ELEKTOR FORUMS

Although the OBD connector in the car has a constant +12 V supply on one of its pins, the ECU in general will not start supplying data until the ignition is switched on. Hence the following order of connecting and powering up the equipment is recommended for all cars.

1. Have the software up and running on a PC or laptop
2. Power up the OBD Analyser
3. Switch on the car ignition
4. Insert the OBD cable plug into the car's OBD connector.

This should enable the OBD Analyser firmware to establish the protocol used.

Step 4. requires certainty that no (static) voltage difference exists between the OBD Analyser ground and the car chassis.