated. If the authorization numbers match (meaning the code numbers also match), the starting attempt is "authorized", and fuel injection is permitted, allowing the engine to start. At the same time, if the numbers match, the engine control module sends a message via CAN Bus to the IRCL, confirming that the start is authorized.
If the numbers did not match, fuel injection is disabled (the engine will not start), and no message is sent to IRCL. When the IRCL sees circuit 50 (starter solenoid signal), it checks if a message was received authorizing the start, and if no message was received, the red and green lamps in the rearview mirror are flashed alternately. Of course, if the start is authorized, then the IRCL takes no action.
Troubleshooting Flowchart - Engine Does Not Start
Use this troubleshooting flowchart to determine which vehicle system (engine control module [ECM] or IRCL) must be diagnosed to resolve complaints of "Engine Cranks but Does Not Start". Refer tot he Diagnostic Manual for complete diagnostic tests.
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EBQ:
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Troubleshooting Chart - IRCL
Use this troubleshooting table to determine with specific portion of the IRCL system may have a fault.