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have a 2004 passat 2.8 v6 4motion tiptronic with a transmission related issue.

i think this may be an electronic issue not a mechanical one

140,000km (87000 miles)

***absolutley no water or moisture ingress around trans computer under rhs carpet

put a cheap code reader and car had no faults, reader is talking to car as it is able to pull live engine data off the motor (things like rpm fuel trims throttle percentage and so on)

problem is : when driving normally with car in "drive" (ie d on shifter) under light throttle transmission should be in a gear and holding it not changing, car is reving up or flaring suddenly and banging/clunking in the driveline and then settling back down to the rpm it was on before it flared the rpm up. this is happening in circumstances where the car should be in any given gear and holding the gear not trying to up or down shift (eg crusing along flat highway at 80-100kmh (40-60mph)at 1800-2000rpm). it feels like either 1. the car is trying to change gear suddenly and then changes its mind or 2. it is traveling with torque converter locked and decides to unlock completly and then suddenly decides to lock again allowing the revs to flash a couple of hundred rpm... the banging is a mechanical bang, it feels like the transmission has disconnected from the motor and then reconnected suddenly and the bang is all the slop between the front of the gearbox and the wheels being taken up suddenly

it does NOT do this at all in tiptronic mode ~ it only does this with transmission in automatic mode (ie d,4,3,2).... in tiptronic if you select any gear it just holds the gear and does not do this sudden disconnect ~ hence why i think its electical...

there is no flare at all between gear changes in drive... ie accelerating from standing start the gears all change as they should no little rpm flares/jumps as it moves up through the gears.

i have not checked the trans oil level, but this should be fine as the car has no oil leaks.

are there any problematic areas of the wiring loom that may get worn out through rubbing etc, plugs that may come loose or let moisture in, sensors that begin to fail etc on these cars that could create this kind of scenario?

thanks in advance for any help
 

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You may need a VCDS tupe reader to read the trans. A bad temp sensor in the harness can cause this, but few cheap readers can pull that info.
 
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