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Discussion Starter #21
Not likely for me to do that any time soon Blownvette. If you have laid out your entire harness, are you able to redraft the circuit diagram that the harness represents where any different to SS=+298?
 

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It looks clear to me from SS+298 and the circuit diagrams in it that the rear battery is dedicated for starting purposes (but it depends on some prior tests by the car). If voltage is <11.5V - then the starter battery is deemed discharged and then the Onboard Power supply battery becomes the battery providing power to start (as well as everything else - glow pugs, radio, whatever is on).

The three images below show the 3 possible scenarios when an engine start is required.

View attachment 235432

View attachment 235433
View attachment 235434

Pete
That diagram only shows a constant, direct connection to the under-seat battery. the only time it is disconnected from the starter motor is after a collision where the isolation relay has been triggered.
Yes all diagrams show the rear battery also connected, but it is also the only one with potential for disconnection.
 

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So what I posted was correct, thank you... Over the past 15 years of V10tdi ownership and 5 Touaregs I have been through more quirks than I can recall.
I had a under seat battery that was discharging its self and to start the car i had to turn the key to the left and bring in the rear battery. after replacing the front under seat battery no more problems in the past 12 months
 

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SSP298 states the parallel relay is disconnected until entry and start authorization module powers the relay.
Perhaps the left key turn bypasses the authorization module to activate the parallel relay itself, but would only occur if there was enough power in the on-board battery to do it.
Fairly certain left key turn doesn't work if on-board battery is disconnected. (or fully discharged)
 
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