HET4 ABS Flashcards
ABS AND AIRBRAKES
What does preventing tire skidding do for the operator?
Allows the operator to steer
Does ABS help a vehicle stay in a straight line?
Yes, helps avoid jacknifing a trailer
Describe Channels
the number of circuits that are modulated
If the governor fails is there another valve to limit air pressure on an air brake system?
Safety valve
What are some negative characteristics of nylon air brake tubing?
it cannot withstand high temperatures, abrasion, wear or excessive movements
What is the advantage of the pilot relay valve over a standard relay valve?
Pilot relay valve has no difference between incoming signal pressure and delivery pressure
In Alberta what is the minimum thickness of brake linings allowed?
The brake lining must be thicker than 8mm or 5/16 inch
When a vehicles weight is doubled, how much more power is required to stop it?
Double
True or False:
Brake lag is normal in an air brake system?
True
If a human can apply and release brakes 1-3 times per seconds, how fast does an ABS system pump the brakes?
up to 100 times a seconds
For an ABS system to perform does every wheel need t have a wheel speed sensor installed?
No, depends on manufacture design
What is needed on the wheel hub to provide ABS?
The tone ring/ tooth wheel/ tooth ring or exciter ring
What type of pulse is being generated to give a signal for the ABS system?
AC pulse
What makes up a wheel speed sensor that works with the tone ring to make up a AC pulse signal?
The speed sensor is a permanent magnet
What is voltage measured in on a vehicle with ABS?
Amplitude
How is frequency measured on an anti-lock braking system?
Hertz
Why is wheel sensor cable length important?
Too long it can become pinched, tangled or damaged
Too short it can stretch and break
What is an air ABS modulator valve is?
Electro-pneumatic output device
List some ABS terms
Electronic Brake system Vehicle dynamic control Vehicle Stability control Automatic traction control Electronic stability control roll stability control
Can ABS correct for operator faults or abnormal/negative conditions?
No
2S/1M translates into?
Two sensors/One modulator
Since when did ABS become mandatory on all new on-highway heavy duty trucks and trailers with air brakes?
March 1, 1998
On a three-axle configuration what system set up will provide maximum protection from flat spotting tires?
six sensor/six modulator (6S/6M)
On a tandem axle trailer, what is the minimum requirement for ABS?
2S/1M (two sensor/one modulator)
True or False
ABS used in normal braking?
False
Does suspension have any affect on braking performance?
Yes, worn suspension can cause poor performance from brakes
1 modulator makes how many brakes pulse on a tandem axle?
Four brakes
Describe Primary and Secondary axles?
Rear axles are considered Primary
Front/Steer axle is considered Secondary
True or False
It is normal for front/steer axles to have spring brakes?
False
Describe an ABS modulator as a valve?
Passive, Normally Open
As speed of tone ring increases, what else increases?
Voltage and frequency
What is the most common ABS system configuration?
4S/4M
Do wheel sensors need to be at a set clearance?
Yes, running clearance needs to be set.
Can an ECU tell the difference between the speed of a wheel and if a wheel is coming loose and moving away from the hub?
Yes due to voltage change vs frequency change
190402d pg 11
If an (AIR) ABS system has one channel, what type of system is it?
2S/1M also the minimum trailer requirement
Define the difference between Truck and Tractor?
Truck - self contained load, carries itself, ie. dumptruck
Tractor - pulls a load, pulls a tailer
On a vehicle with Air suspension, where are the wheel speed sensors usually located?
Usually on the REAR axle
On a vehicle with spring suspension/walking beam, where are the wheel speed sensors usually located?
Usually on the FRONT axle
Do lighter or heavier axles lock up wheels first?
The lighter the axle the more likely the wheels will lock up
Why do we put wheel sensors on different axles on different vehicles?
Depending on suspension styles, one axle will become lighter before the other axles causing it to lock up the wheels faster
After 1998, what is visible to the operator on the dash during start up?
ABS light
During normal operation should the ABS light be on or off?
During normal operation with a correctly working ABS system the light should be off
What type of wiring is run to wheel sensors?
Twisted pairs to reduce interference
What was required after FMVSS121 on-road vehicles?
Spring Brakes, Spring applied - Air released
What two pieces in a ABS valve package with relay valve create the brake modulation?
Electrically operated solenoids and Diaphragm vales
Chatter heard during self diagnostics of an ABS system tell a technician what?
Communication between electronic components
Where does an ECU have be to mounted for an ABS system?
Any location that is protected
True or False
ECUs are always found inside the cab of a vehicle
False
Can debris potentially affect the speed sensory/tone ring communication?
Yes, any metallic particles can affect the spacing of the teeth on the tone ring
What are the three instructions the ECU can give to the ABS valve package with relay valve?
Exhaust
Hold
Reapply
Where is the Tone ring mounted on a vehicle?
On the axle hub
What manipulates voltage being read by speed sensors?
Speed
Proximity
Angle
What information does the ECU need from the speed sensor to decide if information is within parameters?
Voltage and Pulse
Speed sensors can always be referred to as?
Reluctance type
True or False
Heavy duty and Medium duty vehicles have electric brakes?
FALSE
What type of signal is AC?
Analog signal, wave form/ variable
When one wheel slows down faster than other wheels what is it considered?
Wheel Skid
What are the 3 commands from the ECU to the electric solenoids in the ABS valves?
Exhaust
Hold
Reapply
During an ABS event operation, the ECU asks for an EXHAUST from the ABS modulator valve, what position are the solenoids in?
Supply solenoid is activated
Exhaust solenoid is activated
When the ABS modulator valve supply solenoid is energized and exhaust solenoid is de-energized what is the ECU asking from the modulator valve?
To HOLD
holding position
When the ABS modulator is preparing to return to normal brake application supply state what are the electric solenoids states?
Both exhaust and supply solenoid are de-energized
How quickly does an ECU receive and transmit signals?
Milliseconds
What are considered off-board diagnostics?
Scan tool or PC
What is considered on-board diagnostics?
Blink code switch or warning lamp
True or False
The ABS modulator valve sends signals to the ECU?
False, only receives
How many wires run to the modulator?
Three wires, using a common ground
During normal operation of the vehicle what are the ABS modulator solenoids doing?
Nothing, de-energized
On a trailer where is ECU possibly mounted?
On the air reservoir with a relay valve
When arc welding what can prevent damaging the ECU?
Unplugging or disconnecting ECU
Why is the ABS lamp position important?
Due to ABS being apart of driving laws, it needs to be in view of the transport officers
If it is an in the cab warning light, the vehicle operator must be able to see the light
Vehicles with ABS prefer to run tires with circumferences that are within what difference of each other? (inchs)
3/4 inch max differences
What is the purpose of ABS?
To stop tire skid/wheel lock up
With the new green-jacketed trailer cord, and increased wire size, what was the change in voltage drops?
Eliminates voltage drops
PIN/WIRE 7 used to be auxiliary power, what has it become in new equipment with ABS?
ECU. ABS diagnostics from trailer to tractor
PLC stands for?
Power Line Carrier
PRE 1998 7-PIN has what J code?
J560
After March 1998 what J code is used for the 7-PIN connector?
J1939
In an off-road situation, why would ABS be unwanted for decrease braking distance?
Off-Roads that are loose build up in the front wheels when wheels are locked acting as a wedge decreases stopping times
How many bits in a bite?
8 bits in a bite
How many wires are used to communicate ABS?
Two wires, redundant system
True or False:
You must have ABS but Automatic traction control is optional? (Heavy Equipment not automotive application)
TRUE
What are the two ways ATC reduces wheel spin?
- Braking a specific wheel -differential braking
2. Reduces the amount of torque delivered to the drive wheels
Locking a differential can give what?
Traction
Below 40km/h what type of braking does ATC use when needed?
Differential braking
Above 40km/h what is done to combat wheel spin with ATC?
Torque reduction
If differential braking is done above 40km/h what can occur?
Shock loading the driveline and high foundation brake temperatures
How is torque reduction communicated through the vehicle?
Datalink J-1939 between ABS ECU and engine ECU
What are some precautions when working on vehicles with electronics?
- Disconnect the battery/ECU before welding
- Do not disconnect any electrical component with the system powered
- Use only high impedance meters for voltage testing
- Never probe conductor insulation
- Keep excessive heat away from electronic components
If the ATC light is blinking does that mean the ATC is currently activated?
No, the blinking light means the system has been disabled by the operator
Torque reduction is used on what type of engines?
Electronically controlled
Is an ATC valve an input or output device from the ECU?
Output device
What should be released before working on, testing or disabling an ABS system?
Release system air pressure and/or hydraulic brake pressure
What must be done before using a vehicle with ATC on a dynamometer?
The ATC system must be disabled
What are three common ways to disable the ATC system for a dyno test?
Pressing on the blink code switch for at least three seconds
Removing ABS circuit breaker/fuse
Using a scan tool/PC
RSC stands for?
Roll stability control
What systems does the RSC work with to limit the possibility of a rollover condition?
ABS/ATC
What inputs does the ECU of the RSC system need to make decisions?
Wheel Speed Sensors
Lateral/side to side movement - plots lateral acceleration limit (accelerometer)
What does the RSC system use to slow the vehicle?
Reduces engine torque
Engage engine/driveline retarders
Apply brake pressure to the drive axle brakes (from ATC valve)
Modulate brake pressure to the trailer brakes
Which wheels receive the most braking force, to avoid a roll over?
The wheels that bear the heavier loads
What must be done to take an RSC system to an ESC system?
Add components - ESC module
Front axle control valve
Steering angle sensor (SAS)
Brake demand pressure sensor
What conditions can an ESC system prevent?
Jackknife or drift-out condition
ESC stands for?
Electronic stability control
An advanced ECU that monitor many different functions uses what SAE J systems?
J1708/J1587, can communicate with tractor J560
The SAS gets its input from?
The operator
SAS stands for?
Steering angle sensor
What is inside the ESC module to understand conditions?
Yaw Sensor and Accelerometer
The Yaw sensor inside the ESC module measures what?
Rotational forces - detects jackknifing/spin out
The accelerometer inside the ESC module measures what?
Lateral acceleration during cornering
What does the ESC module communicate with?
ABS ECU
What should be done when troubleshooting air ABS issues?
- Talk to the operator
- Check basic service brake system
- Visually inspect ABS components
- Operate the vehicle confirm problem and test ABS system operation
- Contact the equipment manufacturer’s tech support
What is the easiest way to confirm warning lamp/indicators work?
When the key is first turned to on, all lamps should illuminate
What is the normal resistance reading from a wheel speed sensor to the ECU?
500 - 2000 ohms
What can excessive wheel bearing end play result in?
erratic wheel speed sensor readings
How are the exhaust and supply solenoids tested on an ABS modulator control valve assembly?
With power disconnected, check the resistance of the solenoid from ground terminal to circuit terminal.
12V system - 4-8 ohms
24V system 8-16 ohms
make sure to clean contacts before testing
pg 21 190402e
Americans follow FMVSS 121 what is the Canadian counter part?
CMVSS 121
Channels refers to?
Modulators
What types of road conditions does the RSC work in?
Dry, good road conditions
What type of road conditions does the ESC system work in?
Wet/Slippery Road conditions
True or False:
If there is a fault in the ABS system the foundation brakes will not work?
False
Where is the ATC valve located in the air circuit of the truck?
Between the treadle valve (primary) and service brake relay
Before removing wheels what should be checked for play?
The wheel bearing adjustment, end play
Before removing air lines what should be done to the system?
Air system should be drained
What is the purpose of dielectric grease when using it on electrical connections?
To help prevent moisture from entering the cavity during normal operation
True or False:
ABS on a hydraulic brake system can correct for operator faults?
False
Why is DOT 5 brake fluid not recommended for brake systems with ABS?
The fluid does not absorb moisture and retains tiny air bubbles
If there is damage in the ABS modulator valve, can it affect normal hydraulic brake action?
Yes, I.e. Internal valve is jammed closed
190402f pg 15
How many solenoid valves are needed for each wheel location?
One inlet and one outlet
What is the best way to repair an ABS harness?
Manufactures recommendation or replace
When mounting a hydro-boost power brake what needs to be inspected?
An air gap/pedal play
To avoid Brake Drag
Metering Valve purpose is?
Brake Timing, apply rear brakes first
Proportioning valve does what to a disc and drum hydraulic brake system?
Blocks the line to the drum since they self energized
What suspension component can affect braking ability?
Worn/broken shock absorber
What is the operators complaint when the brake fluid is low?
Spongy brakes, air is now in the system
Where is the ATC valve is located?
Between the brake treadle valve and service brake relay at the REAR drive axle(s)
How is an ECU grounded?
Through a dedicated ground
In a normal braking event what is the ABS modulator valve doing?
Nothing, both solenoids are de-energized and allows air to flow through supply port to delivery port
In an ABS event operation what is the valve doing with both solenoids energized?
Air coming in the supply port cannot exhaust or go through delivery port, and air from delivery side can exhaust
When the ABS valve is HOLDING what is happening inside the valve?
Supply air is trapped inside the valve and the delivery side cannot exhaust
Where is the ABS modulator valve located on the system?
Between relay valve and brake chamber (pot)
What type of wires are used in the ABS system?
Twisted Pairs
Shielded wires
True or False:
All ABS components are serviceable?
FALSE
When bleeding a hydraulic brake system with ABS, is there most likely a pattern to follow?
Yes
What is the general range of waveforms from speed sensors/tone rings?
0-400Hz
What can a tone ring be safely heated to before installing?
121°C (250°F) in boiling water or over
What does water in brake fluid cause?
Lower Boiling point
What could give you a false diagnosis of an ECU you believe was faulty?
Aftermarket radio transmission devices installed on the vehicle - if too close to ECU or ABS control module
What causes brake fade?
Excessive heat
After servicing a wheel hub on a vehicle with ABS what will need to be done?
Reset the speed sensor depth
Does an engine exhaust brake, ie. tier 3, have enough braking power to cause a wheel lock up?
Yes, some ABS systems will auto turn off engine brakes
What is the best way to test an ECU?
using a break out box
In an ABS system what uses pulse generator principle?
Wheel speed sensor
When does an ABS ECU only monitor wheel speeds?
During a non-skiding brake application
