VW Jetta TDI Cabin Heat Issues: Failed Sensors Guide

I dealt with a similar heating issue on my 2004 VW Golf TDI. As someone with moderate experience working on VW diesel engines, I initially thought it was a temperature sensor malfunction. After having the fault codes read, it turned out the HVAC sensor wiring connection was loose, causing erratic temperature readings. The daylight sensor was working fine, but the main temperature sensor was getting inconsistent signals due to a damaged wire harness connector. The fix involved replacing the damaged connector and properly securing the wiring. Total cost was 95€ including diagnostic work. Since then, the heating system has worked perfectly with consistent temperature control. Before suggesting specific fixes for your Jetta, it would help to know: Which error code is showing up? Does the issue occur right after starting or only after driving for a while? Have you noticed any changes in engine temperature readings? Are there any other electrical issues present? Fault detection in these models can be tricky since multiple sensors work together in the HVAC system. Getting the exact error code would help narrow down whether its truly a sensor issue or possibly something else in the heating circuit.

Thanks for sharing your experience. My car shows error code P0116. The heating problems start immediately after a cold start and persist throughout the drive. Engine temperature readings appear normal on the dash. No other electrical issues noticed. Just had my latest service 2 weeks ago where they changed oil and filters, but the heating problem started after that. The sunlight sensor seems to be responding when tested, but the HVAC sensor might need recalibration since the temperature control acts erratic regardless of settings. Would dealing with the wiring harness connector be something I could check myself, or should this be left to a professional given the sensor calibration requirements on these VW models?

Thanks for those additional details, especially about the P0116 code and timing after the recent service. Since I dealt with similar symptoms on my Golf TDI, I can share some relevant insights. The P0116 code typically points to the engine coolant temperature sensor circuit rather than the HVAC or sunlight sensor systems. Given that your issues started after the service, there is a good chance the temperature sensor connector was accidentally disturbed during the maintenance work. On my Golf, accessing the engine coolant temperature sensor was fairly straightforward, its located on the cylinder head near the thermostat housing. The wiring connection can be checked without special tools, though sensor calibration afterward requires diagnostic equipment. A few specific suggestions based on my experience: Check if the temperature sensor connector is fully seated and locked, Look for any pinched or frayed wires near the sensor, Verify coolant levels are correct post-service, Have the temperature sensor resistance tested While you can inspect the wiring yourself, I would recommend having a shop handle the actual repair since proper sensor calibration is crucial for these VW HVAC systems to function correctly. The repair cost should be similar to what I paid, around 100€ depending on whether the sensor itself needs replacement.

Thanks for the detailed suggestions. That P0116 code being related to the coolant temperature sensor makes a lot of sense, especially since the problems started right after the service work. I will check the sensor connector and wiring myself first, but leave the actual repairs to the professionals given the calibration requirements. I made an appointment at my local shop for next week. They quoted roughly 120€ for diagnostic work and sensor calibration if needed. Will let them verify the coolant levels and test the temperature sensor resistance as you suggested. Good to know the repair costs should be reasonable if it turns out to be just a disturbed connection. Much better than having to replace the entire HVAC system which I initially feared. Really appreciate everyone sharing their experiences with similar automotive sensor issues. Will update once I know what the actual problem turned out to be.