Hummer H1 Service Manual page 324

___________________________________________
®
Electrical/Garage Shift Test
Perform this test before a road test in order to make sure that
electronic control inputs are connected and operating. If you do
not check the inputs before operating the transmission, you
could misdiagnose a simple electrical condition as a major
transmission condition.
A scan tool provides valuable information. Use the scan tool
on the transmission for accurate diagnosis.
1. Move the gear selector to Park and set the parking brake.
2. Connect the scan tool to the DLC connector.
3. Start the Engine
4. Verify that the following signals are present on the scan
tool:
• Transmission Input (shaft) Speed Sensor (A/T ISS)
• Transmission Output(shaft) Speed Sensor (VSS)
• Automatic Transmission Fluid Pressure Manual Valve
Position Switch (TFP val.)
• Vehicle speed
• Current Gear
• Reference Transmission Pressure Control Solenoid Am-
perage (Ref Current)
• Actual Transmission Pressure Control Solenoid Amper-
age (ACT CURRENT)
• Engine Coolant Temperature (ECT)
• Automatic Transmission Fluid Temperature Signal
(TFT)
• APP angle
• TCC duty cycle (TCC DC)
• System Voltage
• TCC Brake Switch
5. Monitor the TCC BRAKE signal with the scan tool while
tapping the brake pedal with your foot. The brake switch
signal should be:
• Open - when the brake pedal is released
• Closed - when the brake pedal is depressed
6. Monitor the Automatic Transmission Fluid Pressure
Manual Valve Position Switch signal by moving the gear
selector through all of the ranges. Verify that the FRP
Switch state matches the gear range which is indicated on
the instrument panel or on the console. Gear selections
should be immediate and not harsh.
7. Move the gear selector to Neutral and monitor the APP
angle while increasing and decreasing engine RPM with
the accelerator pedal. The Throttle angle should increase
with the engine RPM.
Torque Converter Clutch Diagnosis
The Torque Converter Clutch (TCC) is applied by fluid pres-
sure, which is controlled by a PWM solenoid valve. This sole-
noid valve is located inside of the automatic transmission
05745159
Transmission/Transfer Case
assembly. The solenoid valve energizes or de-energizes by
making or breaking an electrical circuit through a combination
of switches and sensors.
Torque Converter Stator
The torque converter stator roller clutch can have two different
malfunctions.
• The stator assembly freewheels in both directions
• The stator assembly remains locked up at all times
Poor Acceleration at Low Speed
If the stator is freewheeling at all times, the car tends to have
poor acceleration from a standstill. At speeds above 50 -55 km/
h (30-35 mph), the car may act normally. For poor acceleration
you should first determine that the exhaust system is not
blocked, and the transmission is in First gear when starting out.
If the engine freely accelerates to high RPM in Neutral, you
can assume that the engine and the exhaust system are normal.
Check for poor performance in Drive and Reverse to help de-
termine if the stator is freewheeling at all times.
Poor Acceleration at High Speed
If the stator is locked up at all times, performance is normal
when accelerating from a standstill. Engine RPM and car speed
are limited or restricted at high speeds. Visual examination of
the converter may reveal a blue color from overheating.
If the converter has been removed, you can check the stator
roller clutch by inserting a finger into the splined inner race of
the roller clutch and trying to turn the race in both directions.
You should be able to freely turn the inner race clockwise, but
you should have difficulty in moving the inner race counter-
clockwise or you may be unable to move the race at all.
Noise
Important: Do not confuse this noise with pump whine noise,
which is usually noticeable in Park, Neutral, and all other gear
ranges. Pump whine with vary with line pressure.
You may notice a torque converter whine when the vehicle is
stopped and the transmission is in Drive or Reverse. This noise
will increase as you increase the engine RPM. The noise will
stop when the vehicle is moving or when you apply the torque
converter clutch, because both halves of the converter are turn-
ing at the same speed.
Perform a stall test to make sure the noise is actually coming
from the converter:
1. Place your foot on the brake
2. Put the gear selector in Drive.
NOTE: You may damage the transmission if you depress the
accelerator for more than six seconds.
3. Depress the accelerator to approximately 1200 RPM for
no more than six seconds.
A torque converter noise will increase under this load.
5-125