Goughary

I had a car in the garage today that I was bleeding- C4 - the pdt999 couldn't connect to the pdas. But it couldn't connect to motronic either - when I hit connect to pdas, you heard the click that it was connecting, and then another click and the screen said "cannot connect". No idea why.

Don't know if it's related but the hvac controller doesn't turn on the fans or the ac compressor. It's dead.

All fuses were checked and the relays were swapped with the working ones from my car to test. No difference.

Thoughts? We bled the diff locks manually in the end with the center console control switch. But why the pdt won't connect to the pdas or the motronic ecu is baffling

Nineone1fun

The only time i do get this problem is when the ignition key is not engaged in the first position.
It may not de in your case but would mean a power supply issue .
DME relay ?

dlpalumbo

From the user manual, alarm module version 100 and Tiptronic ECUs can have difficulty connecting. Then goes one to say other modules may have trouble as well.

Not sure how you'd know if you had 'alarm module version 100'.

My pdt999 complains of failure to do fuel adaptation, then it works just fine.

I have version 1.8 of docs. May be more up-to-date on their site.

I'd WAG voltage or ground problems. Did you try software tool? It may have different sensitivities to whatever issue you're having.

Dan

cajonfan

My guess is that the diagnostic communications lines (K and L) are being loaded by one or more of the interconnected units, so that none of the controllers can communicate. Given your observation of a "dead" CCU, that might be the culprit. You could pop out the CCU and see if everything else becomes chatty again.

Goughary

I'll give that a shot when he comes back. It's a head scratcher for sure.