Anti-lock Brake System (ABS) — general information
1. The Anti-lock Brake System (ABS) is designed to maintain vehicle steerability, directional stability and optimum deceleration under severe braking conditions and 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 wheel from locking up. The ABS system is primarily designed to prevent wheel lockup during heavy braking, but the information provided by the wheel speed sensors of the ABS system is shared with several optional systems that use the data to control vehicle handling. EBD (Electronic Brakeforce Distribution), varies the front-to-rear and side-to-side braking balance under different vehicle loads. The Trac system controls only the front (driving) wheels, and is designed to automatically adjust front wheel speed when starting or accelerating on slippery surfaces. The VSC system (Vehicle Skid Control) affects your car’s handling during cornering, using information from the ABS sensors and the yaw-rate sensor (which senses the side-to-side tilt of the vehicle). When the skid-control ECU senses oversteer or under-steer, it reduces engine power and selectively applies the brakes.
Components Actuator assembly
2. The actuator assembly is mounted in the right front corner of the engine compartment, and 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 The body contains four valves — one for each wheel.
Speed sensors
3. These sensors are located at each wheel and generate small electrical pulsations when the toothed sensor rings are turning, sending a signal to the electronic controller indicating wheel rotational speed.
4. The front speed sensors are mounted to the front steering knuckle in close relationship to the toothed sensor rings, which are integral with the front drive axle outer CV joints.
5. The rear wheel sensors are mounted to the rear of hub (see illustration). The sensor rings are integral with the rear hub assemblies.
3.5 Typical rear wheel speed sensor location
ABS computer
6. The ABS computer is mounted with the actuator and is the brain of the ABS system. The function of the computer is to accept and process information received from the wheel speed sensors to control the hydraulic line pressure, avoiding wheel lock up. The computer also constantly monitors the system, even under normal driving conditions, to find faults within the system.
Diagnosis and repair
7. If a problem develops within the system, an «ABS» light will glow on the dashboard. If the dashboard warning light comes on and stays on while the vehicle is in operation, the ABS system requires attention and should be examined for stored trouble codes. Before checking for trouble codes, however, you should perform a few simple checks.
- ) Check the brake fluid level in the master cylinder reservoir.
- ) Check that all electrical connectors are securely connected.
- ) Check all the applicable fuses.
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.
Trouble code retrieval
8. The ABS system control unit (computer) has a built-in self-diagnosis system which detects malfunctions in the system sensors and alerts the driver by illuminating an ABS warning light in the instrument panel. The computer stores the failure code until the diagnostic system is cleared or the malfunction is repaired.
9. The ABS warning light should come on when the ignition switch is placed in the ON position. When the engine is started, the warning light should go out. If the light remains on, the diagnostic system has detected a malfunction or abnormality in the system.
10. The codes for the ABS can be accessed by turning the ignition key to the OFF position (engine not running). Install a jumper wire onto terminals TC and CG of the diagnostic link connector and turn the ignition key ON (engine not running) (see illustration). Observe the codes on the ABS warning light or the slip indicator light (on 2012 and later models with vehicle stability control).
3.10 Using a jumper wire between these terminals on the diagnostic connector allows the ABS light to display trouble codes (the connector is located under the driver’s side of the dash)
11. The diagnostic code is the number of flashes indicated on the ABS or slip indicator lights. If any malfunction has been detected, the light will blink the first digit (s) of the code, pause 1.5 seconds, then blink the second digit of the code. For example, a code 34 (left rear wheel sensor) will first blink three flashes, pause 1.5 seconds and blink four flashes. If there is more than one code stored in the ECM, the ECM will pause 2.5 seconds before flashing the next code. If the system is operating normally (no malfunctions), the warning light will blink once every 0.5 seconds.
12. The accompanying list indicates the diagnostic code along with the system specific areas.
13. After the diagnosis check, clear the trouble codes. First, jump terminals TC and CG on the data link connector. Turn the ignition key ON (engine not running) and clear the codes by depressing the brake pedal eight or more times within five seconds. Remove the jumper wire and reinstall the cap on the data link connector. Check the indicated system or component or take the vehicle to a dealer service department to have the malfunction repaired.