Anti-lock Brake System (ABS) and Vehicle Stability Control (VSC) -general information, trouble codes and component removal and installation
1. The Anti-lock Brake System (ABS) and Vehicle Stability Control (VSC) are designed to maintain vehicle steerability, directional stability and optimum deceleration under severe braking conditions and on most road surfaces. The ABS system is primarily designed to prevent wheel lockup during heavy or panic braking situations. It works by monitoring the rotational speed of each wheel and controlling the brake line pressure to each wheel when engaged. Data provided by the ABS wheel sensors is shared with the VSC electronic control unit (ECU).This very sophisticated system helps with traction control, over/understeering, down hill assist and acceleration control and handling. Another system added to vehicles with VSC is the Electronic Brake Force Distribution (EBD) system. This system works with ABS system applications in accordance with the driving conditions and vehicle load. In addition, when the brakes are applied while cornering, it also controls the braking forces of the right and left wheels, helping to maintain vehicle stability.
General information Actuator assembly
2. The actuator assembly consists of an electric hydraulic pump and four solenoid valves. The electric pump provides hydraulic pressure to charge the reservoirs in the actuator, which supplies pressure to the braking system. The pump and reservoirs are housed in the actuator assembly. The solenoid valves modulate brake line pressure during ABS operation.
Speed sensors
3. The speed sensors, which are located at each wheel, generate small electrical pulsations when the toothed sensor rotors are turning, sending a variable voltage signal to the ABS electronic control unit (ECU) indicating wheel rotational speed.
4. The front speed sensors (see illustration) are mounted on the steering knuckles in close relationship to the toothed sensor rotors, which are integral with the outer constant velocity (CV) joints.
i. 4 ABS front wheel speed sensor location
5. On AWD models, the rear speed sensor is mounted to the rear knuckles. On 2WD models, the sensors are integral with the rear hub and bearing assemblies (see illustration)
i. 5 ABS rear wheel speed sensor location (2WD model)
Yaw rate and acceleration sensor
6. This sensor, which is part of the airbag sensor, relays negative acceleration data to the ABS computer, which uses this information to determine the forward pitch (yaw rate) of the vehicle during panic stops.
ABS and VSC computer
7. The function of the ECU is to accept and process information received from the wheel speed sensors to control the hydraulic line pressure, avoiding wheel lock up and slipping. The ECU also constantly monitors the system, even under normal driving conditions, to find faults within the system. If a problem develops within the system, an «ABS» light will glow on the dashboard. A diagnostic code will also be stored in the ECU, which will indicate the problem area or component. A scan tool is necessary to retrieve the codes.
Diagnosis and repair
8. If the dashboard warning light comes on and stays on while the vehicle is in operation, the ABS system requires attention and the system should be checked for stored trouble codes. Before checking for trouble codes, however, you should perform a few simple checks.
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- Check the brake fluid level in the reservoir.
- Check that all electrical connectors are securely connected.
- Check the fuses.
9. If the above preliminary checks do not rectify the problem, or if any stored trouble codes don’t lead you to the problem, the vehicle should be diagnosed and repaired by a dealer service department or other repair shop.
Components — removal and installation
ABS actuator
10. Disconnect the cable from the negative terminal of the battery (see Engine electrical systems).
Note: Wait at least 90 seconds for the SRS system to deactivate.
11. Remove the air filter housing.
12. Disconnect the ABS electrical connector by releasing the locking lever, then place some rags under the ABS actuator to catch any brake fluid that spills. Using a flare-nut wrench, unscrew the brake line fittings from the ABS actuator (see illustration).
i. 12
12/2012 to 10/2015 ABS actuator brake line positions shown.
NOTE: 10/2015 and later models’ lines 5 and 6 have been reversed
А Electrical connector
1 To Right-front wheel
2 To left-front wheel
3 To right-rear wheel
4 To left-rear wheel
5 From rear connection of the master cylinder
6 From front connection of the master cylinder
Note: It’s a good idea to mark the individual brake lines so you can be sure to put them back into the same position. Use the list provided for reference when reinstalling the brake lines.
Note: 10/2015 and later models the front and rear brake lines to the master cylinder are reversed from the illustration shown (see illustration 12)
13. Remove any brackets securing the brake lines to the ABS bracket, then unbolt the ABS actuator bracket from the body and remove the actuator and bracket as one unit from the engine compartment.
14. Installation is the reverse of removal. Bleed the brake system (see Knock sensor — replacement and testing).
Front wheel speed sensor
15. Loosen the wheel lug nuts, raise the front of the vehicle and support it securely on jack stands. Block the wheels at the opposite end.
16. Remove the inner fender liner (see Body).
17. Follow the sensor wiring harness up to the electrical connector, then unplug the connector.
18. Unbolt the wiring harness securing brackets.
19. Remove the sensor mounting bolt and detach the sensor and bushing from the steering knuckle (see illustration 3.4).
20. Installation is the reverse of removal. Be sure to tighten the sensor mounting bolt to the torque listed in this Chapter’s Specifications. Tighten the wheel lug nuts to the torque listed in the Tune-up and routine maintenance Specifications.
Rear wheel speed sensor
21. Loosen the wheel lug nuts, raise the rear of the vehicle and support it securely on jack stands. Block the wheels at the opposite end.
22. Remove the rear wheel.
23. Remove the rear deck trim side panel (see Body).
24. Disconnect the speed sensor connection and push the grommet through the wheel house along with the speed sensor harness.
25. Follow the speed sensor harness to the harness brackets, then remove the bolts securing the brackets to the vehicle.
2WD models
26. On these models the sensor is integral with the rear hub and bearing assembly. See Suspension and steering for the hub and bearing replacement procedure
AWD models
27. Remove the bolt securing the speed sensor to the rear knuckle.
28. Remove the sensor.
29. Installation is the reverse of removal. Be sure to tighten the sensor mounting bolt to the torque listed in this Chapter’s Specifications. Tighten the wheel lug nuts to the torque listed in the Tune-up and routine maintenance Specifications.