Which sensor is primarily used to detect wheel lock or slip and monitor traction?

• A. Wheel speed sensors
• B. Temperature sensors
• C. Pressure sensors
• D. GPS sensors

Answer: (A)

Detecting wheel lock or slip and monitoring traction hinges on measuring how fast each wheel is turning and comparing those speeds to the overall vehicle motion. Wheel speed sensors, placed at each wheel, provide real-time rotational data. When braking hard or accelerating on slick surfaces, the wheel that's slipping will spin at a different rate than the others. The system sees this discrepancy and can intervene—reducing brake pressure to a slipping wheel or adjusting engine torque—to regain traction and prevent a skid.

Other sensors don’t track that immediate wheel-to-wheel difference. Temperature sensors monitor heat, not slip. Pressure sensors measure brake line pressure or tire pressure, which aren’t direct indicators of wheel traction. GPS sensors estimate vehicle speed and movement over ground, but they don’t detect wheel-by-wheel speed differences or real-time wheel slip, so they aren’t used to monitor traction on their own.

So, wheel speed sensors are the primary tool for sensing wheel lock or slip and for monitoring traction.