Some Mustang cars made between 2020 and 2023 have a problem with their brake fluid level sensor. This sensor doesn’t activate a warning light when the brake fluid is low. As such, these vehicles fail to comply with the requirements of Federal Motor Vehicle Safety Standards for light vehicle brake systems.
Ford became aware of the problem in August 2023 when an issue pertaining to 2020-2023 model year Mustang brake fluid level warning systems was brought into Ford’s Critical Concern Review Group (CCRG) for review. They discovered that the problem lies with the Body Control Module (BCM), a part that manages the brake fluid sensor. This BCM should turn on the brake warning light if there’s a problem. In Mustangs made from 2018 to 2023, the brake fluid sensor is directly connected to the BCM. However, in the 2020 Mustang, they switched to a different BCM design, called “Gen1m,” which incorrectly looks for a message from the brake fluid sensor over a network (CAN) instead of the direct connection.
After investigating, Ford confirmed that this problem only affects Mustangs from 2020 to 2023. They also verified that the 2024 Mustang doesn’t have this issue because the brake system and BCM are set up correctly. The Brake Development team tested Mustangs from 2019 to 2024 and found that the 2020 to 2023 models fail to meet the requirements for warning about low brake fluid. However, these vehicles meet all other brake system warning lamp requirements.
Ford initially didn’t run certification tests on the 2020 to 2023 Mustangs because they thought the brake system was the same as in the 2018 model. They didn’t know that the BCM was incorrectly configured to use a network message.
As of September 12, 2023, Ford received 123 warranty claims related to a brake fluid loss on these vehicles, but there were no reports of the brake fluid level sensor not working.
To fix the problem, Ford dealers will update the software in the body control module. They plan to send out initial letters in December 2023 to notify owners about the safety issue and will send second letters when the solution is available. This recall is identified by Ford as number 23C35, and the NHTSA campaign number is 23V-727.