Road Test Quick Checks

1. 24-80 kph (15-50 mph): With light acceleration, a moaning noise is heard, and possibly a vibration is felt in the floorpan. It is usually worse at a particular engine speed and at a particular throttle setting. It may also produce a moaning sound. Refer to Pinpoint Test A. A: Tip-In Moan

2. High Speed: With slow acceleration and deceleration, a shake is sometimes noticed in the steering wheel/steering column tube, seats, floorpan, trim panels, or front end sheet metal. It is a low frequency vibration. It may or may not be increased by applying brakes lightly. Refer to Pinpoint Test B. B: Idle Boom/Shake/Vibration

3. High Speed: A vibration is felt in the floorpan or seats with no visible shake, but with an accompanying sound or rumble, buzz, hum, drone, or booming noise. Coast with transmission control selector lever in NEUTRAL and engine idling. If vibration is still evident, it may be related to:
- Wheels.
- Tires.
- Front disc brake rotors.
- Rear disc brake rotors.
- Wheel hubs.
- Wheel bearings.
- Axle companion flange runout.
- Driveshaft balance.

4. High Speed: A vibration is felt whenever the engine reaches a particular RPM. It will disappear in NEUTRAL coast. The vibration can be duplicated by operating the engine at the problem RPM while the vehicle is parked. It can be caused by any number of components. Refer to Pinpoint Test D. D: Non-Axle Noise

Road Conditions
The type of road and its surface condition are important factors in the road test. A smooth asphalt road that allows driving over a range of speeds is best. The brushed concrete road surface found on many expressways and the coarse aggregate sometimes found in concrete can mask many vehicle noises and make NVH diagnosis difficult.

Vehicle Preparation
1. Check and verify if vehicle is equipped with original equipment, type, size, and brand wheels and tires. If non-original equipment wheels and/or tires are installed, it may be necessary to substitute original equipment level tire/wheel assemblies to eliminate this factor before proceeding with the NVH diagnosis.
2. Check and set tire pressure.
3. Remove any externally mounted accessories such as luggage racks, magnetic base, or the antenna which may cause wind noise that interferes with NVH diagnosis.
4. A tachometer should be used.
5. Note the fuel level. Some vehicles change in their response to various excitations when the fuel level changes.
6. Try to duplicate the conditions with the customer present, particularly the speed and throttle operation.
7. Find the speed where the concern is most severe.
8. Turn the air conditioning system OFF and ON to isolate air conditioning system impact on the noise. Accelerate gently through this speed to a few mph above it and then coast back down a few mph below it and note if the concern changes.
9. Repeat this procedure, if necessary, to get a feeling for the behavior. Then drive about five mph above the speed, put the transmission in neutral, and coast down. Note any change in behavior.
10. Try "floating" the driveline by backing off slightly on the throttle at the problem speed. The idea is to unload the axle gears and the universal joints as much as possible. If the concern does not change in all these modes of operation, the cause may be driveline imbalance since the imbalance is not changed by the throttle position.