smallest bit of information, because it may turn out to be the most important.
2. 2. Do not touch anything until a road test and a thorough visual inspection of the
vehicle have been carried out. Leave the tire pressures and vehicle load just where
they were when the condition was first observed. Adjusting tire pressures, vehicle
load or making other adjustments may reduce the condition(s) intensity to a point
where it cannot be identified clearly. It may also inject something new into the
system, preventing correct diagnosis.
3. 3. Make a visual inspection as part of the preliminary diagnosis routine, writing down
anything that does not look right. Note tire pressures, but do not adjust them yet.
Note leaking fluids, loose nuts and bolts, or bright spots where components may be
rubbing against each other. Check the load space for unusual loads.
4. 4. Road test the vehicle and define the condition by reproducing it several times
during the road test.
5. 5. Carry out the Road Test Quick Checks as soon as the condition is reproduced. This
will identify the correct diagnostic procedure. Carry out the Road Test Quick Checks
more than once to verify they are providing a valid result. Remember, the Road
Test Quick Checks may not tell where the concern is, but they will tell where it is
not.
Road Test Quick Checks
1. 1. 24-80 km/h (15-50 mph): with light acceleration, a moaning noise is heard and
possibly a vibration felt in the front floor panel. 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 in the Driveline Noise and Vibration Symptom Chart.
2. 2. Acceleration/Deceleration: With slow acceleration and deceleration, a shake is
sometimes noticed in the steering wheel/column, seats, front floor panel, front door
trim panel 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 Idle Boom/Shake/Vibration in the Driveline Noise and Vibration Symptom
Chart.
3. 3. High Speed: A vibration is felt in the front floor panel or seats with no visible
shake, but with an accompanying sound or rumble, buzz, hum, drone or booming
noise. Coast with the clutch pedal depressed (manual transmission) or shift control
selector lever in "N" (NEUTRAL) (automatic transmission) and engine idling. If
vibration is still evident, it may be related to wheels, tires, front brake discs, wheel
hubs or front wheel bearings. REFER to Shake and Vibration While Driving in the
Driveline Noise and Vibration Symptom Chart.
4. 4. Engine rpm Sensitive: A vibration is felt whenever the engine reaches a particular
rpm. It will disappear in neutral coasts. The vibration can be duplicated by operating
the engine at the problem rpm while the vehicle is stationary. It can be caused by
any component, from the accessory drive belt to the clutch or torque converter
which turns at engine speed when the vehicle is stopped. REFER to Shake and
Vibration While Driving in the Driveline Noise and Vibration Symptom Chart.
5. 5. Noise and Vibration While Turning: Clicking, popping or grinding noises may be
due to the following:
worn, damaged or incorrectly installed front wheel bearing.