VW Lupo Auto Trans Failure: Gearbox Slip & Grinding Issues

As someone with some hands-on experience, I dealt with very similar symptoms on my 2004 VW Polo automatic. The transmission issues you describe sound familiar, especially the grinding during shifts and emergency mode activation. After using a pressure gauge to check the transmission, my workshop found that a cable connection to the transmission control unit was damaged, causing incorrect readings and making the system think there were serious issues. The cooling system and radiator were actually fine, it was just sending wrong signals. The fix involved replacing the wiring harness connector and recalibrating the transmission control module. Total cost was 95€ for parts and labor. The transmission has worked perfectly since then, no more warning lights or emergency mode. Before jumping to conclusions about major transmission work, we should check some details about your car: Have you noticed any fluid leaks under the car? Did you do any recent transmission maintenance? What color is your transmission fluid? Are there any other warning lights besides check engine and transmission? This could help narrow down if you have the same underlying issue or something different. Proper leak detection and pressure testing would be good first steps before assuming worst-case scenarios.

Thanks for the replies so far. Just had my latest service 2 months ago, and my odometer shows 117554km. The transmission fluid is reddish-brown and clean, no leaks visible underneath. The radiator coolant level seems normal, but I noticed the cooling fan runs more frequently than before. My mechanic did a pressure sensor test but couldn't pinpoint the exact issue. The transmission problems started right after a long highway drive during hot weather. I checked the service records and found the transmission fluid was never changed since I bought the car 3 years ago. Could this be related to the current problems?

Thanks for providing those details about your Lupo. The cooling fan behavior combined with transmission issues after highway driving raises some concerns about the cooling system performance. While your radiator coolant level looks good, the transmission fluid being unchanged for 3+ years could definitely contribute to these symptoms. Degraded transmission fluid loses its cooling and lubricating properties, especially under high-stress conditions like extended highway driving in hot weather. On my Lupo, I faced nearly identical issues at around 120000km. The root cause turned out to be a partial coolant leak in the transmission cooler section of the radiator, which allowed cross-contamination between the cooling and transmission systems. The pressure gauge readings were inconsistent because of this. The fix required: Radiator repair and replacement of affected cooling system components, Complete transmission fluid flush and replacement, New transmission filter, System pressure testing to confirm proper operation Total repair cost was around 650€, but it resolved all the symptoms completely. The transmission shifted smoothly again and no more warning lights appeared. Given your symptoms and maintenance history, I strongly recommend having the cooling system and transmission fluid checked thoroughly. Early intervention can prevent more extensive damage to the transmission.

Thank you for the detailed responses and suggestions. Following up after getting a second opinion from another workshop. They performed a complete diagnostic with leak detection tools and found small cracks in the transmission oil cooler lines. This explains the increased cooling fan activity and transmission problems. The workshop confirmed cross-contamination between coolant and transmission fluid occurred, similar to what you experienced. They proposed replacing the oil cooler, flushing both systems, and installing new fluids and filters. The quote is 580€ for all parts and labor. This makes sense given the symptoms started after that long highway drive in hot weather. The old transmission fluid probably contributed to the issue by not providing adequate cooling under stress. I will proceed with the repairs next week and update once completed. For now, they advised minimal driving and keeping the engine temperature in check by avoiding heavy loads. The grinding noises during shifts have actually gotten worse, so better to fix this sooner rather than later.