The anti-lock braking system (ABS) and Traction Control systems in your Grand Prix both use the ABS wheel-speed sensors and modulator valve assembly to control wheel slip. The ABS system monitors the wheel-speed sensors and relieves brake pressure on a wheel that it senses is nearing lock-up. The Traction Control system monitors the same wheel-speed sensor and applies brake pressure to any wheel it senses over accelerating. Diagnosis of these systems is accomplished using a scan tool and the car’s on-board computer diagnostics function.

Step 1

Check the tires for proper wheel size and check the fluid level in master cylinder. Improper tire size, such as two different sizes, will cause the wheels to turn at different speeds and may set a false code when the computer senses this as potential wheel lock-up. Low fluid level in the brake master cylinder will result in shutdown of the ABS and Traction Control system to prevent introduction of air into the brake system.