Anti-lock Brake System (ABS) — general information Ford F150
General information
1. The Anti-lock Brake System is designed to maintain vehicle steerability, directional stability and optimum deceleration under severe braking conditions on most road surfaces. It does so by monitoring the rotational speed of each wheel and controlling the brake line pressure to each wheel during braking. This prevents the wheels from locking up. The ABS system has taken on a lot more responsibilities than just controlling the brakes during a panic stop. Several different control modules communicate with the ABS controller to maintain vehicle road stability. The following electrical system are all involved in the function of the ABS system.
Electronic Stability Control
2. The Electronic Stability Control (ESC) aids in controlling lateral movement by modulating brake fluid pressure to each wheel.
Hill Descent Control
3. The Hill Descent Control aides in controlling low speed maneuvers down steep grades.
Hill Start Assist system
4. The Hill Start Assist system aides in controlling the vehicle from rolling while stationary on a steep slope. With the system activated, the vehicle will remain in place as you move your foot from the brake pedal and onto the accelerator.
Crash Avoidance System
5. Crash avoidance systems also use the ABS system to apply the brakes when the system is activated.
Trailer Sway Control System
6. Trailer sway control systems use the ABS system to maintain stability when pulling a trailer.
Adaptive Cruise Control System
7. The adaptive cruise control system also utilizes the ABS system to maintain the preset distance from the vehicle in front of you.
Torque Vectoring System
8. The torque vectoring system uses the ABS system to calculate wheel rotation in a turn and adjusts the brake fluid to the front and back brakes in order for the front of the vehicle to hug the inside of the turn better, which improves tire grip.
ABS components
The hydraulic control unit for the Anti-lock Brake System is located in the left-front area of the engine compartment
9. The ABS system has three main components — the wheel speed sensors, the ABS control module and the hydraulic control unit . Wheel speed sensors -located at each wheel, send a variable voltage signal to the control unit, which monitors these signals, compares them to its program and determines whether a wheel is about to lock up. When a wheel is about to lock up, the control unit signals the hydraulic unit to reduce hydraulic pressure (or increase) at that wheel’s brake caliper. Pressure modulation is handled by electrically-operated solenoid valves.
10. If a problem develops within the system, an ABS warning light will glow on the dashboard. Sometimes, a visual inspection of the ABS system can help you locate the problem. Carefully inspect the ABS wiring harness. Pay particularly close attention to the harness and connections near each wheel. Look for signs of chafing and other damage caused by incorrectly routed wires. If a wheel sensor harness is damaged, the sensor must be replaced. Warning: Do NOT try to repair an ABS wiring harness. The ABS system is sensitive to even the smallest changes in resistance. Repairing the harness could alter resistance values and cause the system to malfunction. If the ABS wiring harness is damaged in any way, it must be replaced.
Warning: Repair or removal of either the ABS control module or hydraulic unit must start with the original controller and module in place and the data extracted. If the ABS controller has no communication with the scanner, the factory data (or more commonly called «AS BUILT DATA») will need to be downloaded into the replacement controller. This is something that should be left for either a dealership service department or other qualified repair facility. Caution: Make sure the ignition is turned off before unplugging or reattaching any electrical connections.
Diagnosis and repair
11. If a dashboard warning light comes on and stays on while the vehicle is in operation, the ABS system requires attention. Although special electronic ABS diagnostic testing tools are necessary to properly diagnose the system, you can perform a few preliminary checks before taking the vehicle to a dealer service department or other repair shop.
- Check the brake fluid level in the reser
- Verify that the computer electrical connectors are securely connected.
- Check the electrical connectors at the hydraulic control unit.
- Check the fuses.
- Follow the wiring harness to each wheel and verify that all connections are secure and that the wiring is undamaged.
12. If the above preliminary checks do not rectify the problem, the vehicle should be diagnosed and serviced by a dealer service department or a qualified independent repair shop.
Wheel speed sensor — removal and installation
Front wheel speed sensor
13. Loosen the wheel lug nuts, raise the front of the vehicle and support it securely on jackstands. Apply the parking brake.
14. Remove the front wheels.
15. Remove the brake disc (see Brake disc – inspection, removal and installation).
16. Trace the wiring back from the sensor, detaching all brackets and clips while noting its correct routing, then disconnect the electrical connector.
17. Use compressed air to remove any debris around the speed sensor and mounting bolt.
Location of the front wheel speed sensor
18. Remove the mounting bolt and pull the sensor out from the steering knuckle (see illustration).
19. Installation is the reverse of the removal procedure. Tighten the mounting bolt to the torque listed in this Chapter’s Specifications.
20. Install the wheel and lug nuts, tightening them securely. Lower the vehicle and tighten the lug nuts to the torque listed in the Tune-up and routine maintenance Specifications.
Rear wheel speed sensor
21. Locate the speed sensor and follow the wire harness back to the electrical connector. Disconnect the connector and release the clips holding the wire harness.
22. Use compressed air to remove any debris from around the speed sensor bolt.
Rear wheel speed sensor location
23. Remove the mounting bolt and pull the sensor out .
24. Installation is the reverse of the removal procedure. Tighten the mounting bolt to the torque listed in this Chapter’s Specifications.
25. Install the wheel and lug nuts, tightening them securely. Lower the vehicle and tighten the lug nuts to the torque listed in the Tune-up and routine maintenance Specifications.