Noise is any undesirable sound, usually unpleasant in nature. Vibration is any motion, shaking or trembling, that can be felt or seen when an object moves back and forth or up and down. Harshness is a ride quality issue where the vehicle's response to the road transmits sharply to the customer. Harshness normally describes a firmer than usual response from the suspension system. NVH is a term used to describe these conditions, which result in varying degrees of dissatisfaction. Although a certain level of NVH caused by road and environmental conditions is normal, this section is designed to aid in the diagnosis, testing and repair of NVH symptoms.
Acceptable NVH
All internal combustion engines and drivelines produce some noise and vibration; operating in a real world environment adds noise that is not subject to control. Vibration isolators, mufflers and dampers reduce these to acceptable levels. A driver who is unfamiliar with a vehicle can think that some sounds are abnormal when actually the sounds are normal for the vehicle type. As a technician, it is very important to be familiar with vehicle features and know how they relate to NVH symptoms and their diagnosis. For example, if the vehicle has automatic overdrive, it is important to test drive the vehicle both in and out of overdrive mode.
Glossary of Terms
Amplitude
The quantity or amount of energy produced by a vibrating component (G-force). An extreme vibration has a high amplitude. A mild vibration has a low amplitude. See Intensity.
Boom
Low frequency or low pitched noise often accompanied by a vibration. Also refer to Drumming.
Buffet/Buffeting
Strong noise fluctuations caused by gusting winds. An example would be wind gusts against the side glass.
Buzz
A low-pitched sound like that from a bee. Often a metallic or hard plastic humming sound. Also describes a high-frequency vibration. Vibration feels similar to an electric razor.
Chatter
A pronounced series of rapidly repeating rattling or clicking sounds.
Chirp
A short-duration, high-pitched noise associated with a slipping drive belt.
Chuckle
A repetitious, low-pitched sound. A loud chuckle is usually described as a knock.
Click
A sharp, brief, non-resonant sound, similar to actuating a ball point pen.
Clonk
A hydraulic knocking sound. Sound occurs with air pockets in a hydraulic system. Also described as hammering.
Clunk/Driveline Clunk
A heavy or dull, short-duration, low-frequency sound. Occurs mostly on a vehicle that is accelerating or decelerating abruptly. Also described as a thunk.
Conductor
The components that carry (transmit) a vibration frequency from the originator to the reactor.
Cycles Per Second
Cycles per second. Same as hertz (Hz).
Cracks
A mid-frequency sound, related to squeak. Sound varies with temperature conditions.
Creak
A metallic squeak.
Cycle
The process of a vibrating component going through a complete range of motion and returning to the starting point.
Decibel (dB)
A unit of measurement, referring to sound pressure level, abbreviated dB.
Drone
A low-frequency, steady sound, like a freezer compressor. Also described as a moan.
Drumming
A cycling, low-frequency, rhythmic noise often accompanied by a sensation of pressure on the ear drums. Also described as a low rumble, boom or rolling thunder.
Flutter
Mid to high intermittent sound due to air flow. Similar to a flag flapping in the wind.
Frequency
The rate at which a cycle occurs within a given time.
G-force
The additional load or weight produced in an object during acceleration. When measuring the level or amplitude of a vibration without sound, the unit G is added to associate the force of the vibration to gravity. This is similar to measuring the weight of an object, which is also a function of gravity.
Gravelly Feel
A grinding or growl in a component, similar to the feel experienced when driving on gravel.
Grind
An abrasive sound, similar to using a grinding wheel, or rubbing sand paper against wood.
Hertz (Hz)
A unit of measure used to describe noise and vibration concerns expressed in cycles per second.
Hiss
Steady, high-frequency noise. Vacuum leak sound.
Hoot
A steady, low-frequency tone, sounds like blowing over a long neck bottle.
Howl
A mid-range frequency noise between drumming and whine. Also described as a hum.
Hum
Mid-frequency steady sound, like a small fan motor. Also described as a howl.
Intensity
The physical quality of sound that relates to the strength of the vibration (measured in decibels). The higher the sound's amplitude, the higher the intensity and vice versa. See Amplitude.
Knock
A heavy, loud, repetitious sound, like a knock on the door.
Moan
A constant, low-frequency tone. Also described as a hum.
Ping
A short-duration, high-frequency sound, which has a slight echo.
Pitch
The physical quality of sound that relates to its frequency. Pitch increases as frequency increases and vice versa.
Pumping Feel
A slow, pulsing movement.
Rattle
A random and momentary or short-duration noise.
Reactor
The component, or part, that receives a vibration from an originator and conductor and reacts to the vibration by moving.
Roughness
A medium-frequency vibration. A slightly higher frequency than a shake. This type of vibration is usually related to drivetrain components.
Rustling
Intermittent sound of varying frequency, sounds similar to shuffling through leaves.
Shake
A low-frequency vibration, usually with visible component movement. Usually relates to tires, wheels, brake drums or brake discs if it is vehicle speed sensitive, or engine if it is engine speed sensitive. Also referred to as a shimmy or wobble.
Shimmy
An abnormal vibration or wobbling, felt as a side-to-side motion of the steering wheel in the driveshaft rotation. Also described as waddle.
Shudder
A low-frequency vibration that is felt through the steering wheel or seat during light brake application.
Slap
A resonance from flat surfaces, such as safety belt webbing or door trim panels.
Squeak
A high-pitched transient sound, similar to rubbing fingers against a clean window.
Squeal
A long-duration, high-pitched noise.
Tap
A light, rhythmic or intermittent hammering sound, similar to tapping a pencil on a table edge.
Thump
A dull beat caused by 2 items striking together.
Tick
A rhythmic tap, similar to a clock noise.
Tip-In Moan
A light moaning noise heard during light vehicle acceleration, usually between 40-100 km/h (25-65 mph).
Transient
A noise or vibration that is momentary, a short duration.
Vibration
Any motion, shaking or trembling, that can be felt or seen when an object moves back and forth or up and down.
Whine
A constant, high-pitched noise. Also described as a screech.
Whistle
High-pitched noise with a very narrow frequency band. Examples of whistle noises are a turbocharger or air flow around an antenna.
Wind Noise
Any noise caused by air movement in, out or around the vehicle.
Noise, Vibration and Harshness (NVH) - Diagnosis and Testing
Special Tool(s) Diagnostic Theory The shortest route to an accurate diagnosis results from: system knowledge, including comparison with a known good system. system history, including repair histo ...Other materials:
Steering System
DESCRIPTION AND OPERATION
Steering System
Electronic Power Assist Steering (EPAS) System
The Electronic Power Assist Steering (EPAS) system consists of the following
components:
Power Steering Control Module (PSCM) - the PSCM controls the functions
of the EPAS system and com ...
Changing the wiper blades
1. Pull the wiper blade and arm away
from the glass.
2. Squeeze the locking tabs to release
the blade from the arm and pull the
blade away from the arm to remove it.
3. Attach the new blade to the arm
and snap it into place.
Replace wiper blades at least once per
year for optimum per ...
Tire care
Information About Uniform Tire Quality Grading
Tire Quality Grades apply to new
pneumatic passenger car tires. The Tire
Quality Grades can be found where
applicable on the tire sidewall between
tread shoulder and maximum section
width. For example:
• Treadwear 200 Traction AA Temperature ...