5: Road Test

The following is a brief overview of each test. A review of this information helps to quickly identify the most appropriate process necessary to make a successful diagnosis. After reviewing this information, select and carry out the appropriate test(s), proceeding to the next step of this process.

• The Slow Acceleration Test is normally the first test to carry out when identifying an NVH concern, especially when a road test with the customer is not possible.
• The Heavy Acceleration Test helps to determine if the concern is torque-related.
• The Neutral Coast Down Speed Test helps to determine if the concern is vehicle speed-related.
• The Steering Input Test helps to determine how the wheel bearings and other suspension components contribute to a vehicle speed-related concern.
• The Brake Test helps to identify vibrations or noise that are brake related.
• The Road Test Over Bumps helps isolate a noise that occurs when driving over a rough or bumpy surface.
• To identify if the noise is coming from the electric motor and /or gearbox (such as for a whine issue), it can be helpful sometimes to shift into neutral while driving while the condition is present.
• The Vehicle Cold Soak Procedure helps to identify concerns occurring during initial start-up and when an extended time lapse occurs between vehicle usage.

Slow Acceleration Test 

To carry out this test, proceed as follows:

• Slowly accelerate to the speed where the reported concern occurs. Note the vehicle speed, and if possible, determine the vibration frequency.
• Attempt to identify what part of the vehicle the concern is coming from.
• Attempt to identify the source of the concern.
• Proceed as necessary.

Heavy Acceleration Test 

To carry out this test, proceed as follows:

• Accelerate hard from 0-64 km/h (0-40 mph).
• Decelerate in a lower gear.
• The concern is torque related if duplicated while carrying out this test.
• Proceed as necessary.

Neutral Coast Down Speed Test 

To carry out this test, proceed as follows:

• Drive at a higher rate of speed than where the concern occurred when carrying out the Slow Acceleration Test.
• Place the transmission in NEUTRAL and coast down past the speed where the concern occurs.
• The concern is vehicle speed-related if duplicated while carrying out this test. This eliminates the engine or motor as a source.
• Proceed as necessary.

Steering Input Test 

To carry out this test, proceed as follows:

• Drive at the speed where the concern occurs, while making sweeping turns in both directions.
• If the concern goes away or gets worse, the wheel bearings, hubs and tire tread wear are all possible sources.
• Proceed as necessary.

Brake Test 

To carry out this test, proceed as follows:

• Warm the brakes by slowing the vehicle a few times from 80-32 km/h (50-20 mph) using light braking applications. At highway speeds of 89-97 km/h (50-60 mph), apply the brake using a light pedal force.
• Accelerate to 89-97 km/h (55-60 mph).
• Lightly apply the brakes and slow the vehicle to 30 km/h (20 mph).
• A brake vibration noise can be felt in the steering wheel, seat or brake pedal. A brake noise can be heard upon brake application and diminish when the brake is released.
• If the source of the symptom has been identified as a result of this test, proceed to the appropriate brake article(s) for further diagnosis and repair. If the source has not been identified, continue with the road test.

Road Test Over Bumps 

To carry out this test, proceed as follows:

• Drive the vehicle over a bumpy or rough surface one wheel at a time to determine if the noise is coming from the front or the back and the left or the right side of the vehicle.
• Proceed as necessary.

Vehicle Cold Soak Procedure 

To carry out this procedure, proceed as follows:

• Test preparations include matching the customer conditions (if known). If not known, document the conditions. Monitor the vibration/noise duration with a watch for up to 3 minutes.
• Park the vehicle where testing will occur. The vehicle must remain at or below the concern temperature (if known) for 6-8 hours.
• Before starting the vehicle, conduct a visual inspection under the hood.
• Listen for pumps that circulate coolant for motor, electronics, heater and battery.
• NOTE: Never probe moving parts.

  Isolate the vibration/noise by carefully listening. Move around the vehicle while listening to find the general location of the vibration/noise. Then, search for a more precise location by using a stethoscope or EngineEAR.

• If the source of the symptom has been identified as a result of this test, proceed to the appropriate article for further diagnosis and repair. If the source has not been identified, continue with the road test.