Glossary of terms


Vehicle Technology Terms

Blind spot detection system (side vision aid):
Side vision aid alerts the driver if another vehicle is in the blind spot when changing lanes. When the signal, an indicator, typically located on the side-view mirror, signals whether a vehicle is in the blind spot.

Electronic Control Module (ECM):
The computer in an electronic control system, also known as an electronic control unit (ECU).

Electronic Power Steering (EPS):
EPS is a power steering system that varies the amount of steering assist according to engine or road speed. At slow speeds more steering assist is delivered and steering the wheels is easier; necessary for parking, etc. At higher speeds, steering assist is reduced and more steering effort is required to steer the car, giving the driver greater feel of the road. Electronic Stability Control

Electronic Stability Control has ABS's hardware and two additional sensors: SAS, which measures the position and rate the steering wheel is turning, and a yaw sensor, which measures the rate the vehicle is actually turning. By comparing them, the on-board computer will know if the vehicle is oversteering or understeering.

Lane Departure system:
Issues a warning when the vehicle edges off course and reaches the highway lane markers. It delivers a noticeable sound when the vehicle starts to move into an adjacent lane, whether due to inattention, drowsiness or distraction.

On-Board Diagnostics (OBD):
A diagnostic software system in the ECM or PCM that monitors computer inputs, outputs, and resultant engine/transmission operations for failure. OBD-ll has been a federally mandated system since 1996.

Powertrain Control Module (PCM):
On vehicles with computer control systems, the main computer that determines engine operation based on sensor inputs and by using its actuator outputs. The PCM may also control transmission operation.

Scan tool:
Device designed to communicate with a vehicle's on-board computer system to perform diagnostic and troubleshooting functions.

Steering Angle Sensor (SAS):
Determines the absolute angle position of a steering wheel of a motor vehicle.

Technical Service Bulletin (TSB):
Information published by vehicle manufacturers that describe updated service procedures and service procedures that should be used to handle vehicle issues.

Traction control system:
Traction control is designed to prevent a vehicle’s wheels from spinning on slippery surfaces. Each wheel "searches" for optimum traction several times a second and adjustments are made accordingly.

Vehicle Speed Sensor (VSS):
A permanent magnet sensor, usually located on the transmission, that provides an input to the vehicle computer control system regarding vehicle speed.

Wheel speed sensor:
A permanent magnetic sensor that sends information to the vehicle computer regarding wheel speed.

Yaw angle:
The angle of rotation of a body about a vertical axis with respect to the flow stream direction.


Alignment Terms

The process of measuring and positioning all wheels attached to a common chassis.

The inward or outward tilt of the top of the wheel as viewed from the front.

Camber roll:
The changes of camber that occur in a turn due to caster.

The forward or rearward tilt of the steering axis as viewed from the side.

Centerline steering:
A centered steering wheel with the vehicle tracking a "straight-ahead" course.

Directional stability:
The tendency for a vehicle to maintain a directed path.

The appearance given when the thrustline is not parallel with the centerline of the vehicle.

Drift (lead):
The tendency of a vehicle to steer away from a directed course. Less severe than a pull, constant pressure at the steering wheel is not needed to maintain straight-ahead.

Geometric centerline:
A line drawn through the midpoint of both front wheels and both rear wheels.

Independent suspension:
A suspension which provides an isolated mounting for left and right front wheels or left and right rear wheels.

Individual toe:
The angle formed by the intersection of an individual line drawn through the plane of one wheel and the centerline.

Non-independent suspension:
A suspension design which creates a direct connection between the left and right front wheels or left and right rear wheels.

The tendency of a vehicle to steer away from a directed course. A constant pressure is maintained by the driver at the steering wheel to travel straight ahead.

Thrust angle:
The angle formed between the thrustline and the geometric centerline.

The bisector of rear toe, also described as a line drawn in the direction the rear wheels are pointed.

Total toe (angular):
The angle formed by the intersection of lines drawn through both wheels of a given axle.

Total toe (linear):
The difference in measurements taken across the front of the tires versus a measurement taken across the rear of the same tires.

The interrelated paths taken by the front and rear wheels.

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