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.

PORSCHE CAYENNE 2026 POWER TRAIN

On 3 separate occasions while making a left hand turn against traffic, the car has initiated emergency braking and shown the âcollision warningâ 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.

PORSCHE CAYENNE 2026 FORWARD COLLISION AVOIDANCE: WARNINGS

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

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