Hydraulic Antilock Brake Systems

Question 1

Briefly identify three main types of hydraulic antilock systems.

Answer 1

a. rear wheel antilock only.
b. rear wheel and individual front anti lock 3 channel.
c. Individual front and rear antilock 4 channel.

Question 2

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

Answer 2

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 3

Explain the main purpose of the ABS electronic control unit.

Answer 3

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

Question 4

A hydraulic ABS system is used with a hydraulic over hydraulic basic brake system.
True
False

Answer 4

True

Question 5

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

Answer 5

DOT 5 silicone brake fluid

Question 6

The ABS indicator warning light will only display ABS fault codes.
True
False

Answer 6

False, bulb checks. Also monitors brake fluid level.

Question 7

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

Answer 7

True

Question 8

The function of an ABS modulator valve assembly include:

a. transmitting signals to the ECU.
b. receiving signals from the ECU.
c. transmitting signals to the wheel speed sensors.
d. receiving signals from the wheel speed sensors.

Answer 8

b. receiving signals from the ECU.

Question 9

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

Answer 9

False. Some tests require the wheels rotating.

Question 10

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

Answer 10

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.

Question 11

When you disconnect or re-connect and ABS electronic control module or any type of electronic module you must have the ignition switch in the off position.
True
False

Answer 11

True

Question 12

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.
True
False

Answer 12

False, some are not serviceable.

Question 13

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.
True
False

Answer 13

True

Question 14

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

Answer 14

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

Question 15

Explain the main purpose of the antilock brake system modulator valve assembly.

Answer 15

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

Question 16

An ABS indicator warning light can be used for diagnostic purposes.
True
False

Answer 16

True

Question 17

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

Answer 17

Dot 3

Dot 4

Question 18

When the operator turns the ignition on, the ABS indicator warning light will remain off unless a problem exists within the anti-lock brake system.
True
False

Answer 18

False, light will come on for self test and when the system activates.

Question 19

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

Answer 19

As electrical current flow 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.

Question 20

The only function of an ABS electronic control unit is to transmit signals to other electronic components.
True
False

Answer 20

False, also receives.

Question 21

Fault codes identified as active indicate a past problem that existed within the abs.
True,
False

Answer 21

False inactive.

Question 22

When you first activate the abs indicator light, you could gain the folllowing information.

a. The ABS is functioning normally.
b. An active fault code and be indicated..
c. A stored fault code can be retrieved.
d. high brake fluid level in the master cylinder reservoir.
e. all of the above.

Answer 22

e. all of the above.

Question 23

The ignition switch must be placed in the on position before conducting most ABS tests with a DMM.
True
False

Answer 23

False

Question 24

Prior to probing any connector pin with a DMM, you must:

a. set the meter to the correct test.
b. clearly identify the connector pins that will be probed.
c. set the meter for the correct scale.
d. Turn the ignition switch to the off position unless instructed otherwise instructed by the service manual.
e. do all the above responses.

Answer 24

e. all responses are correct.

Question 25

Prior to bleeding and antilock brake system, you must depressurized the hydraulic brake system. Explain

Answer 25

Turn the ignition switch to the off position. Pump the brake pedal 30 times or more. Ensure the brake pedal has increased resistance.