Preliminary Evaluation PE24-001: Loss of braking performance

On January 11, 2024, the Office of Defects Investigation (ODI) opened PE24001 to investigate instances of loss of braking performance in model year (MY) 2023 Fisker Ocean vehicles manufactured by Fisker Group Inc. The complaints allege an intermittent partial loss of regenerative braking over low traction surfaces, without alerting the driver. ODI is aware of six minor crashes and one injury due to this failure. The subject vehicles utilize a brake blending feature to achieve deceleration. Upon application of the brake pedal, both the service brake system (friction braking) and regenerative braking system (electric motor negative torque) are applied. Regenerative braking on low friction road surfaces may result in wheel slippage due to the high motor negative torque. The vehicle responds by reducing and/or eliminating regenerative braking torque to reduce wheel slip on drive wheels to maintain vehicle stability and steerability. This reduction in regenerative braking may cause a sensation of loss of braking force (or even vehicle accelerating) that was reported by consumers. Additionally, the driver may experience an unusual/altered brake pedal feel during loss of regenerative braking events, requiring them to press the brake pedal harder to maintain the expected braking rate. Upon exiting the low friction road surface, the regenerative braking force is restored. The initial calibration of the regenerative braking system contained aggressive interventions with a slower recovery in the event of loss of regenerative braking. In November 2023, Fisker launched an Over-the-Air update (OS1.10 SW). This update included a recalibration to reduce regenerative braking torque less aggressively and allow torque recovery to occur more quickly. Based on consumer reports and the data that Fisker provided in response to ODI’s inquiry, OS 1.10 SW reduced, but did not eliminate, the sensation of loss of braking force and resulted in stopping distance performance improvements. Friction braking is always available when the driver presses the brake pedal, and its performance is unaffected by regenerative brake loss. Fisker’s braking system is designed to reach full deceleration even with an unavailable regenerative braking system. The partial loss of braking force during moderate braking events can be overcome by applying additional pressure to the brake pedal to slow or stop the vehicle. On August 20, 2024, Fisker filed recall 24V-623 for all 2023 MY Fisker Ocean vehicles produced for the U.S.A. The recall remedy includes OS 2.2 over-the-air update, which is expected to modify the brake module to enhance the vehicle brake system’s ability to adapt to various driving scenarios. With successful implementation of OS 2.2, a road disturbance will not trigger a reduction in regenerative braking torque. In view of the recall action being taken by Fisker, ODI is closing this Preliminary Evaluation. The agency reserves the right to take additional action if warranted by future circumstances. To review the reports cited in the Closing Resume ODI Report Identification Number document, go to NHTSA.gov.