Very strange PDC problem
 

I am having an intermittent issue in which the PDC activates when turning the key to the 'start' position. Here is how it goes: Turn the key to the acc/on position, everything is fine and PDC is off as normal. Then turn the key further to start the X5, and immediately PDC comes on... This is without taking the car out of 'park' and putting it in reverse, etc. As I said it only happens intermittently, but seems to happen most frequently now when the car is cold. Not sure if this is related, but I have also been having an intermittent issue in which occasionally the car will not start in the 'start' key position until the 2nd try. Could a potentially failing ignition switch cause strange PDC behavior like this?

Thanks-

PDC module is located in the trunk, next to the battery. Is that area of the car dry? could there be any moisture? how old is your battery? has it drained recently?

PDC (A82) is getting power from Terminal 15 (ignition hot) and is activated via the telegram on the iBus, and also via the button on the central switch (A169) - theoretically, if everything is functioning normally, applying and removing power rapidly should not activate the PDC... failing battery on the other hand, is a known source of wild electronic behaviour in the system - the system generates random telegrams on the iBus which may result in flashing lights, windows going up and down, etc, etc, etc... the car acts as if possessed...

Check for loose wires, for dampness in the trunk area, then move onto more complex items...

Thanks for the reply. Trunk is very clean and dry. Battery is 2-3 years old, I believe. Car never hesitates to start once the starter engages. Interesting, though about the battery. Something else that just started happening is that my battery light flickers for about 3-4 seconds after starting the car, but only in the morning. I've searched up here and many folks have suggested in similar threads this indicates an alternator is starting to fail. Do you think this is also related to the PDC weirdness? I guess it's time to get the battery and alternator tested. :)

the light in the cluster for the battery is staying dark when the diode bridge on the voltage regulator from the alternator is working fine. when one of the diodes is going south, due to whatever factors (age, heat, too much juice...) the balance of the bridge is disturbed, and the light illuminates.

I do not know if the bridge or the regulator are repairable/replaceable individually, but that is a sign of the alternator... also, the electrical gremlins will manifest when the voltage is too high - it is just more common to see voltage too low, as in failing batteries, than to see voltage too high...

Thank you again for the very helpful insight. Would a voltage check at the terminals in the engine compartment while the vehicle is off and while running be a good test for verifying correct alternator charge current, or do I need a more sophisticated piece of testing equipment?

run a search on this forum, there were very recent (last few days) posts on how to get past the surface charge and get the reading while car is operating... do a search for surface charge, those posts will pop up... you will need to do the OBD test, there are also instructions on how to get to test #9 that read system voltage as you drive - you don't need equipment, it is already built-in