402f Hydraulic ABS

Question 1

Briefly identify three (3) main types of hydraulic antilock brake systems.

Answer 1

• Rear wheel antilock only.
• Rear wheel and individual front antilock, 3-channel.
• Individual front and rear antilock, 4-channel.

Question 2

Identify the major components of a four-channel antilock brake system.

Answer 2

• Electronic control unit (ECU).
• Wheel speed sensors and tone rings.
• Modulator valve/solenoid control valve assembly.
• ABS warning light.

Question 3

Explain how the wheel speed sensor and tone ring work together to send a signal to the ECU.

Answer 3

The wheel speed sensor creates a magnetic field. As each tooth on the tone ring passes the sensor, the magnetic field is interrupted. This pulse is sent to the ECU as a frequency signal.

Question 4

Explain the basic purpose(s) of the antilock brake system modulator valve assembly.

Answer 4

The modulator valve assembly receives a signal from the ECU to decrease, increase or maintain brake pressure to individual wheel brakes.

Question 5

Explain the main purpose of the ABS electronic control unit.

Answer 5

During an emergency braking situation, the ECU receives signals from wheel speed sensors and sends signals to the modulator valve assembly. This prevents wheel lock-up while maintaining steering control.

Question 6

An ABS indicator warning light can be used for diagnostic purposes.
T/F

Answer 6

true

Question 7

A hydraulic ABS system is used with a hydraulic-over-hydraulic basic brake system.
T/F

Answer 7

true

Question 8

Identify the two (2) types of hydraulic brake fluids that are recommended for use with antilock brake systems.

Answer 8

• DOT 3.

- DOT 4.

Question 9

Identify the type of hydraulic brake fluid that is not recommended for use in an antilock brake system.

Answer 9

DOT 5 (or silicone-based brake fluids).

Question 10

When the operator turns the ignition ON, the ABS indicator warning light will remain off unless a problem exists within the antilock brake system.
T/F

Answer 10

false; The ABS light comes on momentarily as part of a system self-test and then goes out if no problems exist in the ABS system.

Question 11

The ABS indicator warning light will only display ABS fault codes.
T/F

Answer 11

false; The indicator light will also do a bulb check on engine start-up. Some ABS indicator lights are used to monitor brake fluid level in the master cylinder.

Question 12

Explain how a wheel speed sensor and a tone ring are able to produce a wheel speed signal.

Answer 12

As an electrical current flows through the wheel speed sensor, a magnetic field is created around the end of the sensor. As each tooth on the rotating tone ring passes in front of the sensor, the magnetic field is interrupted. The disrupted magnetic field produces a voltage waveform signal that is interpreted by the ECU as a particular speed.

Question 13

Voltage waveforms created by the speed sensor and tone ring may range from 0 to 400 Hz. A voltage of 100 Hz would be interpreted by the ECU as a slowly rotating wheel.
T/F

Answer 13

true

Question 14

The only function of an ABS electronic control unit is to transmit signals to other electronic components.
T/F

Answer 14

false; The ECU also receives signals from other ABS components.

Question 15

The functions(s) of an ABS modulator valve assembly include:

Answer 15

Receiving signals from the ECU.

Question 16

Fault codes identified as active indicate a past problem that existed within the ABS.
T/F

Answer 16

false; Active codes indicate an immediate problem.

Question 17

In order to fully diagnose and test the ABS, the vehicle must always be secured with the parking brake fully applied.
T/F

Answer 17

false; Some tests are done when the wheels are moving. The vehicle must be securely supported on jack stands.

Question 18

When you first activate the ABS indicator light, you could gain the following information.
(3)

Answer 18

• The ABS is functioning normally.
• An active fault code can be indicated.
• A stored fault code can be revealed.

Question 19

Prior to testing an ABS, some preliminary system/vehicle checks should be conducted. Identify three (3) checks you would do before beginning a testing process.

Answer 19

• Check the master cylinder fluid level and condition.
• Check the battery voltage and compare it to specs.
• Ensure that the vehicle is secured or on stands for the appropriate tests.
• Check for visible external ABS damage.

Question 20

The ignition switch must be placed in the ON position before conducting most ABS tests with a DMM.
T/F

Answer 20

false; Some tests are performed with the ignition switch in the OFF position.

Question 21

When you disconnect or reconnect an ABS electronic control module or any type of electronic module, you must have the ignition switch in the OFF position.
T/F

Answer 21

true

Question 22

All ABS components should always be dismantled in case you are able to repair them and return them to service. This can save the customer considerable money.
T/F

Answer 22

false; Some ABS components are non-serviceable. These components are left intact and replaced as a unit.

Question 23

Prior to bleeding an antilock brake system, you must depressurize the hydraulic brake system. Explain how you would do this so that you would not be injured by high-pressure brake fluid.

Answer 23

Turn the ignition switch to the OFF position. Pump the brake pedal at least 30 times or more as instructed in the service manual. Ensure that the brake pedal has increased resistance after this process is completed.

Question 24

The brakes must be bled in a pattern. The ABS modulator valve assembly may also have a bleeder screw. It must also be included in this pattern.
T/F

Answer 24

true