What causes automatic gear transmission failure besides the gearbox itself?

Not much to check,exccesive water to the tranny when hot may have hurt it.

Driving with the transmission submerged in water can cause the water to be sucked into the transmission. Drain the fluid to see if it has water in it or look on the dipstick and if the fluid is milky of frothy it has water in it. Water inside a transmission will ruin it pretty quickly. Also some of the electric connectors may have moisture in them causing issues.

Transmission control module is located in the passenger side floor area. It is prone to damage if there is water intrusion.

2009 VW passat automatic, reverse gear not working and forward working fine. Plus it's not showing on speedometer D or R or N sign. Any body help me what's the problem.

My 2004 wv passat is only going in frist gear and reverse but won't go in any other gears Wat is happening I just head gasket set job done and now it's only going in frist gear and resvese

2004 wv passat is only going in frist gear and reverse and just had head job done it was not doing this before

I drive a 2002 vw Passat and just had to replace a few things for problems like these. The most applicable issue here was definitely the transmission control module, which is located in a compartment underneath the passenger seat. Water gets in from a hole under the battery chamber and shorts the TCM, causing the car to go into emergency transmission mode: you can get into P, N, R, and D, but you'll be stuck in 3rd gear while moveing forward. You can tell this happened in because every transmission indicator on your dash will light up. To fix this, just remove the TCM and drain all the water, then replace it with a new one. You'll also want to take out the battery and clean out the hole underneath where the water seeped in or you'll have to pay $50 for a new TCM every time it rains.