Hummer H2. Manual - part 2616

does not flow through the transmission oil cooler and pipes, the cause of the blockage must be diagnosed 
and the plugged component must be repaired or replaced. Continue with the cooler flushing and flow 
check procedure once the blockage is corrected.  

6. Turn the flusher water supply valve (1) to the OFF position and clip the discharge hose onto a 5 gallon 

pail with a lid, to avoid splashback. 

7. Turn the flusher water supply valve (1) to the ON position and depress the trigger (8) to mix cooler 

flushing solution into the water flow. Use the clip provided on the handle to hold the trigger (8) down. 
See Fig. 10 . The discharge will foam vigorously when the solution is introduced into the water stream.  

8. Flush the transmission oil cooler and pipes with water and solution for 2 minutes. During this flush, 

attach the shop air supply 120 psi (825 kPa) to the flushing system feed air valve (2) located on the 
flusher, for 3-5 seconds at the end of every 15-20 second interval to create a surging action.  

9. Release the trigger (8) and turn the flusher water supply valve (1) to the OFF position.  

NOTE:

Flushing for approximately 2 minutes in each cooler line direction will 
result in a total of about 8-10 gallons of waste fluid. This mixture of water 
and flushing fluid is to be captured in a bucket or similar container. 

 

2004 Hummer H2 

2003-04 AUTOMATIC TRANSMISSIONS Servicing - H2

  

Fig. 10: Flushing Transmission Oil Cooling System 
Courtesy of GENERAL MOTORS CORP. 

Forward Flush 

1. Disconnect both hoses (3 and 5) from the transmission oil cooler pipes and connect them to the opposite 

transmission oil cooler pipe. See Fig. 9 . This will allow the transmission oil cooler and pipes to be 
flushed in the normal flow direction.  

2. Repeat Steps 6 and 7 of BACK FLUSH procedure.  

3. Release the trigger (8) of the transmission oil cooler and line flusher and allow water only to rinse the 

transmission oil cooler and pipes for one minute. See Fig. 10 . 

 

2004 Hummer H2 

2003-04 AUTOMATIC TRANSMISSIONS Servicing - H2

  

4. Turn the flusher water supply valve (1) to the OFF position and turn OFF the water supply at the faucet.  

5. Attach the shop air supply to the flushing system feed air valve (2) on the flusher and blow out the water 

from the transmission oil cooler and pipes. Continue, until no water comes out of the discharge hose.  

Flow Test 

1. Disconnect the hose from the transmission oil cooler pipe. Connect the transmission oil cooler feed pipe, 

bottom connector, to the transmission for normal flow.  

2. Clip the discharge hose (1) to an empty transmission container. See Fig. 11 .  

3. Confirm the transmission is filled with automatic transmission fluid. See FLUID CAPACITIES for 

correct fluid capacity.  

4. Start the engine with the transmission in Park range and run for 30 seconds after fluid begins to flow from 

the discharge hose (1). A minimum of 2 qt (1.9 L) must be discharged during this 30 second run time.  

5. If the fluid flow meets or exceeds 2 qts (1.9 L) in 30 seconds, connect the transmission oil cooler feed 

pipe to the bottom connector on the transmission.  

6. If fluid flow is less than 2 qt (1.9 L) in 30 seconds, perform the following diagnosis: 

A. Disconnect the transmission cooler and line flusher discharge hose (1) from the transmission oil 

cooler return pipe.  

B. Disconnect the transmission cooler feed pipe at the radiator.  

C. Connect the flusher discharge hose (1) to the transmission cooler feed pipe, radiator end.  

D. Clip the discharge hose (1) onto the transmission drain container.  

E. Start the engine with the transmission in Park range and run for 30 seconds after fluid begins to 

flow from the discharge hose (1). A minimum of 2 qt (1.9 L) must be discharged during this 30 
second run time.  

7. If the amount of transmission fluid flow remains less than 2 qt (1.9 L) in 30 seconds, inspect the 

transmission oil cooler feed pipe, bottom connector, for restrictions or damage. If no condition is found 
with the feed pipe, bottom connector, inspect the transmission. 

NOTE:

The Flow Test must be performed after the flush to ensure that all flushing 
solution and water is removed from the transmission oil cooling system. 

 

2004 Hummer H2 

2003-04 AUTOMATIC TRANSMISSIONS Servicing - H2

  

Fig. 11: Capturing Fluid Discharge 
Courtesy of GENERAL MOTORS CORP. 

Clean-Up 

1. Disconnect the water supply hose from the transmission cooler and line flusher and bleed any remaining 

air pressure from the flusher tank.  

2. Remove the fill cap from the flusher and return any unused flushing solution to its container. Rinse the 

flusher with water. DO NOT store the flusher with flushing solution in it.  

3. After every third use, clean the flusher as described in the instructions included with the tool.  

4. Dispose of any waste water/solution and transmission fluid in accordance with local regulations.  

ON-VEHICLE REPAIRS 

NOTE:

Various components may be serviced without transmission removal, depending 
on application. For servicing of these components, see appropriate component 
under ADJUSTMENTS and/or REMOVAL & INSTALLATION . For additional 
information on testing electrical components, see appropriate DIAGNOSIS 
article. 

 

2004 Hummer H2 

2003-04 AUTOMATIC TRANSMISSIONS Servicing - H2