ABS (Anti-Lock Braking System)

What It Means

An Anti-Lock Braking System (ABS) uses wheel-speed sensors, a hydraulic control unit (HCU), and an electronic control module (ECM) to detect when a wheel is about to lock up during braking and rapidly modulate hydraulic pressure to that individual wheel, preventing the skid while maintaining stopping power. Modern 4-channel ABS cycles pressure at each wheel up to 15 times per second, which is why drivers feel a characteristic pedal pulsation during hard ABS-activated stops. ABS has been mandatory on all new passenger vehicles sold in the U.S. since model year 2013 under FMVSS 126, which actually requires Electronic Stability Control, but ESC is built on top of ABS, making ABS a prerequisite. ABS is also foundational for many more advanced systems: Electronic Stability Control (ESC, FMVSS 126), Traction Control (TCS), Automatic Emergency Braking (AEB), and Adaptive Cruise Control all rely on ABS wheel-speed sensor data and the ability of the HCU to apply individual-wheel braking. ABS-related recalls typically involve: wheel-speed sensor failures (bearing corrosion contaminating sensor signals), HCU hydraulic pump motor failures, brake fluid leakage from the HCU causing loss of brake pressure, and, most seriously, brake fluid leaks onto ABS control module circuit boards, which has been the root cause of multiple Ford recalls dating back to 1999, ultimately covering more than 15 million vehicles and involving confirmed engine-compartment fires due to electrical arcing in the contaminated module. The Toyota unintended acceleration investigation of 2009-2010 also included an ABS software component, where certain hybrid models had a programmed one-second brake-pedal delay at low speeds in slippery conditions, leading to a 2010 recall of 133,000 Prius hybrids.

ABS (Anti-Lock Braking System) is one of the NHTSA or vehicle-safety concepts that recurs across RecallIndex. The definition above is the technical answer; below is how the concept connects to the NHTSA data that drives every vehicle page on the site.

In the RecallIndex Safety Score, this concept feeds one of the four factor weights — recall severity (40 percent), complaint frequency (30 percent), crash and fire reports (20 percent), or trend direction (10 percent). The methodology page on the site walks through every input in detail.

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