Road Test Quick Checks

Road Conditions
The road is an important factor 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 diagnosis difficult.

If the customer complains of a noise or vibration on a particular road and only on a particular road, the source of the concern may be the road surface. If possible, try to test on the same type of surface. This is the only case where a smooth asphalt road may not be best.

Vehicle Preparation
1. Check and verify if the vehicle is equipped with original equipment, type, size and brand wheels and tires. If non-original equipment wheels or tires are installed, it may be necessary to substitute the original equipment level tire/wheel assemblies for the diagnosis.
2. Check and set the tire pressure.

Quick Checks
1. 24-80km/h (15-50 mph): With light acceleration, a moaning noise is heard and possibly a vibration is felt in the floor pan. It is usually worse at a particular engine speed and at a particular throttle setting during acceleration at that speed. It may also produce a moaning sound, depending on what component is causing it.
Refer to Tip-In Moan. B: Tip-In Moan

2. 40-72 km/h (25-45 mph): With steady to heavy acceleration or deceleration, a rumble-type noise is heard. It is very intense during heavy acceleration or deceleration and very light during cruise or neutral coast. The vibration is hard to duplicate with the vehicle supported on a hoist, since the wheels are coasting free.
Refer to Driveshaft Vibration. D: Driveshaft Vibration

3. High Speed: With slow acceleration and deceleration or at a constant speed, a shake is sometimes noticed in the steering wheel/column, seats, floor pan, trim panels or front-end sheet metal. It is a low-frequency vibration (around 9-15 cycles per second). It may or may not be increased by applying the brakes lightly.
Refer to High Speed Shake. A: High Speed Shake

4. High Speed: A vibration is felt in the floor pan or seats with no visible shake, but with an accompanying sound or rumble, buzz, hum, drone or booming noise.
It will exist in all drive modes but may vary somewhat in acceleration, deceleration, float or coast modes. In some cases, the driveline vibration is eliminated in the float mode.
Refer to Driveshaft Vibration. D: Driveshaft Vibration

5. 0-High Speed: A vibration is felt whenever the engine reaches a particular rpm. The vibration can be duplicated by operating the engine at the problem rpm while the vehicle is sitting still. It can be caused by any component that turns at engine speed when the vehicle is stopped.
Refer to Engine Accessory Vibration. C: Engine Accessory Vibration