Question 1

An ABS control ECU flashes codes that do not appear in the OEM code chart.Which of the following is the likely cause?
A) PLC connection to tractor is lost
B) modulator valve assembly defective
C) sensor circuit defective
D) ECU defective

Accepted Answer

When an ABS control ECU flashes codes that do not appear in the OEM code chart, it often indicates an issue with the ECU itself, such as a defect or failure. This is because the ECU is responsible for generating and interpreting diagnostic codes. If it is malfunctioning, it may produce incorrect or unrecognized codes.

Question 2

Which of the following accounts for slower modulation frequencies in truck pneumatic brake systems than equivalent hydraulic brake systems?
A) trucks move more slowly than automobiles
B) compressibility of air versus that of hydraulic fluid slows switching frequency
C) truck chassis computers function at slower clock speeds than automobile computers
D) truck ABS system have to manage many more brakes than automobile ABS

Accepted Answer

The compressibility of air, which is used in pneumatic brake systems, versus the incompressibility of hydraulic fluid used in hydraulic brake systems, results in slower modulation frequencies for pneumatic systems. This is because air can be compressed, leading to a delay in the transmission of force through the system, whereas hydraulic fluid transmits force almost instantaneously due to its incompressibility.

Question 3

Technician A says that in a 6S/6M highway tractor ABS,two modules are required to manage the system.Technician B says that a 6S/6M highway tractor ABS is required for most accident avoidance electronics.Who is correct?
A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Accepted Answer

The answer of Technician A says that in a 6S/6M...

Question 4

Technician A says that all ABS circuits are tested during a start-up self test.Technician B says that if all the components checked during an ABS self test are verified functional,the dash ABS light remains illuminated.Who is correct?
A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Accepted Answer

Technician A is correct because ABS systems typically perform a self-test at startup to ensure all circuits and components are functioning properly. If the self-test passes, the ABS light will turn off, indicating all components are verified functional, contrary to Technician B's statement.

Question 5

In a 4S/4M ABS,which wheels have wheel speed sensors fitted?
A) steer axle left,steer axle right,forward drive axle right,forward drive axle left
B) steer axle left,steer axle right,rear drive axle right,rear drive axle left
C) steer axle left,steer axle right,forward drive axle right,rear drive axle right
D) forward drive axle left,forward drive axle right,rear drive axle left,rear drive axle right

Accepted Answer

In a 4S/4M ABS system, sensors are typically fitted on both wheels of the steer axle and both wheels of the forward drive axle to monitor wheel speed and provide optimal braking control.

Question 6

Technician A says that ABS modulation cycle rates are much higher in truck pneumatic brake systems than hydraulic brake systems.Technician B says that ABS pneumatic modulation cycle rates peak at about 7 times per second.Who is correct?
A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Accepted Answer

Technician B is correct because ABS pneumatic modulation cycle rates typically peak at about 7 times per second. Technician A is incorrect as pneumatic systems generally have lower modulation cycle rates compared to hydraulic systems.

Question 7

Which of the following best describes how power line carrier (PLC)multiplexing takes place from a trailer to a tractor?
A) blue auxiliary terminal in a 7-wire trailer connector is dedicated to data bus transactions
B) data is radio frequency (RF)superimposed over the auxiliary hardwire
C) data is pulse width modulated (PWM)from trailer to tractor data bus
D) data is pulse width modulated (PWM)from tractor to trailer data bus

Accepted Answer

Power line carrier (PLC) multiplexing involves superimposing data over existing electrical lines, and in this context, it uses radio frequency (RF) signals over the auxiliary hardwire to transmit data between the trailer and tractor.

Question 8

A current truck or trailer ABS system is required to have FMVSS 121 redundancy.What does redundancy mean in this context?
A) superfluous
B) shuts down if a failure occurs
C) ability to apply brakes immediately when a system fault is detected
D) revert to full pneumatic circuit control in the event of ABS electronic failure

Accepted Answer

Redundancy in the context of FMVSS 121 for truck or trailer ABS systems means that the system is designed to revert to full pneumatic circuit control if there is an electronic failure in the ABS, ensuring that basic braking functionality is maintained.

Question 9

Technician A says that drive axle wheel lock under braking is a major cause of trailer jackknife.Technician B says that even a basic 2S/2M tractor ABS can help reduce jackknife incidents.
A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Accepted Answer

Drive axle wheel lock under braking can indeed lead to trailer jackknife, as it causes the trailer to lose traction and potentially swing out. A 2S/2M (2 sensors/2 modulators) ABS system on a tractor can help prevent this by modulating the brake pressure to avoid wheel lockup, thereby reducing the risk of jackknife incidents.

Question 10

Which of the following ABS configurations can increase the incidence of trailer swing accidents in a semi-trailer rig?
A) no ABS on tractor or trailer
B) ABS on tractor,no ABS on trailer
C) ABS on both tractor and trailer
D) failure of PLC connection

Accepted Answer

When ABS is present on the tractor but not on the trailer, the trailer's wheels can lock up during braking, increasing the risk of trailer swing or jackknife accidents.

Question 11

Technician A says that when the truck brakes are applied,the more severe the braking force,the greater the role played by the front brakes.Technician B says that it is mandatory for current trucks to include the front brakes in the ABS loop.Who is correct?
A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Accepted Answer

The answer of Technician A says that when the truck...

Question 12

When an ABS brake is modulated which of the following is happening?
A) all hold-off air is dumped
B) all service application air is dumped
C) hold-off air is dumped until rate of wheel deceleration normalizes
D) service application air is cyclically dumped until rate of wheel deceleration normalizes

Accepted Answer

ABS (Anti-lock Braking System) modulates brake pressure by cyclically dumping and applying service application air to prevent wheel lock-up, ensuring the rate of wheel deceleration normalizes and maintains traction.

Question 13

Technician A says that trailer ABS fault codes are stored in the controller ECU volatile memory.Technician B says that ABS fault codes can usually be displayed at the controller ECU.Who is correct?
A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Accepted Answer

ABS fault codes are typically stored in non-volatile memory, not volatile memory, so they are retained even when power is lost. Technician B is correct that ABS fault codes can usually be displayed at the controller ECU.

Question 14

In a tandem drive highway tractor with a 4S/4M ABS,which axles are usually monitored and modulated?
A) both tandem drive axles
B) steer axle and rear drive axle
C) steer axle and front drive axle

Accepted Answer

The answer of In a tandem drive highway tractor with...

Question 15

What is the current minimum ABS requirement for a trailer brake system?
A) 2S/1M
B) 2S/2M
C) 4S/2M
D) 4S/3M

Accepted Answer

The current minimum ABS requirement for a trailer brake system is 2S/1M, which stands for 2 sensors and 1 modulator. This configuration ensures basic anti-lock functionality on trailers.

Question 16

Which of the following ABS configurations is most commonly used on tandem drive highway tractors today?
A) two-channel
B) four-channel
C) six-channel
D) eight-channel

Accepted Answer

The answer of Which of the following ABS configurations is...

Question 17

In pneumatic ABS modulation,what happens to air diverted from the service chambers?
A) re-routed to hold-off circuit
B) re-routed to service reservoirs
C) returned to supply reservoir
D) exhausted to atmosphere

Accepted Answer

In pneumatic ABS (Anti-lock Braking System) modulation, the air that is diverted from the service chambers is exhausted to the atmosphere. This process helps in modulating the brake pressure to prevent wheel lockup during braking.

Question 18

How many modulations per second is a typical truck pneumatic ABS capable of managing?
A) less than one
B) up to 3
C) 3 to 7
D) 8 to 20

Accepted Answer

A typical truck pneumatic ABS is capable of managing 3 to 7 modulations per second, allowing it to effectively prevent wheel lockup during braking.

Question 19

Which of the following explains why the 100-tooth reluctor wheel has become standard in truck ABS systems?
A) insufficient voltage can be generated by 16-tooth sensors
B) 3.6-degrees of tire rotation is close to the dynamic footprint of a radial tire at 60 mph
C) computers find it easier to monitor higher frequencies
D) it had to be different from a tailshaft speed sensor

Accepted Answer

The 100-tooth reluctor wheel has become standard in truck ABS systems because 3.6-degrees of tire rotation, which corresponds to the resolution provided by a 100-tooth wheel, closely matches the dynamic footprint of a radial tire at 60 mph. This allows for more precise monitoring and control of the wheel speed, improving the effectiveness of the ABS system.

Question 20

If a fail relay coil ceases to function,which of the following will result?
A) ABS does not function,ABS warning light does not illuminate
B) ABS does not function,ABS warning light illuminates
C) service brakes cannot be applied
D) parking brakes cannot be released

Accepted Answer

When a fail relay coil in an ABS system ceases to function, the ABS will not be able to operate as intended, but the system is designed to alert the driver to this malfunction. This is typically indicated by the illumination of the ABS warning light on the dashboard. The service brakes will still function normally, allowing the vehicle to be stopped safely, and the issue does not affect the operation of the parking brakes.

Quiz 30: Abs and Ebs

An ABS control ECU flashes codes that do not appear in the OEM code chart.Which of the following is the likely cause?

Which of the following accounts for slower modulation frequencies in truck pneumatic brake systems than equivalent hydraulic brake systems?

Technician A says that in a 6S/6M highway tractor ABS,two modules are required to manage the system.Technician B says that a 6S/6M highway tractor ABS is required for most accident avoidance electronics.Who is correct?

Technician A says that all ABS circuits are tested during a start-up self test.Technician B says that if all the components checked during an ABS self test are verified functional,the dash ABS light remains illuminated.Who is correct?

In a 4S/4M ABS,which wheels have wheel speed sensors fitted?

Technician A says that ABS modulation cycle rates are much higher in truck pneumatic brake systems than hydraulic brake systems.Technician B says that ABS pneumatic modulation cycle rates peak at about 7 times per second.Who is correct?

Which of the following best describes how power line carrier (PLC) multiplexing takes place from a trailer to a tractor?

A current truck or trailer ABS system is required to have FMVSS 121 redundancy.What does redundancy mean in this context?

Technician A says that drive axle wheel lock under braking is a major cause of trailer jackknife.Technician B says that even a basic 2S/2M tractor ABS can help reduce jackknife incidents.

Which of the following ABS configurations can increase the incidence of trailer swing accidents in a semi-trailer rig?

Technician A says that when the truck brakes are applied,the more severe the braking force,the greater the role played by the front brakes.Technician B says that it is mandatory for current trucks to include the front brakes in the ABS loop.Who is correct?

When an ABS brake is modulated which of the following is happening?

Technician A says that trailer ABS fault codes are stored in the controller ECU volatile memory.Technician B says that ABS fault codes can usually be displayed at the controller ECU.Who is correct?

In a tandem drive highway tractor with a 4S/4M ABS,which axles are usually monitored and modulated?

What is the current minimum ABS requirement for a trailer brake system?

Which of the following ABS configurations is most commonly used on tandem drive highway tractors today?

In pneumatic ABS modulation,what happens to air diverted from the service chambers?

How many modulations per second is a typical truck pneumatic ABS capable of managing?

Which of the following explains why the 100-tooth reluctor wheel has become standard in truck ABS systems?

If a fail relay coil ceases to function,which of the following will result?