When diagnosing traction control, the ______ system must be working correctly before traction assist can be diagnosed.

• A. Electronic stability program (ESP)
• B. Vehicle speed sensor
• C. Traction control module
• D. Anti-lock brakes (ABS)

Answer: (D)

Traction control relies on monitoring wheel speed and using brake force to prevent wheel slip. The wheel-speed data and the ability to modulate brake pressure come from the anti-lock braking system. If the ABS isn’t functioning, there’s no reliable wheel-speed information and no proper brake-torque control to manage slip, so you can’t accurately diagnose or test traction control. Once the ABS is operating correctly, the traction system has the necessary data and braking control to be diagnosed and evaluated.

The other systems play supporting roles—ESP uses similar inputs to help keep the vehicle stable, but ABS is the foundational element that enables traction control to function and be tested.