2024 Toyota Highlander Power Train

Detailed Description of the Incident: I am reporting a recurring powertrain safety issue regarding the 8-speed automatic transmission (UA80-series) in my vehicle. [Symptoms] During cold-start conditions (outside temperatures below 30°F), the vehicle consistently experiences a violent jerk/shock and an audible clicking noise during the first 2nd-to-3rd gear transition. This physical impact is severe enough to be felt directly by the driver through the accelerator pedal. The issue is highly predictable, occurring once after every "Cold Soak" period (6+ hours of sitting). [Dealership Failure] I presented the vehicle to an authorized Toyota dealership for diagnosis. Although the conditions for the issue were met, the technician stated they "could not feel or verify" the shock that I, as the primary driver, clearly experience. By failing to acknowledge a physical powertrain shock, the dealership is dismissing a potential mechanical failure as "normal operation" simply because no Diagnostic Trouble Codes (DTCs) are triggered. [Safety Risk] The failure to verify this symptom does not eliminate the safety risk. This unexpected shift shock causes a momentary hesitation in power delivery. If this occurs while merging into traffic or navigating an intersection immediately after a cold start, it creates an unpredictable vehicle response, significantly increasing the risk of a rear-end collision. [Request] I request NHTSA to investigate this specific 2-3 shift shock in 2023-2024 Toyota Highlanders. Toyota’s reliance on electronic codes to diagnose physical transmission defects is leaving drivers at risk of sudden powertrain failure or accidents in cold climates.

While slowing down, the vehicle will suddenly lunge forward, as if It hit a patch of ice and then slow again. This started happening around 30,000 miles. The dealer said this is because of a transition between hydraulic braking and regenerative braking and is "NORMAL". This did not start until 30k miles. I have owned 4 hybrid vehicles and only this one does this. Upon reading and studying online, there was a bulletin for an earlier generation of this type of problem. Clearly, it is an issue as I am not the only one with this problem.