An instrument used to indicate to the driver how quickly an engine is rotating in its current gear. Measured in Revolutions Per Minute, the indicator also frequently includes the maximum engine speed as a redline on the meter to denote the highest achievable RPMs.

Tail Lights

Light housings on the rear end of a vehicle which are used to add more visibility during its operation. Light fixtures include brake lamps which activate while the brake pedal is depressed, reverse lights while a vehicle is moving backwards, and rear turn signals which indicate to following motorists which direction a vehicle is turning or merging.


A type of convertible sports car or other vehicle with either a panel or hood which can be removed. In most cases, a central roll bar remains behind the seats to maintain passenger safety.


Refer to “Traction Control System” for more information.

Technical Service Bulletin

Also known as “TSBs,” notices issued by a manufacturer describing problems which may be impacting the normal operation or performance of a vehicle. In some cases these bulletins are denoted as “Secret Warranties” as they cover known problems in vehicle models. They also provide explicit instructions to service technicians on how to properly repair the identified issue. The bulletins are primarily distributed to all manufacturer dealerships for consistent repair instructions. Car owners can have these repairs completed free of charge if they have them completed within a warranty period as long as the service technician is able to identify and replicate the described problem. TSBs are different from recalls as they only cover problems which impact vehicle performance. Recalls also cover repairs for safety-related issues or emissions problems. Furthermore, recalls are completed with a no-questions-asked policy whereas TSB repairs are only completed when they can be identified and confirmed by manufacturer service technicians. While these bulletins are typically only sent to service centers, owners may also receive a notice depending on the issue. Owners can also search online to determine if their vehicles have any current TSBs.


An integrated telecommunications system equipped in a vehicle – usually including Bluetooth integration.


The combined usage of both a telecommunications system and electronic data communication equipped in a vehicle. The precise specifications of these systems will vary based on vehicle models.

Thermostatically Controlled Air Cleaner

Also known as a “Heated Air Inlet,” a device which is present in carburetor engines for emissions control. A thermostat-controlled diverter is equipped which moves warm air from the exhaust manifold directly into the carburetor in colder environmental conditions. Once a minimum temperature has been reached, ambient air can then be moved into the carburetor in the same fashion. This process is used to warm up the engine operations at a much faster speed than just an ambient air system by reusing air which has already increased its temperature from engine operations. It can quickly reduce the fuel-rich and inefficient cold temperature operation to more efficiently utilize fuel during combustion.

Throttle and Kick Down Lever Ball Studs

Lubricated pivot points used for either the throttle or the kick down linkages. These points allow the necessary motion with these essential engine components. Properly lubricated studs ensure ideal performance of a vehicle.

Throttle Linkage

The combined set of all the mechanical connections occurring between a vehicle’s throttle body or carburetor and its accelerator pedal. All linkage components must remain in good repair for ideal throttle operation. Malfunctioning or degraded linkage could significantly alter both throttle and overall engine performance.

Throttle System

All the components which are used within the throttle to control the precise volume of air entering into an engine system.

Tire Rod Ends

Socket and ball parts of a steering linkage system which are used to connect the rack and pinion or center link to the wheel spindles. These components connect between the steering wheel and axles to translate accurate movement.

Tier 1 EPA Program

The inaugural vehicle emissions program first implemented under the U.S. Clean Air Act of 1994 to set higher standards for the release of damaging pollutants into the atmosphere. This first program began to shift the focus on responsible production of vehicles in terms of their harmful chemical substances during operation. Since the first program, multiple other initiatives and standards have been released, and they have led to further pushes for cleaner and greener vehicles.

Tier 2 EPA Program

The second vehicle emissions program released by the EPA increasing the standards beyond Tier 1 for cleaner emissions from combustion engines. This program comes in direct response to the 1994 Clean Air Act. The standards at this tier have elevated the push toward cleaner, more environmentally responsible emissions. Over time, cleaner emissions have become a selling point for vehicles, motivating manufacturers to continue pushing innovations to improve combustion efficiency and reduce pollution even more.

Timing Belt

A “toothed” style belt which is used to drive over an overhead camshaft or series of camshafts to maintain proper timing of all the mechanisms in the system. In some vehicles, these belts are also equipped on a vehicle’s Water Pump.

Timing Belt Tensioner

A device which adds tension to a vehicle’s Timing Belt using an idler wheel that is spring loaded to apply force. It keeps the Timing Belt operating at a stable and synchronized level which effectively prevents the camshaft controls from becoming desynchronized as well. Synchronicity in these components ensures smooth operation and optimal performance of all vehicle systems.


A light reducing, transparent plastic film which is applied directly to a vehicle’s windows. Some tinted windows are used to amplify privacy within a vehicle. They can also reduce visible light, lower heat transmission between the glass and the cabin, and reduce UV or infrared light transmission which comes from direct sunlight.

Tire Diameter

The total measurement of a tire’s diameter, typically measured in inches. Depending on the model, a vehicle may accommodate up to a specific diameter tire and wheel to ride safely.

Tire Inflator

A reusable device or disposable product which can inflate a flat or spare tire and restore safe pressure. Some inflation devices can also inflate and introduce a sealant for smaller leaks or punctures.

Tire Inflator Sealant Cartridge

A disposable cartridge which contains a pressurized compound designed to seal tires from leaks or punctures.

Tire Load Index

Otherwise known as a “Load Rating,” this numerical value indicates a tire’s total capability to safely carry a payload. Tire ratings are determined by the manufacturer, and higher index measurements indicate a greater overall load capacity while maintaining safe functionality. Tires with higher Load Index values are often used for heavy-duty operations or on larger, heavier vehicles which may carry more weight. A mismatched Tire Load Index may damage tires or cause unsafe operating condition.

Tire Prefix

An alphabetic code value designated to tires by their manufacturers which indicates its appropriate usage. For example, a “P” Tire Prefix means that a tire is suitable for passenger cars. An “LT” designation is used to denote light trucks for lightweight payloads. Improper tires may cause damage or affect the safe operation of a vehicle.

Tire Pressure Monitoring System

An electronic system equipped within a vehicle which continually monitors a vehicle’s tire pressure and reports the numbers to the driver. Recommended tire pressure levels are supplied by either the tire or vehicle manufacturer. The system ensures that tire pressures remain at safe levels.

Tire Profile

A numerical value which is assigned by the manufacturer for tire types and denotes the measurements between the tread width and its sidewall height from the rim to the tread. For example, a Tire Profile of 50 indicates that the sidewall height is 50% of its tread width.

Tire Size

Critical data points related to the exact measurement specifications for a tire. Printed onto a tire’s sidewall, this data includes its physical dimensions, Speed Rating, and total load capacity. In most cases, tires also list the Tire Prefix and Tire Profile ratio.

Tire Speed Rating

An alphanumeric value placed on a tire which indicates the maximum speed it can safely operate without failure over a ten minute period. These ratings are determined by manufacturers through a series of stress and durability tests. Higher-grade ratings are often used for vehicles which regularly operate at faster speeds such as racing cars.


Also known as a “Pink Slip,” this legal document denotes the person or entity that holds legal ownership over a vehicle. Titles are issued within the state where the vehicle is sold. New owners must transfer title registration to reflect the change in ownership. This is an essential document to reflect the legal ownership of a vehicle. It is also required for multiple other vehicle-related activities and processes.


A measurement which denotes the engine’s power capability by showing how much force it can apply to rotate its crankshaft at a determined engine speed. Torque is one of the primary factors which determines the total “work” an engine is capable of doing.

Total Due at Signing

Refer to “Drive Off Fees” for more information.

Tow Hooks

Hooks or eyelets attached to a structurally strong area of a vehicle frame. Usually constructed out of a durable metal, these hooks serve as pickup points while using towing cables. They are usually recommended for use on stronger, larger, and more rugged vehicles as other vehicles may not be appropriate for towing. This includes pickup trucks, SUVs, and similar automobiles.

Towing Capable

A vehicle model equipped with features and devices used for safely and effectively pulling a trailer behind it. Devices include a Trailer Hitch, Trailer Wiring, and related components.

Towing Capacity

The maximum amount of payload a vehicle is able to safely tow behind it on a trailer. This manufacturer-determined weight limit helps prospective vehicle owners to better understand the limitations a vehicle may have for its towing ability.


Also known as the “Axle Track,” the measured distance from a wheel’s center plane to the opposing wheel’s center plane on the same axle. Two axle vehicles have further distinctions for “Front Track” and “Rear Track” as they may vary.

Traction Control

Sometimes referred to as a “Traction Control System,” or “TCS,” a vehicle safety feature which helps to regulate wheel spin and keep drivers in control while accelerating. The system regulates wheel spinning to maximize the traction levels and the contact of tires with the road. This stabilization occurs by automatically activating and adjusting multiple components of a vehicle’s engine and braking systems based on current traction conditions. This includes adjustment of brake pressure (on either one or more wheels), closing of the throttle to slow down acceleration, and reduction of the fuel supply within one or more of the engine cylinders. Automatic regulation of traction improves driver safety and helps to prevent dangerous slippage and accidents.

Traction Control System

Refer to “Traction Control” for more information.

Trade In

A buyer-owned automobile which is exchanged during the purchase of a new or used vehicle to lower the net price paid. The exact price paid in the exchange of a vehicle depends on the vehicle’s year, make, model, condition, mileage, and other dealer-determined criteria. Many dealerships offer trade incentives such as a minimum amount paid to attract prospective buyers and increase sales. The traded vehicle is transferred over to the dealer during the new or used automobile purchasing process.

Trailer Hitch

A durable, metal attachment connected to the back area of a vehicle’s frame or chassis which provides the connection point for attaching a trailer to a vehicle. Hitches are only equipped on vehicles strong enough to safely tow trailers. This includes larger automobiles such as pickup trucks, vans, and SUVs.

Trailer Hitch Mountings

The mounting points on a trailer hitch used to attach a trailer onto a vehicle’s body or other area of the chassis.

Trailer Wiring

A flat, four-way weatherproof connector which is located near the trailer hitch of equipped vehicles. The wiring is used to complete all the circuits for a towed trailer to provide power to its indicator components. This includes a ground, running lights, left and right turning signals, and brake lights. Trailers must be wired for these lights to allow legal towing.


The combination of a vehicle’s transmission system and its differential or drive axle in one fully integrated assembly.

Transfer Case

Component of a vehicle’s drivetrain within four wheel drive, all wheel drive, or other multi-axle powered automobiles. This device transfers the generated power from the transmission into both the front and rear axles using the drive shafts.

Transfer Case Fluid

Fluid which is used to provide lubrication within a vehicle’s Transfer Case. Refer to “Transfer Case” for more information.

Transmission Modes

Transmission settings which can be manually selected by a driver and used to change drive ratio or shifting points. Adjusting these settings can improve vehicle performance or boost fuel efficiency depending on the conditions.

Transmission Overdrive

The last gear in an automatic transmission system which yields an output speed greater than the input speed. This overdrive setting can also increase fuel efficiency in highway driving conditions by allowing the engine to run at a lower RPM and maintain cruising speed.

Transmission Type

The precise type of transmission system used within a vehicle’s engine. The primary options include a manual, automatic, shiftable automatic, and an automated manual transmission.

Trip Computer

A computerized system within a vehicle which displays critical trip information during operation. The system can calculate mileage and time, report total distance traveled, outline the average speed, and provide a measurement of the average fuel economy throughout the trip.


A style of vehicle roof containing removable panels placed between a rigid bar running from the middle of a vehicle’s A Pillar to the same spot on its B Pillar. Panels are usually comprised of metal or other material the same color as the rest of the outer body. When removed, the rigid bar forms a “T” shaped appearance.


Also known as a “Turbosupercharger,” this equipped device is used to force additional air into an internal combustion engine used to amplify the total amount of power being produced. An exhaust-driven turbine pushes the air back into the combustion chamber, and this increase in total pressure provides the extra power boost within an engine.

Turn Signals

Devices installed in all vehicles which flash amber colored lights used to indicate that a driver intends to either turn or make a lane change. Use of signals is a critical safety requirement to keep other drivers alerted of a vehicle’s intended direction.

Turning Circle

Commonly known as a vehicle’s “Turning Diameter,” a measurement of a vehicle’s circle diameter when the steering wheel is fully locked one direction for a 360 degree turn. The diameter helps to determine the total amount of clearance a vehicle needs within turning motions.

Two Stage Unlocking

Remote-controlled electronic door unlocking system which will unlock the driver’s side door when first activated and the rest of the doors on the second activation. The remotes are usually electronic fobs with or without a vehicle key. Many vehicles also turn on parking lights to indicate when the door has been unlocked.

Twelve Volt DC Outlet

More commonly denoted as “12V DC Outlet,” an electrical socket which receives a 12 volt DC current. It is generated, stored, and supplied by the vehicle’s internal charging system.