BRZ Auto Trans Issues: Harsh Shifts & Limp Mode

I had a very similar issue with my 2018 Toyota GT86 automatic. With low experience working on cars myself, I relied heavily on my regular workshop to diagnose and fix the problem. The symptoms matched yours exactly, rough shifting, occasional limp mode activation, and sporadic powertrain warning lights. The diagnostic trouble codes initially pointed to transmission issues, but it turned out the root cause was different. The workshop discovered that faulty ABS wheel speed sensors were sending incorrect signals, causing the transmission control module to receive conflicting information. This led to the erratic shifting patterns and occasional fault codes. Since the traction control and ABS systems are interconnected, the transmission was getting confused by the bad data. The fix was actually covered under warranty in my case, as it was a known issue. The technician cleaned the sensors and reset the fault codes, which completely resolved the symptoms. No parts needed replacement. To better assist with your situation, could you share: Have you scanned for specific fault codes? Does the issue occur more frequently at certain speeds or temperatures? Are there any unusual noises from the wheel areas during acceleration or braking? Has the ABS light ever illuminated? This information would help determine if your BRZ is experiencing the same root cause.

Thanks for sharing your experience. Just had my latest service at 39110KM and they did a full transmission health check. The fault codes were read but cleared after a few days. Have noticed the symptoms are worse when the transmission fluid is cold, especially during the first 10 minutes of driving. Had the transmission shop perform a diagnostic and they mentioned the torque converter might need replacement, but wanted a second opinion since its a costly repair. No unusual noises from the wheels and the traction control system seems to function normally. The gear selector movement is smooth but the actual gear engagement is what feels off.

Thanks for the additional details about your BRZ. The cold fluid behavior is particularly telling, my GT86 exhibited similar symptoms when cold before the repair. However, based on your description, I suspect your issue might be different from my wheel sensor situation. The fact that your gear selector feels normal but engagement is rough points more toward an internal transmission issue. When my transmission control module received bad sensor data, the gear selector would occasionally feel notchy or resistant. Since you mentioned the transmission health check, did they perform a pressure test? Low pressure in cold conditions often indicates worn components in the valve body or torque converter. While these repairs are expensive (typically 2000€-3000€), ignoring them could lead to complete transmission failure. Before committing to the torque converter replacement, request these specific checks: Transmission pressure test (both cold and operating temperature), Full transmission control module diagnostic scan, Solenoid resistance testing When my car went into limp mode, it was intermittent. Your symptoms sound more consistent and temperature-dependent, which aligns more with mechanical wear than sensor issues. Getting these additional tests will help confirm whether the shop's torque converter diagnosis is accurate.

Thanks everyone for the insights. After getting the additional diagnostic tests done as suggested, the transmission pressure test revealed significantly low pressure when cold, confirming the initial suspicion about the torque converter. The transmission control module showed multiple fault codes related to irregular pressure readings, especially during cold starts. I decided to proceed with the torque converter replacement since the symptoms matched the diagnosis and I want to prevent more extensive transmission damage. The repair is scheduled for next week and will cost 2800€ including labor. While expensive, it seems worth it to fix the issue properly rather than risk more serious problems. Will update once the repair is complete, but based on all the feedback here, I feel more confident about the diagnosis and repair plan. Hopefully this helps others who might encounter similar transmission issues with their BRZ.