When inspecting the key condition, what should you look for?
Inspect the vehicle keys for wear, nicks, bends, or other damage.
When inspecting the ignition switch, what should you ensure
Ensure that the ignition switch is securely mounted and operates smoothly without binding and provides constant port a the accessory, on, and crank positions.
I the truck is equipped with a push-button start switch, how should it operate?
It should operate easily without sticking while properly closing the cranking circuit when depressed.
What is a driver ID code or card used for?
It is used with trucks that have a keyless ignition system
Describe the earlier lamps or indicator lights.
Earlier lamps were small, round lights that were color-coded for their system; yellow for a warning or caution in a non-safety-related system and red for safety-related system warnings.
What systems still use lights?
Major or Safety related systems.
What kind of lights do many non-safety systems use?
Light Emitting Diodes (LED) behind a pictogram of the system it is monitoring.
Why are LED lights such an improvement?
This improvement allows for less electrical current usage in the instrument panel and more reliable operation.
What are the benefits of the self-check feature?
It illuminates all warning lamps when the ignition switched first switched to the on position.
This lets the driver and/or technician know that the lamp and circuit are operational.
What are alarms and buzzers used for in some systems?
For low-pressure (which is mandatory) and for low oil pressure.
The low pressure must sound when the system air pressure drops in below 50 percent of the governor cut-out pressure (approximately 60 psi)
When checking the operation of instruments/gauges and panel lighting, what will a short circuit in the sending unit wire to the gauge do?
It will lower resistance in that circuit, causing the gauge needle to read high.
What will a short circuit to ground in a sending unit wire cause?
It will cause an overload of current to the gauge, which will burn out in a very short time.
Although not considered an official criterion for out-of-service (OOS) status what will a malfunctioning oil pressure gauge cause?
It may be cause for an inspector to deadline a vehicle because a no-oil pressure condition can rapidly destroy and engine.
In performing a proper and thorough check of a vehicle’s instrument panel, as a part of any PMI, what happens when the ignition is first turned on?
Electronic gauges perform a self-test by sweeping the needles.
What does PTO stand for?
Electronic Power Take-Off
How do modern diesel engines mange idle speed and shutdown?
By computer control. This is sometimes a PTO function when the engine speed is set to operate auxiliary equipment.
How can idle speed be raised and lowered?
By the use of a toggle switch provided on the dash.
How does a programmed engine shutdown occur?
After the desired time interval, when the desired time has elapsed, without input from the throttle pedal of the clutch pedal, the engine will shut down automatically.
What would you use to change the programmed time?
An electronic service tool. (EST)
How does the automatic stop/start features work?
Most engine management Systems have stop/restart features that expand the normal idle shutdown feature to further reduce idle time.
They will automatically stop and restart when require to hold engine temperature about a programmed specific value, maintain the battery charge level, and to keep the cab/sleeper at a temperature level programmed into customer parameters.
What are other benefits of having automatic stop/start features?.
Other benefits claims are reduced emissions, noise, and engine life.
What conditions must be in order for the stop/restart feature to be enabled?
- One OEM system requires that the ignition switch be on, the engine idling with the idle shutdown timer enabled, the hood closed, the transmission in neutral or park, the parking brake set, and the master cruise switch in the on position.
What happens when the system determines to start the engine?
Based on sensor inputs, the active lights illuminates and an alarm in the engine compartment sounds, and the engine cranks.
If the engine fails to start, will a second attempt occur?
Yes, a second attempt will occur in 45 seconds.
At startup, how many RPMs does the engine ramp up to?
1,000 RPMs
What happens if the restart is prompted by input from the cab temperature sensors?
After about 30 seconds, the climate control system will turn on to manage the cab/sleeper temperature.
Engine shutdown can also occur to prevent damage to the engine from lack of lubrication or overheating conditions.
What is Failure Strategy?
The way in which the engine electronically responds to a potentially damaging conditionally
1. Failure strategy response levels are programmable and typically would be driver alert-(lowest level), engine ramp-down and engine shutdown -(highest level)
What level of failure strategy do manufacturers recommend programming?
The highest level failure strategy, except for emergency vehicles, such as fire trucks are programmed with low-level failure strategy. An EST can be used to check the programmed failure response.
When checking the HVAC system, what should it be able to do?
The HVAC system should be able to regulate the temperature in the cab and sleeper.
What should the blower motor be able to do?
The blower motor should operate at all speeds.
What should the blower be able to do?
The blower should produce an adequate flow of air and should not be abnormally noisy.
What should the technician hear with the engine idling and what are the steps he should take?
- With the engine idling, the tech should hear the A/C compressor clutch engage when air conditioning is selected.
- Raise the engine to about 1,500 rpm and close the doors and windows.
- Turn the blower to high and select the coldest temperature.
- Run the system for about 10-15 minutes and compare the temperature of the air at the outlet nearest the evaporator with specifications in the service manual.
- Check the sleeper controls the same way.
If the truck has an ATC, what should the outlet temperature be?
The outlet temperature should be within several degrees of the set temperature.
What cab and chassis accessories should be tested during a road test.
A vehicle onboard radar (VORAD) collision warning system (CWS) has to be tested on the road as well as with an EST.
What is the typical process for checking DTCs?
Use a handheld EST of a laptop computer to access the data bus; then check for, record, and clear DTCs.
What are the DTCs controlled and monitored by?
Electronic modules.
What is used to facilitate troubleshooting intermittent problems that either do not generate codes or do not store a code without a clear reason?
Most systems will accommodate a snapshot readout from the electronic control module (ECM) to facilitate troubleshooting intermittent problems that either do not generate codes or do not store a code without a clear reason.
What do control modules store?
Control modules store fault doces against parameter identifications (PIDs)
How does the technician access the databus?
To access the databus, the technician connects a diagnostic reader to the American Trucking Association (ATA) connector.
Once the diagnostic reader is connected, what will most systems allow two-way communications for reading?
Most systems allow two-way communications for Reading system parameters, calibration data, diagnostics, data programming, recalling faults, and audit trails.
How do some electronic systems display active codes?
By blinking two-digit numerals on the instrument panel indicator.
Diagnostic tests are menu-driven, so what should they be used to identify?
To identify the FMIs (Fault Mode Indicators).
Once the problems have bee corrected, what should be done with the inactive fault codes?
The inactive fault codes need to be cleared. ESTs can be used to clear these codes.
What are ESTs capable of reading the chassis databus connected to?
ESTs capable of reading the chassis databus are connected to the on-board electronics by means of an SAE/ATA J1587/J1708/1939 6 pr 9-pin Deutsch connector in all current systems.
What do the 6 or 9 in Deutsch connector and the adherence by the engine electronics OEMs to SAE
databus software protocols enable?
It enables proprietary software of one manufacturer to at least read the parameters and conditions of its competitors.
This means that if a Caterpillar-powered truck has an electronic failure in a location where the only service os for a Detroit Diesel Corporation (DDC), some basic problem diagnoses can be undertaken using the DDC electronic diagnostic equipment.
Describe On-board diagnostic ESTs.
On-board diagnostic lights blink or flash codes (OEMs use both terms) are an onboard means of troubleshooting using a dash or ECM mounted electronic malfunction light or check engine light (CEL). Normally only active codes (ones indicating malfunction at the time of reading) can be read in truck (engine) ECMs but some will read historic codes.
Describe scanner ESTs.
Scanners are read-only tools capable of reading active and historic or inactive (logged but not currently indicating a malfunction) codes and sometimes system parameters, but little else. They are obsolete as a truck/bus diesel engine.
Describe Generic reader/programmer ESTs.
Generic Reader/programmers are microcomputer-based ESTs designed to read and reprogram all proprietary systems in conjunction with the appropriate software cartridge or optical card. They are usually tough and portable. The Prolink 9000 has become the industry standard.
Describe Proprietary ESTs.
Proprietary ESTs are usually PC-based test instruments packaged by the OEM for use exclusively on their system. They have the advantage of offering an optimum degree of user-friendliness and the disadvantage of being system-specific and high cost. Examples are:
Cummins: Compulink, Echwxk, INSITE.
Cat: Electronic Tehnician (ET)
DDC: Detroit Diesel Diagnostic Software
What does SAE J1587 cover?
SAE J1587 covers common software databus protocols in electronic systems.
What does SAE J1708 cover?
SAE J1708 covers common hardware protocols.
What does SAE J1939 cover?
SAE J1939 covers both hardware and software protocols. The acceptance and widespread usage of these protocols enables the interfacing of electronic systems manufactured by different OEMs on truck and bus chassis, plus permits any manufacturer’s software to at least read other OEMs’ electronic systems.
When should the operation of electric and air horns be checked?
They should be tested during the driver’s pre-trip and post-trip inspections.
When checking the condition of safety equipment, what is the necessary safety equipment should the truck be equipped with?
The truck should have spare fuses (unless equipped with circuit breakers), three red reflective triangles, and a properly charged and rated fire extinguisher within arm’s reach of the driver’s seat. Flags, lanterns, and flags are optional.
CVSA calls for deadlining when?
When safety devices such as chains and hooks have been repaired improperly.
When do federal regulations prohibit the usage of a vehicle?
Federal regulations prohibit the usage of a vehicle that does not have at least one light illuminated for loads projecting more than 4 feet beyond the vehicle.
What should be the condition of rear chains and hooks that are used in double trailer systems for a hookup?
Rear chains and hooks that are used in double trailer systems for a hookup should not be worn to the extent of a measurable reduction in link cross-sectional area or have any significant abrasions, cracks, or other faults that would affect structural integrity. If any defects are found, then deadline the vehicle.
How do you check the operation of all seatbelts and restraints?
With the seat belt on and the truck moving, activate the parking brake to brake the truck very quickly and determine if the seat belt inertia reel locks. Visually inspect seat belt anchors, seat bolt downs, and sleeper bunk harnesses.
How would you check the supplemental restraint system (SRS)?
When the key is turned on the SRS performs a self-test. You should observe that the SRS or airbag indicator light illuminates and stays on for several seconds following startup, then extinguishes. If it stays on continuously or blinks, there is a problem in the system that needs correction,
How should you check wiper blades and arms?
The blade should remove water from the entire sweep area. Replace the blade if the rubber is cracked, separated, has segment missing, or is stiffened with age and cannot properly clear the windshield. The arm attaches securely to the wier mechanism and provides the correct tension for the wiper blade to the windshield. contact.
How should you check wiper and washer motor operation?
Check electric wiper motor operation through all speeds and delay settings. If any speeds are inoperable, follow the manufacturer’s service procedures to identify the failed component and its replacement procedures.
What additional checks should be used for air-operated wiper motors
Sir-operated wiper motors should be checked as with other wiper motors but with additional checks for air leaks.
Adjust the arm to sweep and park in the correct areas and not contact the cabin in any position.
How should the washer fluid be checked?
Inspect the container for debris. Ensure that the correct washer fluid is in use for the season and conditions that the vehicle is operating under. Check the condition and aim of the spray nozzles and perform necessary adjustments or replace defective parts.
What do the CVSA safety standards regarding wiper and washer operation?
CVSA safety standards out-of-criteria state that any wiper unit that has inoperable parts or missing wipers that render the system ineffective on the driver’s side shall cause for deadline.
How will the majority of trucks or truck-trailer combinations weighing more than 26,000 pounds be registered?
Under the Intentional Registration Plan (IRP)
A cab card is issued to the vehicle stating the IRP areas in which the vehicle is allowed to operate.
What must each vehicle as proof that an inspection was completed?
The Highway Administration has set up a minimum inspection standards program.
Proof can either be a copy of the inspection form kept on the vehicle or a decal.
If using a decal, a copy of the inspection form must be kept on file and must indicate where the inspector can get a copy.
Is the tractor/trailer considered to be two vehicles?
Yes, and each requires a decal. A converter dolly is a separate vehicle.
What information must the decal show?
Date vehicle passed inspection, name, and address to contact concerning inspection records and the VIN.
What, regarding the windshield will take a vehicle out of service by the commercial CVSA out-of-service standards?
Any crack over 1/4 inch wide, intersecting cracks, discoloration, or other vision-distortion matter in the sweep of the wiper on the driver’s side.
What does the leveling valve do in the cab air seat?
The leveling valve maintains the proper air pressure in the air springs to provide the correct seat height.
What does an air-suspended seat do?
An air-suspended seat reduces road shock transferred through the chassis, cab, and seat to the driver.
Air pressure is supplied to the air-suspended seat through a pressure protection valve and a regulator.
What do the Department of Transportation’s Federal Motor Carrier Safety Regulations and the CVSA standard inspection procedures require in regard to the inspection procedures?
A fault such as a loose mirror mounting is always recorded on a PMI.
There should be no blemishes on the mirror glass.
If the truck uses either heated or motorized mirrors when the mirror heat switch is on, an indicator light should be on, and the mirror surface should become warmer than room temperature.
What is a driver’s check good for?
Checking the vehicle area for hazards on the vehicle such as dents or cracks, using a visual and hands-on inspection
What should you use to lubricate all cab and hood grease fittings?
Use light machine oil and a lithium-based grease on hinges and latches.
Knowing that most current cabs use air ride, what should you check when inspecting cab mountings, hinges, latches, linkages?
Check the foreword pivots for wear and excessive movement; check the ride height and leveling valve, insect shock absorbers for leakage.
Visually and dynamically test the bushings.
How many circuits are there with most hydraulic cab lift systems and what are they?
There two circuits: the push circuit that raises the cab from the lowered position to the desired tilt position and the pull circuit that brings the cab from a fully tilted position up and over the center.
What should you inspect the hydraulic cylinders for?
Hydraulic cylinders should be inspected for external leakage and determine if the cab can be raised or lowered.
Check for internal leakage by observing bleed down. Make sure the mechanical stops engage and hold safely.
For what must you check the accelerator linkage?
Check the accelerator linkage for binding and lubricate it at appropriate locations.
For what should you test the brake pedal?
Test the brake pedal for operation and lubrication.
For what must you check the clutch-pedal?
Check the clutch-pedal Freeplay and if an adjustment is performed the work must be noted using a signoff or work performed sheet before the vehicle can be put back in service.\
If the problem did not require repair, but was still looked at, it should be noted as well.
What is a common problem with the electronic accelerator?
Dirt buildup around the throttle position sensor(TPS)
What is TPS?
The TPS is the variable resistor that supplies the ECM with throttle position information so the ECM can regulate engine performance and is located in the electronic foot pedal assembly (EFPA).
What do many systems use a 5-volt reference voltage for?
A 5-volt reference is sent from the ECM to the TPS, and the TPS returns a portion of it, proportional to pedal mechanical travel. The actual voltage signal returned to the ECM is converted to counts, which can be read with an EST.
How do you check the cab air suspension?
To check the cab air suspension, make sure that the air brake system pressure gauge reads the specified system cut-out pressure.
How do you check the cab ride height?
By using a tape measure at the location specified by the manufacturer. This is usually between the upper and lower plates.
Compare your readings with specifications and adjust the leveling valve as necessary.
Use a soap and water solution to check for leaks.
How do you check the condition of the shock absorbers in the cab suspension system?
Look for fluid leaks and observe any roughness in the ride when the cab is at normal ride height.
What do you look for in checking the condition of the transverse rod and mounts?
Look for excess lateral movement.
What should you do to inspect the front bumper, fairings, and mounts?
Check the front bumper to make sure that it is securely minted and is not cracked or damaged
Make sure there is sufficient space between the end of the bumper and the front tires to avoid damage to the tire.
The fairings should also be checked for cracks and that the mounts are tight and not damaged.
Why must the technician/inspector report and log all refrigerant leaks into a PMI schedule?
So these repairs are addressed in a timely manner.
Should all technicians who perform service on an A/C system of a motor vehicle be certified?
Yes, they must be certified, regardless of the capacity of the person: shop foreman, parts specialist, and technician.
Where is the condenser normally mounted?
The condenser is normally mounted just in front of the truck radiator, or if rooftop-mounted, in the center of the roof above the driver/passenger area.
How can you tell if there is a refrigerant leak?
Refrigerants carry oil with them and when they leak, there is usually an oily film around the source of the leak.
What instruments can you use to detect leaks in the A/C condenser?
Sometimes a dye has been added to the system to help locate leaks. These dyes are designed to be seen using a black-light leak detector.
Smaller leaks may require h use of electronic leak detectors.
What happens if a condenser is allowed to move or is subject to vibration?
May lead to more serious leaks.
What is the Clean Air Act?
The Clean Air Act establishes regulations concerning the repair of leaks. The technician/inspector must report and lo all refrigerant leaks into a PMI schedule so these repairs are addressed in a timely manner.
What is a preliminary inspection to check the condition of the A/C system and operation?
Check the compressor drive belt condition and tension.
Look at the compressor mountings, checking for loose bolts or cracked mounts.
Use a thickness gauge to check the compressor clutch condition.
Visually check for damaged or leaking hoses and road debris buildup on the condenser coil fins. If they are clogged with debris using compressed air, soapy water, a small brush, and a fin comb to clean the fins and restore airflow.
How can you find indications of mechanical pressure or charge level problems?
Engage the compressor with the engine idling and listen for indications.
What are some R-12 systems equipped with to check system charge?
Some R-12 systems are equipped with a sight glass that may be used to check system charge but R-134a systems are not.
Following the OEM-recommended procedure for troubleshooting the system, what does frost on the receiver/dryer usually indicate?
An internal restriction in that component.
The receiver/dryer is located in the high-pressure liquid line between the condenser and the evaporator, it should feel warm.
Following the OEM-recommended procedure for troubleshooting the system, what does thermal expansion valve (TXT) indicate?
A restricted valve or one sticking closed.
Following the OEM-recommended procedure for troubleshooting the system, what does frost formation on the evaporator outlet indicate?
A flooded evaporator, caused by an excessive refrigerant charge, or a stuck-open TXV.
Following the OEM-recommended procedure for troubleshooting the system, what do unusual noises often guide the technician to?
To a faulty component. These problems may also cause frost on the compressor suction line.
If a system uses an accumulator, how should it feel?
It should feel cold because of its close proximity to the evaporator. Both evaporator, inlet, and outlet should feel cold when operating normally.
If a system uses orifice tube systems, how should it feel?
The evaporator inlet should be slightly warmer to the touch than the outlet. If the evaporator outlet is warm, the refrigerant charge may be low.
How should High-side refrigerant components feel?
They should feel hot or warm, and low-side components should feel cool or cold.
What may a plugged drain in the evaporator cause?
May cause a sulfurous odor in the cab. R-12 has no odor, while R-134a has a faint ether-like smell.
How often should you change HVAC air inlet filters?
At least once a year, preferably at the beginning of summer.
What will a clogged evaporator core drain cause?
A clogged evaporator core drain will cause windshield fogging or a noticeable mist from the panel vents. A clogged drain normally can b opened with a slender piece of wire or with ow pressure shop air.
What noise will a cracked evaporator case cause?
A whistling noise during high blower operation. Minor cracks can be repaired using epoxy-type adhesives.
How can you fix a noticeable mildew smell during A/C operation?
Remove the evaporator case and washing it with a vinegar and water solution or a commercially available cleaner.
What does APUs (auxiliary power units) do?
APUs provide electrical power, cooling, and/or heating for the truck without operating the truck’s engine.
What do engine based systems need?
Engine based systems need oil, filters, and possibly drive belts at recommended maintenance intervals.
The fuel system, coolant hoses/clamps, belt tension, exhaust, mounting brackets, etc, need to be performed at regular intervals as well.
