1. Driving Conditions & Baseline State I was operating my new 2026 Porsche Cayenne (current mileage approx. 717 miles) at highway speeds inside a tunnel near LAX. The vehicle was functioning normally under normal driving conditions until the incident occurred suddenly and without any prior warning signs. 2. Onset of Failure & Dashboard Alerts - While maintaining speed, the vehicle suffered an immediate, simultaneous electronic and mechanical malfunction. The dashboard abruptly displayed an Adaptive Cruise Control (ACC) error/failure warning, along with auto start/stop failure. Immediately following this alert, the vehicle experienced a severe, sudden loss of mechanical power and propulsion. 3. Vehicle Behavior & Safety Hazard Pressing the accelerator pedal failed to yield normal engine response or acceleration. The drop in power felt as though the vehicle entered an unprompted "limp mode" or suffered a critical powertrain/software communication failure, severely limiting my ability to maintain highway speeds. Because this occurred inside a highway tunnel, the sudden deceleration presented an immediate and extreme safety hazard, nearly causing a rear-end collision with the traffic behind me. I was forced to navigate the underpowered vehicle out of the active lanes of traffic under highly dangerous conditions. After pulling over to a safe area and cycling the ignition (turning the vehicle off and back on), the mechanical power partially/fully returned, suggesting a transient or software-driven electronic control unit (ECU) fault. The historical error codes should be stored in the vehicle's modules. 4. Post-Incident State The vehicle was presented to McKenna Porsche (Norwalk, CA) the following day for diagnosis of the power loss and ACC failure. Safety Implications & Requested Action This component failure constitutes a critical safety defect. A total or partial loss of propulsion at highway speeds poses an unreasonable risk of severe injury or crash.

On 3 separate occasions while making a left hand turn against traffic, the car has initiated emergency braking and shown the ‘collision warning’ alert on the dashboard. Each time there were no cars approaching and the car halted to a complete stop. The first two instances I had my 10 year old in the car. Tonight I was alone. It is terrifying and I know this is not a rare occurrence with Porsches. An online forum has tons of other Porsche owners saying the same thing and we are being encouraged to file a report with NHTSA.

The emergency braking system light and the adaptive control cruise control is not working in the warning. Lights are on from Dave that I’ve got it from day one January 2026.