| Description and Operation Definitions Noise is any unwanted sound, usually unpleasant in nature. Possible sources of noise are: - the engine.
- the engine accessories.
- the intake and exhaust systems.
- the driveline.
- electric motors and pumps.
- the wind.
- mechanical pumps.
- the road surface.
Vibration is an unwanted periodic motion of a body or medium. It may be felt, heard, or seen. Possible sources of vibration include the: - tires.
- engine.
- engine accessories.
- suspension.
- driveline.
- exhaust system.
Harshness refers to the ride quality and is very subjective. Reference to the previous conditions is usually the only way to identify harshness as a symptom. Normal Noise, Vibration and Harshness All internal combustion engines and drivelines produce some noise and vibration; operating in a real world environment adds noise and vibration that are not subject to control. Vibration isolators, mufflers and dampers are used to reduce these to acceptable levels. A driver who is unfamiliar with a vehicle may 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 concerns and their diagnosis. If, for example, the vehicle has automatic overdrive, it is important to test drive in and out of overdrive mode. Diagnostic Theory The shortest route to an accurate diagnosis results from: - system knowledge, including comparison with a known good system.
- system history, including repair history and usage patterns.
- condition history, especially any relationship to repairs or sudden change.
- knowledge of probable causes.
- using a systematic diagnostic method that divides the system into related areas.
The diagnosis and correction of noise, vibration and harshness concerns requires: - a road test to determine the exact nature of the concern.
- an analysis of the possible causes.
- testing to verify the cause.
- repairing any concerns found.
- a road test to make sure the concern has been corrected or brought back to within a normal range.
Glossary of Terms Acceleration The act or process of increasing speed. Acceleration occurs at light, medium, or wide-open throttle (WOT) conditions. Light Acceleration An increase in speed at less than half throttle. Medium Acceleration An increase in speed at half to nearly full throttle. WOT Acceleration An increase in speed at wide-open throttle. Ambient Temperature The surrounding or prevailing temperature. Articulation The relative movement of attached components. Belt Chirp A high-pitched short-duration noise usually caused by belt misalignment. Belt Squeal A high-pitched long-duration noise usually caused by belt slippage. Boom A low-frequency (sometimes cycling) noise, often felt as well as heard. Bound Up A stressed isolation mount or component that transmits vibration instead of damping or isolating it. Brakes Applied The use of the brakes to keep the vehicle from moving. Camber The angle of the wheel in relation to the true vertical as measured looking from the front of the vehicle. Camber is positive when the wheel angle is offset so that the top of the wheel is positioned away from the vehicle. Caster The angle of the steering knuckle in relation to the true vertical as measured looking from the side of the vehicle. Clunk A short-duration, dull sound usually associated with the transaxle engaging in reverse or drive. Coast/Deceleration The vehicle is in motion and the transaxle is engaged, but no pressure is applied to the accelerator pedal. Speed control, if equipped, is disengaged. Coast/Neutral Coast The vehicle is in motion with the transaxle disengaged. CPS Cycles per second. Cruise Constant speed on level ground; neither accelerating nor decelerating. Deceleration Slowing of the vehicle by releasing the accelerator pedal, but without using the brakes. Drive Engine Run-Up Test The operation of the engine through the normal rpm range with the vehicle standing still and the transaxle engaged. This test is used for vibration checks. Drivetrain All power transmitting components from the engine to the wheels; includes the torque converter, the transaxle and the halfshafts. Dynamic Balance The equal distribution of weight on each side of the centerline, so that when the wheel and tire assembly spins there is no tendency for the assembly to move from side to side (wobble). Dynamically unbalanced wheel and tire assemblies can cause wheel shimmy. For additional information, refer to Section 204-04 Wheels and Tires. for the appropriate balancing procedures. Engine Imbalance An exaggerated engine movement or vibration that directly increases in frequency as the engine speed increases. Engine Shake A condition in which the engine vibrates excessively at idle. Engine Misfire When ignition in one or more cylinders does not occur or occurs at the wrong time. Float A drive mode on the dividing line between cruise and coast where the throttle setting matches the engine speed with the road speed. Gravelly Feel A grinding or growl in a component, similar to the feel experienced when driving on gravel. Harshness A firmer-than-usual response of a component. Hz Hertz; a frequency of one cycle per second. Imbalance Out of balance; heavier on one side than the other. In a rotating component, imbalance often causes vibration. Inboard Toward the vehicle centerline. Isolate To separate from the influence of other components. Neutral Engine Run-Up Test The operation of the engine through the normal rpm range with the vehicle standing still and the transaxle disengaged. This test is used to identify engine related vibrations. Neutralize/Normalize To relieve stress from possible bound-up components. NVH Noise, vibration and harshness. Outboard Away from the centerline of the vehicle. Pumping Feel A slow pulsing movement. Radial/Lateral Radial is in the plane of rotation; lateral is at 90 degrees to the plane of rotation. Road Test The operation of the vehicle under conditions intended to produce the concern under investigation. Runout Out of round or wobble. Shake Low frequency vibration, usually with visible movement. Static Balance The equal distribution of weight around the wheel. Statically unbalanced wheel and tire assemblies can cause a bouncing action called wheel tramp. This condition will eventually cause uneven tire wear. For additional information, refer to Section 204-04 Wheels and Tires. for the appropriate balancing procedures. Tip-In Moan A light moaning noise heard during light vehicle acceleration, usually between 40-100 km/h (25-65 mph). TIR Total indicated runout. Tire Deflection The change in tire diameter in the area where the tire contacts the ground. Tire Force Vibration A tire vibration caused by variations in the construction of the tire that is noticeable when the tire rotates against the pavement. This condition may be present on perfectly round tires because of variations in the inner tire construction. Tire Flat Spots A condition commonly caused by letting the vehicle stand when the tires are warm. It can be corrected by driving the vehicle until the tires are warm. This concern is more likely to occur with N, V and Z-speed rated tires. Tire wear caused by wheel-locked skids. Two-Plane Balance Radial and lateral balance. Vibration An unwanted periodic motion of a body or medium. It can be felt, heard or seen. | 
