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You must comprehend how all the controls and equipment in any vehicle you drive as a professional work. Commercial automobiles differ significantly from household vehicles. Commercial vehicles contain a variety of systems, controls, and tools that are often absent from personal vehicles.


You should never drive a vehicle unless you are comfortable with its controls and instruments for safety reasons.


Engine Controls


The vehicle's engine is started and stopped using the engine controls. Despite being comparable in most vehicles, they do differ somewhat depending on the engine's manufacturer and type.


Engine control switch — The engine is started using the engine control switch. The engine cannot be started until it is turned on.


Starter button — There is a starting button on certain vehicles. You must first turn the engine key to the "on" position before pressing the starting button if the truck you are driving has one. About 3 to 5 seconds should be the typical cranking time.


Cruise control — Without touching the pedal, the vehicle may maintain a constant, steady pace thanks to cruise control.


Primary Vehicle Controls


Steering wheel — The vehicle is driven by turning the steering wheel. Its diameter is greater than that of your vehicle's steering wheel.


Accelerator pedal — The vehicle's speed is controlled via the accelerator pedal. Both a truck and an automobile, it is operated in the same manner. This may also be referred to as the throttle throughout your training. To increase speed, depress the throttle; to decrease speed, release it. By using the throttle properly, you may safely manage the vehicle's speed and prevent the need to often use the service brakes.


Clutch pedal — Shifting gears and engaging and disengaging the clutch are both done using the clutch pedal. There are four clutch locations.


  1. Engaged — The clutch is engaged when the pedal is completely released (i.e., your foot is not depressing the pedal). If the vehicle is in gear, the drive train and engine are linked.


  1. Free play — The amount of movement achievable with the clutch neither engaged nor disengaged is known as free play. To avoid excessive clutch wear, free play is essential. One to two inches is the typical free play.

  2. Disengaged — When the pedal is pushed between three and eight inches, the clutch disengages. The engine and drive train are divided at this position. To start the engine or change gears, the clutch must be released.


  1. Clutch brake — A large truck's gearbox "free-wheels" or spins while it is not engaged. To engage the next gear, you must utilize the clutch brake to stop the gearbox from rotating. The clutch brake will activate when the clutch pedal is pressed to the floor, stopping the gearbox and allowing the driver to choose the proper starting gear (forward or reverse).


If the clutch pedal is not utilized correctly, serious harm may be done to the gearbox or drive system.


Transmission controls — Depending on the truck's gearbox type, there are several transmission controls.


A clutch and a gear shift lever are used in a manual gearbox. You have to shift gears manually.


The range selection lever on the gear shift lever may let you alternate between the high and low ranges. The low range of gears is included in the down position, while the high range of gears is included in the up position. On 13 and 18-speed gearboxes, you may divide gears using a splitter valve or button.


A clutch and gear shift lever are features of a semi-automatic gearbox. A control pad with push buttons might be used in place of the gear change lever. An onboard computer can change gears for you, but you can also do it manually.


Only a touchpad or lever is used to change gears with an automatic gearbox. Some models may not need a clutch. Hydraulics and an onboard computer control all gear changes.


Brake controls (air brakes) — The vehicle may be slowed down or stopped using the brakes. The air brake control system is complex and has several independent controls.


  1. Foot brake control valve — The foot brake control valve, also known as the service brake, foot valve, the treadle valve, is used to activate the service brakes on both the tractor and the trailer. It provides air pressure to all brake chambers when depressed.
  2. Trailer brake hand-control valve — Only the service brakes on the trailer are controlled by the trailer brake control valve, also known as the hand valve, trolley valve, or independent trailer brake. It is only used in unique circumstances. It should not be used to slow down the vehicle or keep equipment in place when it is parked. The trailer might slide or jack-knife if it is used incorrectly.
  3. Parking brake control valve — The driver may engage the parking brake by turning a yellow, four-sided, diamond-shaped knob on the parking brake control valve. Only activate the parking brake when the vehicle is stopped. Before getting out of the driver's seat or shutting off the engine, the parking brake should always be applied. Even if it is thought that the vehicle is on level ground, failure to engage (set) the parking brake might cause the vehicle to roll.
  4. Trailer air supply valve — The trailer air supply valve, the red eight-sided button, controls air supply to trailer brakes. It must be released (pushed in) for normal operation with a trailer and applied


Antilock brakes — All truck tractors produced on or after March 1, 1998, must be fitted with an antilock braking system (ABS) by National Highway Traffic Safety Administration (NHTSA) regulations (49 CFR 571 S5.1.6.1). Antilock brakes, when utilized correctly, aid in preventing wheels from locking or losing traction, which may result in a loss of vehicle control.


How you use the brakes to stop the vehicle is where ABS and other braking systems diverge most. Normally, while using conventional brakes, you would press the brake pedal. For the brakes to function correctly with ABS, the pedal must be pressed firmly and continuously.


Auxiliary brakes and retarders — These devices slow down the vehicle without using the service brakes. They prevent misuse and overheating of the service brakes. Only dry road surfaces need to be utilized with them. The four fundamental categories of auxiliary brakes and retarders.


  1. Exhaust brakes — Considered to be the most basic kind of heavy vehicle retarder, exhaust brakes. The exhaust manifold has a valve placed to prevent exhaust gas egress. As a result, the engine experiences back pressure, which keeps it from speeding up. An on/off switch in the cab or an automated control switch on the accelerator or clutch is often used to operate exhaust brakes.


  1. Engine brakes — Engine brakes, which adjust valve timing and convert the engine into an air compressor, are incorporated inside the engine head. When you take your foot off the clutch and accelerator, a switch situated on the dashboard activates them.


  1. Hydraulic retarders — HDriveline retarders include hydraulic retarders. Typically, they are positioned between the engine and the flywheel. They do this by directing the flow of oil. They reduce a against the stator vanes, which slows down the vehicle. They might be turned on using an accelerator switch or a hand lever.


  1. Electric retarders — Electric retarders have electromagnets inside of them that slow the connected rotors to the motor train. In the cab, there is a switch that controls them.


The four different auxiliary braking system types are uncommon in trucks. Trucks often only have one. Each driver must be aware of the sort of vehicle they are operating and how it functions.


Interaxle differential lock — The rear tandem axles are locked and unlocked via an interaxle differential lock. The axles may turn independently of one another on a dry surface when they are in the unlocked position. Power to the axles is balanced in the locked position to stop traction-deficient wheels from spinning. Never use interaxle differential locking for any longer than required.


Secondary Vehicle Controls


Your vehicle's secondary controls help you drive it safely. Some are comparable to your vehicle's secondary controls. Some are specific to trucks. Although the quantity and kind of controls vary from vehicle to vehicle, they normally fit into one of the four categories listed below.


  • Seeing:

  • Lights

  • Windshield wipers and washers

  • Remote mirrors

  • Mirror heaters

  • Defroster

  • Communication:

  • Horns

  • Lighting, including turn signals, four-way flashers, high beams, and fog lights; brake lights, etc.)

  • CB Radio (not a vehicle control but is used in communication)

  • Comfort/Climate controls:

  • Heater

  • Air vents

  • Seat position and adjustment control

  • Air conditioner

  • Driver safety:

  • Bunk restraints

  • Seat belts

  • Door locks


Before you go on the road, you should be comfortable with and knowledgeable about any secondary controls on your vehicle.


Vehicle Instruments


Vehicle instruments track and report on your vehicle's operational status. They forewarn you of possible issues. Below is a list of fundamental instruments.


    • Speedometer — Sec. 393.82 of the Federal Motor Vehicle Safety Regulations mandates the use of a speedometer (FMCSRs). The vehicle's speed is shown on the speedometer in kilometers per hour (kph) or miles per hour (mph).

    • Odometer — The odometer shows how many miles (or kilometers) a vehicle has driven overall.

    • Tachometer — The engine speed is shown on the tachometer in hundreds of revolutions per minute (RPM). It acts as a reference point for selecting the proper transmission gear. Additionally, it helps you use the engine and gearbox efficiently for both fuel economy and acceleration and deceleration.

    • Fuel gauge — The fuel gauge displays the amount of petrol remaining in the vehicle's fuel tank(s). Before you go on a journey, visually inspect the gasoline tank(s) since fuel gauges are not always reliable.

    • Ammeter — The amount of battery being charged or drained is measured by the ammeter. A reading that is slightly off is considered abnormal. Constantly high charges or discharges are warning indications of issues. Not all commercial vehicles have ammeters. For charging-related concerns, consult a voltmeter if your vehicle lacks one.

    • Voltmeter — The voltmeter uses volts to measure battery output. To get a typical reading for the vehicle you are running, you should consult the owner's handbook. A typical measurement in the majority of automobiles is between 13 and 14.5 volts. A battery's lifespan might be shortened by higher or lower than normal voltage.

    • Air pressure gauge — The reservoir's or tanks' air pressure is measured in pounds per square inch via the air pressure gauge (psi). There might be one or two air pressure gauges on a vehicle. The primary and secondary air pressure gauges are the names of these gauges. Every commercial motor vehicle with air brakes must have an air pressure gauge, as required by law. Air pressure begins to increase as quickly as the engine starts. It keeps increasing until the highest pressure is attained (about 120 psi). A low-pressure warning system (light or buzzer) will turn on if the pressure falls below 60 psi, signaling that it is hazardous to continue operating the vehicle. The tractor protection valve shuts between 20 and 45 psi, cutting off the air supply to the trailer. You should not drive a vehicle with insufficient air pressure.

    • Oil pressure gauge —You can check whether the engine is adequately maintained by looking at the oil pressure indicator. After the car is started in warm conditions, the oil pressure should begin to show on the oil pressure indicator and gradually increase to the usual operating range. A 30 to 50 PSI working range is typical. It could take 30 to 60 seconds to acquire a reading when it's freezing outside. The normal range varies depending on the engine speed and oil viscosity of each vehicle. The engine is not properly lubricated if the pressure is low or doesn't register. This can cause the engine to be ruined within a short time period. You should know the operating range of your vehicle and stop and investigate anytime there’s a loss in pressure or pressure doesn’t register.

    • Coolant temperature gauge — The engine block's water and coolant temperatures are measured via the coolant temperature gauge. The engine is shielded from heat-related damage by the cooling system. An engine typically runs between 170° and 195°F. This may change. For details, refer to the vehicle's owner's handbook. The engine may be overheating if the gauge reads over the usual range you should stop the engine sight away.

    • A gauge for oil temperature. Engine oil temperature is shown on the engine oil temperature gauge. Between 180° and 225°F is the typical engine oil temperature. This may change. For details, refer to the vehicle's owner's handbook. Oil may become thinner at a high temperature, which lowers oil pressure. This can harm the engine.

    • Exhaust pyrometer gauge — The exhaust pyrometer gauge displays the manifold's exhaust gasses' temperature. However, most vehicles will have cooled down sufficiently by the time you arrive at the fuel stop or dock due to a natural drop in workload (lowering speed going off the highway) and a constant flow of air through the engine. This is true even if the truck does not have an exhaust pyrometer.

      • Axle temperature gauge — The temperature of the front and rear drive axles is measured by the axle temperature gauge. Readings over normal may be a sign of poor bearings.

      • Warning devices — There are other warning systems in vehicles. They alert you when temperatures or pressures are at dangerous levels. The following is a list of some of the most popular warning devices.


  • Low pressure warning alarm/light — The air brake system's insufficient pressure is indicated by the low-pressure warning alert or light.

  • Coolant level alarm — The coolant level alarm lights up when the level starts dropping, indicating a prob- able leak.

  • Oil level alarm — When the oil level falls below what is required for functioning, the oil level warning turns on.

  • Coolant temperature warning light — When the temperature is too high for regular functioning, the coolant temperature warning light lets you know.

  • Oil pressure warning light — When the oil pressure becomes too low for safe operation, the oil pressure warning light flashes.

  • Pyrometer warning light — The pyrometer warning light lets you know when the exhaust temperatures are out of the ordinary.

  • Differential warning — When the interaxle differential is locked, the differential warning could continue to glow.

  • ABS light — This light indicates a malfunction with the ABS function.


Every truck driver has to be informed of what these warning indicators in their vehicle imply and what can happen if they are not immediately heeded. When one of these signs illuminates when a fault is discovered, certain trucks will quickly cut off the engine. Others will lower the engine's speed to give the driver more time to swiftly and safely remove the vehicle off the road. In any event, the motorist has to be aware of what they signify and what to do if an alarm, buzzer, or indication light goes off while they are driving.




You learned about vehicle controls and instruments in this chapter. Before driving a vehicle, you should make sure you are comfortable with these components as a professional driver. While driving, it is also important to regularly inspect the instrument panel. Your ongoing scanning motion, which we shall talk about later, should include this. The driver may stay aware of any changing truck conditions and respond appropriately to possibly prevent damage or breakdown by continuously monitoring these systems.

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