B. Road Testing Vehicle For Torque Converter Shudder

B. Road Testing The Vehicle For Torque Converter Shudder/Buzz:

WARNING:
Have an assistant drive the vehicle during the vehicle road test, while the technician operates the StarSCAN(R) scan tool and monitors its data. Obey all traffic regulations. A smooth black top pavement is the preferred road surface for evaluation. The vehicle will need to be accelerated safely, at light throttle, from 56 to 80 km/h (35 to 50 mph).

NOTE:
The shudder/buzz condition is usually much more detectable while the transmission is cold (below normal operating temperature).

1. Connect the StarSCAN(R) scan tool to the vehicle Data Link Connector (DLC).

2. Using the StarSCAN(R), navigate to the ECU view, select TCM EGS 52, and select the Data Display screen.

3. Scroll to the Torque Converter Clutch (TCC) data information screen. The screen will display the following:

a. "TCC Duty Cycle"

b. "TCC Status"

c. "TCC Actual Slip"

d. "TCC Desired Slip"

e. "TCC Setpoint Pressure"

f. "Actual Gear"

g. "Target Gear"

4. With an assistant driving, accelerate the vehicle to 56 km/h (35 mph).

5. Verify that the transmission ("Actual Gear") is in either 4th or 5th gear.

6. Continue slowly accelerating the vehicle until the "TCC Status" changes from "OPEN" to "SLIP" mode.

7. While the transmission is in 4th or 5th gear and in "SLIP" mode, carefully evaluate the vehicle for the presence of a shudder vibration or an audible high frequency buzz-like sound. The shudder/buzz is most noticeable in 4th or 5th gear at vehicle speeds between 64 to 80 km/h (40 to 50 mph).

a. Under normal operation, the "TCC Actual Slip" value will change/modulate between 40 to 80 RPM's of slip.

b. When the shudder/buzz condition is present, the "TCC Actual Slip" value will change/modulate between 0 to 80 RPM's of slip. At 0 RPM's the TCC is not slipping as intended (sticking). The change between 0 RPM's and 80 RPM's may cause a "stick slip" shudder condition and/or an associated vibration induced buzz-like sound.

8. The shudder/buzz condition may not occur during the first evaluation attempt. Repeat steps 4 through 7 three more times to confirm the shudder/buzz condition. The engine and transmission may need to be brought up to normal operating temperatures to thoroughly diagnose. It is important to make certain that the transmission shudder/buzz condition is caused by the stick-slip of the transmission torque converter, and not some other vehicle component.

9. Did the road test confirm the presence of a transmission torque converter clutch shudder/buzz condition when the torque converter was in its "SLIP" mode?

a. If YES >> Proceed to Section D - Torque Converter Replacement. The torque converter must be replaced and the old transmission oil thoroughly flushed from the transmission.

b. If NO >> Proceed to Section E - Transmission Oil Drain. The old transmission oil must be thoroughly flushed from the transmission. The torque converter does not require replacement.

NOTE:
If the shudder/buzz condition occurs when the transmission torque converter is NOT in "SLIP" mode, then this Service Bulletin does not apply and further diagnosis is required.