5: Road Test
Preliminary Inspection
5: Road Test
NOTE: It may be necessary to have the customer ride along or drive the vehicle to point out the symptom. 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 (Noise, Vibration, or Harshness) symptom, especially when a road test with the customer is not possible.
- The Heavy Acceleration Test helps to determine if the symptom is torque-related.
- The Neutral Coast Down Speed Test helps to determine if the symptom is vehicle speed-related.
- The Downshift Speed Test helps to determine if the symptom 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 symptom.
- 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 NERU (Neutral Engine Run-Up) Test and the Engine Load Test. These tests help to determine if the symptom is engine speed-related.
- The NERU (Neutral Engine Run-Up) Test is used as a follow-up test to the Downshift Speed Test when the symptom occurs at idle.
- The DERU (Drive Engine Run-Up) Load Test helps to identify vibration/noise sensitive to engine load or torque. It also helps to reproduce engine speed-related symptoms 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 symptoms.
- The Vehicle Cold Soak Procedure helps to identify symptoms 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 symptom 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 symptom is coming.
- Attempt to identify the source of the symptom.
- If the source of the symptom has been identified as a result of this test, proceed to the appropriate system for further diagnosis and repair. If the source has not been identified, continue with the road test.
Heavy Acceleration Test
To carry out this test, proceed as follows:
- Accelerate hard from 0 km/h (0 mph)-64.4 km/h (40 mph)
- Decelerate in a lower gear.
- The symptom is torque related if duplicated while carrying out this test.
- If the source of the symptom has been identified as a result of this test, proceed to the appropriate system for further diagnosis and repair. If the source has not been identified, continue with the road test.
Neutral Coast Down Speed Test
To carry out this test, proceed as follows:
- Drive at a higher rate of speed than where the symptom occurred when carrying out the Slow Acceleration Test.
- Place the transmission in NEUTRAL and coast down past the speed where the symptom occurs.
- The symptom is vehicle speed-related if duplicated while carrying out this test. This eliminates the engine and the torque converter as sources.
- If the symptom was not duplicated while carrying out this test, carry out the Downshift Speed Test to verify if the symptom is engine speed related.
- If the source of the symptom has been identified as a result of this test, proceed to the appropriate system for further diagnosis and repair. If the source has not been identified, continue with the road test.
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 symptom occurs.
- The symptom 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.
- If the source of the symptom has been identified as a result of this test, proceed to the appropriate system for further diagnosis and repair. If the source has not been identified, continue with the road test.
Steering Input Test
To carry out this test, proceed as follows:
- Drive at the speed where the symptom occurs, while making sweeping turns in both directions.
- If the symptom goes away or gets worse, the wheel bearings, hubs, U-joints (contained in the axles of 4WD (Four-Wheel Drive) applications), and tire tread wear are all possible sources.
- If the source of the symptom has been identified as a result of this test, proceed to the appropriate system for further diagnosis and repair. If the source has not been identified, continue with the road test.
Brake Test
To carry out this procedure, proceed as follows:
- With the brake released, accelerate the vehicle. While coasting (brake pedal released) to a stop in NEUTRAL, note any abnormal rate of deceleration. Abnormal deceleration could indicate a parking brake or service brake that is not fully releasing.
- Warm the brakes by slowing the vehicle a few times from 80.5 km/h (50 mph)-32.2 km/h (20 mph) using light braking applications.
- Accelerate to 88.5 km/h (55 mph)-96.6 km/h (60 mph). Moderately apply the brakes and slow the vehicle to a stop.
- A brake vibration can be felt in the steering wheel, seat or brake pedal. A brake noise can be heard upon brake application and should diminish when the brake is released. For vehicles with separate park brake shoes, noise or vibration from the parking brake system will not be affected by applying the hydraulic brakes. On these systems, the parking brake system requires inspection if a parking brake concern is suspected.
- If the source of the symptom has been identified as a result of this test, proceed to the appropriate brake system(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 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.
- If the source of the symptom has been identified as a result of this test, proceed to the appropriate system for further diagnosis and repair. If the source has not been identified, continue with the road test.
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 4,000 rpm while in PARK on FWD (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 symptom is coming from.
- Attempt to identify the source of the symptom.
- If the source of the symptom has been identified as a result of this test, proceed to the appropriate system for further diagnosis and repair. If the source has not been identified, continue with the road test.
Drive Engine Run-up (DERU) Test
WARNING: Block all wheels, set the parking brake and firmly apply the service brake to reduce the risk of vehicle movement during this procedure. Failure to follow these instructions may result in serious personal injury.
NOTE: Do not carry out the Engine Load Test for more than 5 seconds or damage to the transmission or transaxle may occur.
To carry out this test, proceed as follows:
- 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 2,000 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 symptom is definitely engine speed-related, carry out the Engine Accessory Test to narrow down the source.
- If the source of the symptom has been identified as a result of this test, proceed to the appropriate system for further diagnosis and repair. If the source has not been identified, continue with the road test.
Engine Accessory Test
WARNING: Block all wheels, set the parking brake and firmly apply the service brake to reduce the risk of vehicle movement during this procedure. Failure to follow these instructions may result in serious personal injury.
NOTE: Limit engine running time to one minute or less with belts removed or serious engine damage will result.
To carry out this test, proceed as follows:
NOTE: Use a frequency measurement tool to pinpoint accessory vibrations. A listening device, such as an EngineEAR, will also help to identify noises from specific accessories.
- Remove the accessory drive belt(s)
- Increase the engine rpm to where the symptom occurs.
- If the vibration/noise is duplicated when carrying out this test, the belt(s) and accessories are not sources.
- If the vibration/noise was not duplicated when carrying out this test, install the accessory belt(s), one at a time, to locate the source.
- If the source of the symptom has been identified as a result of this test, proceed to the appropriate system for further diagnosis and repair. If the source has not been identified, continue with the road test.
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 3 minutes.
- Park the vehicle where testing will occur. The vehicle must remain at or below the symptom temperature (if known) for 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, ABS (Anti-Lock Brake System) and air suspension system noises.
- Start the engine.
- 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 system for further diagnosis and repair. If the source has not been identified, continue with the road test.