porschetestdriver

Hello all
My first post. I have otherwise figured everything else prior with all your help and research but this has me stumped.
1. The car power is good but will not crank. No clicking or any other sounds or signs that it is the battery or stater. l all displays are normal . I checked the alarm thinking it was some kind of immobilizer VAG does not show any errors. I have have tried different keys
2. The car also does not display the tiptronic anymore just the PRND432
I dont know if the transmission TCM is the problem or the switch that tells the tranny what gear it in there for it wont start or if it a relay somewhere.
any help would greatly be appreciated
Thanks

silverd2

Well, the F125 switch on the trans is part of the maze. There could be many places to look for a problem:

According to Bentley wiring diagrams:

Starter switch goes straight through the starter interlock relay, which only works if it's closed. That relay actually gets it's signal to close straight from the central locking module, which seems to get it's OK from the ECM (engine control module). The ECM gets a neutral or park confirmation from the F125 switch on the trans.
Diagrams do not show any direct connection from the trans (or TCM) to the starter interlock relay...so it apparent has to take the route above.

You've probably already tried to start in N & P.
I'd want to go straight to the starter solenoid next...put 12v strait to the solenoid wire...starter should run.
Then I'd go to the ignition switch...make sure 12v is sent out of wire to interlock relay.
Then check to see relay is getting energized by the central locking module...doesn't have to be an alarm problem, it's just in the route, getting it's OK from the ECM.
If no progress, then on to the ECM box...check for water intrusion, corrosion on contacts, etc.
Then on to the F125 switch plug on the trans...no oil, good contact, etc.

Of course you trace this all backwards too...but, looks like something in that whole circuit(?)

The interlock relay is under the passenger's footboard in central electrics (right side w/LHD)...#4 position (from left) on 6 position relay board.

Haven't had the problem myself, but hope this gets you started tracing it.

tozoM8

If it does not start in N then it is the ignition switch.

silverd2

Argh!

You and your one line (and almost always correct) answers

Proph3t

Hi porschetestdriver,

Any outcome or solution for this one? I have a very similar, if not identical issue? (that silverd2 and tozoM8 are helping me with also)

Thanks.

porschetestdriver

It was the wiring going into the horn relay the ground {brown wire} and the switched +12 {yellow Black Stripe wire} were interrupted.

Proph3t

ok, so where were these located? How does a horn relay ground effect start up?

giotown

i bump this for my black beast as well