Road Test

Road Test Form:

Road Test Form (continued):

Noise, Vibration and Harshness (NVH) diagnosis should always use a road test.

NVH usually occurs in four areas:
- Tires.
- Engine accessories.
- Suspension.
- Drivetrain.

It is important to isolate NVH concerns to the system or component that is causing the concern as soon as possible. One way to do this is to perform a road test. Road Test

Slight noise is normal for gear-driven units and must be considered normal.
1. Make notes throughout this diagnostic routine for future reference. Use the road test form that is included.
2. Road test the vehicle, and, if possible, validate the concern by reproducing it several times during the road test.
3. Perform the road test quick checks as soon as the condition is reproduced. Road Test Quick Check Results
This will identify which diagnostic procedure will be necessary to repair the symptom.
4. Do not make adjustments until a road test and a thorough visual inspection of the vehicle have been performed. Do not change tire pressure or vehicle load. This may change the symptoms that the customer described and prolong diagnosis.
5. Perform a visual inspection as part of the preliminary diagnostic routine. Note tire pressures, but do not adjust them. Note leaking fluids, loose nuts and/or bolts, or bright spots where components may be rubbing against each other. Check cargo area for unusual loads.
6. Perform the neutral engine runup (NERU) test. It helps to separate vibrations caused by the engine and vibrations caused by movement of the vehicle during a road test.
a. Connect a tachometer if the vehicle is not equipped with one.
b. Put the vehicle in N(neutral) or P(park) and do not set the parking brake or press the brake pedal.
c. Run the engine to approximately 4000 rpm and note any moans, vibrations, noises, etc., and the rpm at which they occur. Sometimes it is possible to "tune in" on these by varying the rpm to determine a precise rpm at which the concern occurs; in other cases they will appear across a broad range of rpm. This establishes a baseline against which vibrations from the road test can be measured.
d. If you suspect that the exhaust system is the cause of the concern, look for shiny places where the exhaust system is close to any other parts of the vehicle.
e. If you suspect the air conditioning system or drive belt, turn the air conditioning system on before performing the NERU test. If a noise occurs at a specific rpm, turn the air conditioning system off and on to see if the noise is connected to the air conditioning compressor or A/C system lines.
f. When conducting the road test, refer to the results of the NERU test to separate vibrations and noises caused by the engine from those caused by the drivetrain. If a vibration or noise occurs at a particular speed, try operating in another gear at the same speed. If it occurs at a particular rpm, use different gears to test the same engine rpm at different road speeds.