Touareg Coolant Leak + Overheating Points to Head Gasket

My VW Tiguan 2016 had very similar symptoms. The control module was actually fine, but the issue turned out to be more serious. The water pump housing had developed hairline cracks, causing coolant leaks and system pressure problems. Car diagnostics revealed multiple issues: the electronic thermostat was failing intermittently, which led to incorrect temperature readings and communication faults between control units. This explained the engine warning light. The main problem was that the failing thermostat caused pressure buildup, which worsened the crack in the water pump housing. It created a cycle where the cooling system would overpressurize, leading to more leaks. The repair required: Complete water pump assembly replacement, New thermostat installation, Cooling system pressure test, Control module reset This was not a quick fix job. The entire cooling system needed inspection and several components replacement. The wiring issue with the thermostat also required attention to prevent future communication faults. Consider requesting a pressure test of the entire cooling system before replacing individual components. Often, these symptoms indicate multiple related issues rather than a single faulty part.

Thanks for your detailed response about the water pump and thermostat issues. This seems very similar to my situation. The data link problems and system pressure buildup you mentioned definitely match what I am seeing. Did any other connectivity issues come up after the repair was completed? Also wondering what the final cost was for all the work, including the control unit reset and system inspection. My local shop gave me a rough estimate but I would like to compare. Would be great to know if everything has been running smoothly since the fix. I want to make sure I address all potential issues at once rather than having to go back multiple times.

Since having the data link connection repaired last month, my Tiguan has been running perfectly with no overheating or diagnostic trouble codes. The control unit communication error disappeared completely after fixing a loose cable connection at the thermostat sensor. The final repair costs were actually lower than originally quoted since the software glitch and wiring issue turned out to be simpler than expected, just 95€ for reconnecting the faulty plug. This was much better than potentially replacing the entire control unit as initially feared. The cooling system pressure has remained stable and I have not seen any error messages or warning lights since. The mechanic ran a full diagnostic scan afterward to confirm all communication between control units was restored. Getting the electrical connection fixed first helped identify that the thermostat and water pump were actually working correctly. Would definitely recommend having them check the wiring and connections before replacing major components. A proper diagnostic scan can save significant money by pinpointing the actual source of communication faults.

I took your advice and had my Touareg checked out. The diagnostic trouble codes pointed to exactly what you described, a combination of issues rather than a single problem. Just like your case, they found hairline cracks in the water pump housing causing pressure problems. The repair took two days but was worth it. They replaced the water pump assembly, installed a new thermostat, and fixed a loose wiring connection that was causing communication faults between modules. The total came to 780€ including parts and labor. After a week of driving, the engine runs at normal temperature with no warning lights. No more coolant puddles under the car, and the data link is working properly with no software glitches. Really glad I had them do a complete diagnostic instead of just replacing parts one at a time. The mechanic also pressure tested the entire system to confirm everything was sealed properly. Turns out getting it all fixed at once saved money compared to multiple separate repairs.