Anti-lock Brake System (ABS), Traction Control (TCS) and vehicle stability control (StabiliTrak) systems — general information

1. The Anti-lock Brake System (ABS) helps to maintain vehicle maneuverability, directional stability, and optimum deceleration under severe braking conditions on most road surfaces. It does so by monitoring the rotational speed of the wheels and controlling the brake line pressure to the wheels during braking. This prevents the wheels from locking up on slippery roads or during hard braking.

Electro-Hydraulic Control Unit (EHCU)

2. The Electro-Hydraulic Control Unit (EHCU), mounted on the left-side frame rail underneath the cab, controls hydraulic pressure to the brake calipers by modulating hydraulic pressure to prevent wheel lock-up (see illustration). It is made up of the Brake Pressure Modulator Valve (BPMV) and the Electronic Brake Control Module (EBCM). Basically, the BPMV reduces pressure in a brake line when the Electronic Brake Control Module (EBCM) detects an abnormal deceleration in the speed of a wheel (via a wheel speed sensor signal). When the speed of the wheel is restored to normal, the modulator once again allows full pressure to the brake. This cycle is repeated as many times as necessary, which results in a pulsing of the brake pedal.

3.2 The ABS Electro- Hydraulic Control Unit (EHCU) is located along the left frame rail, underneath the driver

Chevrolet Silverado Brakes _ The ABS Electro- Hydraulic Control Unit (EHCU) is located along the left frame rail, underneath the driver

3. In addition to sensing and processing information received from the brake switch and wheel speed sensors to control the hydraulic line pressure and avoid wheel lock up, the EBCM also continually monitors the system and store’s fault codes which indicate specific problems.

Note: Brake fluid bleeding for the ABS control unit is only accomplished with the use of the proper type of scan tool.

Traction Control System

4. Some models are equipped with a Traction Control System (TCS). When wheel slip is detected, the Electronic Brake Control Module (EBCM) will activate the traction control mode. A signal is sent from the EBCM to the PCM (Powertrain Control Module) commanding less torque to the drive wheels. Torque is reduced by retarding the ignition timing and by controlling the throttle control actuator (TCA).

5. The Traction Control System (TCS) is deactivated when the transmission shift lever is selected into the Low position, the driver manually selects Off on the TCS switch on the dash or the EBCM automatically shuts off the TCS during cruising or non-hazard conditions.

Stability Control System

6. Some models may be equipped with Sta biliteracy, a stability control system. This system is designed to assist in correcting over/ under steering. This system is integrated with the ABS and TCS systems but uses additional sensors.

Wheel speed sensors

7. Generally, there is a wheel speed sensor designated for each wheel. Each sensor generates a signal in the form of a low-voltage electrical current or a frequency when the wheel is turning. A variable signal is generated as a result of a square-toothed ring (tone-ring, exciter-ring, reductor, etc.) that rotates very close to the sensor. The signal is directly proportional to the wheel speed and is interpreted by an electronic module (computer).

8. The front sensors are mounted to the hub and wheel bearing assemblies and the tone-rings are integrated within the assemblies (see illustration).

3.8 Front wheel speed sensor location

Chevrolet Silverado Brakes _ Front wheel speed sensor location

9. The rear sensors are mounted to the rear axle housing. The tone-rings are integrated with the rear axle shafts (see illustration).

3.9 Rear wheel speed sensor location

Chevrolet Silverado Brakes _ Rear wheel speed sensor location

Warning lights

10. The ABS system has self-diagnostic capabilities. Each time the vehicle is started, the EBCM runs a self-test. There are two warning lights on the instrument panel, a red BRAKE light and an amber ABS light, each with their own functions. During starting, these lights should come on briefly then go out. If the red BRAKE light stays on, it indicates a problem with the main braking system, such as low fluid level detected or the parking brake is still on. If the light stays on after the parking brake is released, check the brake fluid level in the master cylinder reservoir (see Tune-up and routine maintenance).

11. The amber ABS light indicates a problem with the ABS system, not the main or basic brake system. If the light stays on, it indicates that there is a problem with the ABS system, but the main system is still working. Take the vehicle to a dealer service department or other qualified repair shop for diagnosis and repair.

Diagnosis and repair

12. If a dashboard warning light comes on and stays on while the vehicle is in operation, the ABS, or other related systems require attention. Information will also be displayed in the Driver Information Center (DIC), as equipped. Although special diagnostic testing and tools are necessary to properly diagnose the system, you can perform a few preliminary checks before taking the vehicle to a dealer service department.

a) Check the brake fluid level in the reservoir.

b) Check the electrical connectors at the EBCM and the hydraulic modulator/ motor assembly.

c) Check the fuses.

d) Follow the wiring harness to each wheel and verify that all connections are secure and that the wiring is undamaged.

13. If the above preliminary checks do not rectify the problem, the vehicle should be diagnosed by a qualified repair shop due to the complexity of this system. All actual repair work must be done by a qualified/certified automotive technician.

Warning: Do NOT try to repair a wheel speed sensor wiring harness. These systems are sensitive to even the smallest changes in resistance. Repairing the harness could alter resistance values and cause the system to malfunction. If the wiring harness is damaged in any way, it must be replaced.

Note: Make sure the ignition is turned off before unplugging or reattaching any electrical connections.

Wheel speed sensor — removal and installation

Warning: The dust created by the brake system is harmful to your health. Never blow it out with compressed air and don’t inhale any of it. An approved filtering mask should be worn when working on the brakes. Do not, under any circumstances, use petroleum-based solvents to clean brake parts. Use brake system cleaner only!

14. Loosen the wheel lug nuts, raise the vehicle and support it securely on jack stands. Remove the wheel.

15. Make sure the ignition key is turned to the Off position.

16. If you’re replacing a front sensor, remove the front brake disc (see Brake disc — inspection, removal and installation).

17. Remove the mounting fastener and carefully pull the sensor out from the front hub assembly or the rear axle housing (see illustrations 3.8 and 3.9).

18. Follow the wiring harness to the electrical connector and disconnect it. Remove the harness from any brackets that may secure it to other components.

19. Installation is the reverse of the removal procedure. Tighten the mounting fastener to the torque listed in this Chapter’s Specifications.

20. Install the wheel and lug nuts, lower the, vehicle and tighten the lug nuts to the torque listed in the Tune-up and routine maintenance Specifications.

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