CTS Window Defrost Failure: Troubleshooting & Fixes

I had a similar issue with my 2001 Cadillac Catera. As someone with some experience working on these models, I can share what worked in my case. The main problem turned out to be a heavily discharged battery that was causing electrical system issues, including failure of both the front and rear window defroster systems. The heating coil connections were fine, but the system wasnt getting proper power. The repair involved: Complete battery replacement, Testing of the window demister circuits, Checking all fuses and relays related to the auto defrost system, Clearing the stored error codes Total cost was 290€ at my regular workshop, including parts and labor. The fix resolved both the front and rear window defrost issues completely. Before suggesting more specific solutions, could you share: Current battery age and condition, Whether the defroster problems started gradually or suddenly, If you notice any other electrical issues, The specific error codes stored This would help identify if your issue matches what I experienced or if its something different with your defroster repair needs.

Thanks for the battery replacement suggestion. Unfortunately, that wasnt the issue in my case. After further diagnosis, my rear defroster and front window heater problems stem from a faulty control module. During my last service at 150284 KM, the mechanic found corroded wiring connections at the rear window heating elements. The module itself shows signs of water damage, which explains the inconsistent heating performance and error codes. The repair estimate is around 450€ for parts and labor to replace both the control module and repair the damaged wiring harness. Has anyone attempted fixing just the wiring without replacing the entire module? Its quite expensive and Im wondering if theres a more cost-effective solution for the defroster repair.

Thanks for sharing those additional details about your defroster problems. On my Catera, I actually faced a similar situation with the control module after ruling out the battery issue. While the wiring repair alone might seem tempting, I learned the hard way that its usually not a lasting fix when the control module shows water damage. I initially tried just fixing the corroded connections at the rear window heating elements, spending about 120€, but the thermal window system failed again within 2 months. The control module is critical for both the front and rear defroster operation. When I finally did the complete repair with module replacement and new wiring, it cost me 480€, but its been working flawlessly for 2 years now. The rear window heating performance returned to normal, and the error codes cleared permanently. One cost-saving tip: while replacing the module, ensure the drainage channels around the rear window are completely clear to prevent future water damage. This step is often overlooked but crucial for preventing the same heating issue from recurring.

Thanks for the thorough feedback on the control module issue. After considering both options, I decided to go ahead with the complete repair including both the module and wiring. You made a good point about the temporary nature of just fixing the wiring, I dont want to risk having the car defrost system fail again in a few months. The shop is scheduling the work next week. They confirmed the 450€ estimate and mentioned theyll clean out those drainage channels you mentioned while doing the rear defroster repair. The mechanic also found a small crack near one of the heating coil connections that could have been letting moisture reach the module, so theyll seal that too. Really hoping this fixes both the front and rear window heating problems completely. Its been frustrating dealing with foggy windows, especially since the auto defrost function stopped working. Will update once the repair is done in case anyone else runs into similar window demister issues with these models.