Road Test

NOTE: It may be necessary to have the customer ride along or drive the vehicle to point out the concern. During the road test, take into consideration the customer's driving habits and the driving conditions. The customer's concern just may be an acceptable operating condition for that vehicle.

The following is a brief overview of each test in the order in which it appears. 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 Downshift Speed Test helps to determine if the concern is engine 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.
• The Engine Run-Up Tests consist of the Neutral Run-Up Test and the Engine Load Test. These tests help to determine if the concern is engine speed-related.
• The Neutral Run-Up Test is used as a follow-up test to the Downshift Speed Test when the concern occurs at idle.
• The Engine Load Test helps to identify vibration/noise sensitive to engine load or torque. It also helps to reproduce engine speed-related concerns that cannot be duplicated when carrying out the Neutral Run-Up Test or the Neutral Coast Down Test.
• The Engine Accessory Test helps to locate faulty belts and accessories that cause engine speed-related concerns.
• 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, the engine rpm and, if possible, determine the vibration frequency.
• Attempt to identify from what part of the vehicle the concern is coming.
• 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 and the torque converter as sources.
• If the concern was not duplicated while carrying out this test, carry out the Downshift Speed Test to verify if the concern is engine speed related.
• Proceed as necessary.

Downshift Speed Test

To carry out this test, proceed as follows:

• Shift into a lower gear than the gear used when carrying out the Slow Acceleration Test.
• Drive at the engine rpm where the concern occurs.
• The concern is engine speed related if duplicated while carrying out this test. This eliminates the tires, wheels, brakes and the suspension components as sources.
• If necessary, repeat this test using other gears and NEUTRAL to verify the results.
• 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, U-joints (contained in the axles of 4WD applications), 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.

Road Test Over Bumps

To carry out this test, proceed as follows:

• Drive the vehicle over a bump 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.

Neutral Engine Run-Up (NERU) Test

To carry out this test, proceed as follows:

• Install a tachometer.
• Increase the engine rpm up from an idle to approximately 4000 rpm while in PARK on front wheel drive vehicles with automatic transmissions, or NEUTRAL for all other vehicles. Note the engine rpm 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.

Drive Engine Run-Up (DERU) Load Test

To carry out this test, proceed as follows:

• WARNING: Block the front and rear wheels, and apply the parking brake and the service brake, or injury to personnel can result.

  CAUTION: Do not carry out the Engine Load Test for more than five seconds or damage to the transmission or transaxle can result.

  Block the front and rear wheels.

• Apply the parking brake and the service brake.
• Install a tachometer.
• Shift the transmission into DRIVE, and increase and decrease the engine rpm between an idle to approximately 2000 rpm. Note the engine rpm and, if possible, determine the vibration frequency.
• Repeat the test in REVERSE.
• If the vibration/noise is duplicated when carrying out this test, inspect the engine and transmission or transaxle mounts.
• If the concern is definitely engine speed-related, carry out the Engine Accessory Test to narrow down the source.
• Proceed as necessary.

Engine Accessory Test

To carry out this test, proceed as follows:

• WARNING: Block the front and rear wheels, and apply the parking brake and the service brake, or injury to personnel can result.

  CAUTION: Limit engine running time to one minute or less with belts removed or serious engine damage will result.

NOTE: A serpentine drive belt decreases the usefulness of this test. In these cases, use a vibration analyzer, such as the VA, to pinpoint accessory vibrations. An electronic listening device, such as an EngineEAR, will also help to identify noises from specific accessories.

Remove the accessory drive belts.

• Increase the engine rpm to where the concern occurs.
• If the vibration/noise is duplicated when carrying out this test, the belts and accessories are not sources.
• If the vibration/noise was not duplicated when carrying out this test, install each accessory belt, one at a time, to locate the source.

Vehicle Cold Soak Procedure

To carry out this procedure, proceed as follows:

• Test preparations include matching customer conditions (if known). If not known, document the test conditions: gear selection and engine rpm. Monitor the vibration/noise duration with a watch for up to three 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 engine, conduct a visual inspection under the hood.
• Turn the key on, but do not start the engine. Listen for the fuel pump, anti-lock brake system (ABS) and air suspension system noises.
• Start the engine.
• CAUTION: 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.

• GO to Symptom Chart - Idle Noise/Vibration to assist with the diagnosis.

6: Check OASIS/TSBs/Repair History

After verifying the customer concern, check for OASIS reports, TSBs and the vehicle repair history for related concerns. If information relating to a diagnosis/repair is found, carry out the procedure(s) specified in that information.

If no information is available from these sources, carry out the vehicle preliminary inspection to eliminate any obvious faults.

7: Diagnostic Procedure

Qualifying the concern by the particular sensation present can help narrow down the concern. Always use the "symptom" to "system" to "component" to "cause" diagnosis technique. This diagnostic method divides the problem into related areas to correct the customer concern.

• Verify the "symptom".
• Determine which "system(s)" can cause the "symptom".

• If a vibration concern is vehicle speed related, the tire and wheel rpm/frequency or driveshaft frequency should be calculated.
• If a vibration concern is engine speed related, the engine, engine accessory or engine firing frequencies should be calculated.

• After determining the "system", use the diagnostic tools to identify the worn or damaged "components".
• After identifying the "components", try to find the "cause" of the failure.

Once the concern is narrowed down to a symptom/condition, proceed to NVH Condition and Symptom Categories.