Horse drawn vehicles had wooden wheels with steel tyres. Their brakes usually consisted of blocks of wood, mounted on pivoted brackets which could be forced against the steel tyres. Early motor cars with solid rubber tyres retained this type of braking. As speeds increased and vehicles became heavier this braking system used to destroy the tires due to heat and abrasion.
Antilock brake systems (ABS) have been introduced on many passenger car and light truck make/models in recent years. Brake experts anticipated that the introduction of ABS on passenger vehicles would reduce the number and severity of accidents. A number of statistical analyses of accident databases have been performed during the last three years. These analyses suggest that the introduction of ABS does not seem to have reduced the number of automobile accidents where they were expected to be effective. Kahane stated that involvements in multi-vehicle crashes on wet roads were significantly reduced by 24 percent, and nonfatal crashes by 14 percent (with ABS). However, these reductions were offset by a statistically significant increase in the frequency of single-vehicle, run-off-road crashes (rollovers or impacts with fixed objects), as compared to cars without ABS. Fatal run-off-road crashes were up by 28 percent and nonfatal crashes by 19 percent. It is unknown to what extent, if any, this increase is due to ABS or other causes. It is also unknown to what extent, if any, this increase is due to drivers incorrect usage of ABS or incorrect responses by drivers to their ABS.
The ABS control module is a microprocessor that is used to manage the operation of the ABS system. The ABS control module monitors and processes information from various sensors, modulates pressure to the brake system and carries out self-diagnostic tasks. Some of the inputs to the ABS module are the wheel speed sensors, brake switch, brake warning light, parking brake switch, pressure modulation devices and ignition and power feeds. The output controls consist of brake pressure modulation components and the anti-lock brake lamp. Most ABS control modules have the ability to run self diagnostic tasks and store trouble codes for failed diagnostics. The ABS control module can display this information to a scan tool or through flash codes, via the dash mounted anti-lock brake light, making troubleshooting and repair more accessible. Some ABS control modules store sensor information when a failed diagnostic is recorded. This can assist automotive technicians in diagnosing ABS trouble codes by displaying a record of sensor information at the time of the failed diagnostic.