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Preparing a dealer key on vehicles with a Megamos 48 transponder (incl. finding the 7th byte)

On vehicles that require a pre-coded key, the "dealer key" has to be prepared with the 7 component security bytes before learning. If you only have 6 bytes, the 7th has to be found using one of the available methods.

Procedure

1. In the "Key learning" special function press "Prepare dealer key": preparation requires the 7 CS bytes.
2. To obtain the component security you can press "Autodetect component security" (in Wizard mode: select "Autodetect component security" and press "Next"): the bytes are read from the ECU and the software decides automatically whether you have the 7th byte or whether it has to be searched for; the login is shown in the status bar as well. Autodetect works essentially on EDC16 and MED9x engines with a CAN diagnostic connection.
3. Alternatively, read the bytes with the "Engine Control Unit" special function: reading the engine ECU EEPROM makes the software show the component security bytes (at least 6 bytes are always present in the ECU, sometimes the 7th as well).
4. Or, for CAN TP2.0 immobilisers, in most cases all 7 bytes can be read from the cluster/immobiliser: go to "Special function" > "Instrument CAN" > "Read/write immo data"; after the read the 7 CS bytes appear in the "Serial Key" field.
5. If the 7th byte is other than "00" you have all 7 bytes: choose "All 7 bytes of the component protection data (component security are known)", enter the 7 bytes and press "Program" to program the transponder with the Key programmer.
6. If the 7th byte is not available, choose "Find the 7th byte of the component security data" and enter the six bytes you already have.
7. Search from a working key: if you have a key that starts the car, put it in the programmer and press "Find 7th byte from working key"; after 70-80 seconds the 7th byte is found.
8. Automatic search: this requires the immobiliser and the programmer to be able to read/write the transponder at the same time, so switch the ignition ON and rest the programmer's coil over the key sitting in the ignition switch. Note: on some models (e.g. VW Passat B6) automatic detection is not possible and the manual procedure has to be used.
9. Manual search: put the key in the programmer, then turn the ignition ON with it, then back in the programmer and so on until the byte is found; the software prompts you each time to put the transponder in the programmer and then in the ignition position. On most models the key stays in the ignition switch and only the transponder is moved (into the programmer and then close to the switch so the immobiliser can read it).
10. Passat B6 exception: you have to put the key with the transponder in the programmer, then the key in the ignition switch ONLY AS FAR AS THE FIRST POSITION, then back in the programmer and back in the switch, until the byte is found.
11. Preliminary check on whether the 7th byte can be searched for: connect to 25-Immobilizer, go to "Measured Values", channel 2; insert the original key or a key with a Megamos 48 transponder (the second position of channel 2 must read "yes" or "1"); pull the key out of the ignition switch. If the second position goes to "No"/"0" you CANNOT search for the 7th byte; if it stays at "Yes"/"1" you can.
12. With the dealer key/transponder ready, carry on with normal key learning: enter the number of keys to be learned and the security access code.
13. Megamos 48 keyless-go keys are also supported (e.g. VW Scirocco, Jetta, Golf 6, Tiguan, Touran 2010+ and others).

Reference screenshots