Hummer H1 (2006+). Manual — part 112

OBD-292

On-Board Diagnostics

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Inspect for the presence of an add-on engine power package. When engine horsepower or torque is increased over factory rating, a
shift flare condition may occur.

Step

Action

Value(s)

Yes

No

1

NOTE: Before clearing DTC(s) use the scan tool “Capture info”
to record Freeze Frame and Failure Records for reference, as data
will be lost when “Clear Info” function is used

Was the “On-Board Diagnostic (OBD) System Check” per-
formed?

Go to step 2.

Go to OBD Sys-

tem Check.

2

Measure the transmission fluid level. Refer to Transmission Fluid
Checking Procedure.

Is the transmission fluid level correct?

Go to Step 3

Go to Transmis-

sion Fluid

Checking Proce-

dure

3

1.

Install the scan tool.

2.

Start the engine.

NOTE:

• Before clearing the DTC, use the scan tool in order to

record the Freeze Frame and Failure Records for refer-
ence. The Clear Info function will erase the data.

• This diagnostic table should only be used if the DTC is

currently failing. If the DTC is not active, refer to Test-
ing for Intermittent Conditions and Poor Connections
in Wiring Systems until the DTC becomes active.

3.

Record the DTC Freeze Frame and Failure Records.

4.

Clear the DTC.

5.

Using the scan tool, measure ignition voltage.

Is voltage within the specified range?

9-18 Volts

Go to Step 4

Go to DTC

P0562 for low

voltage or DTC

P0563 for high

voltage

4

1.

Start the engine.

2.

Drive the vehicle under normal operating conditions.

3.

Using the scan tool, monitor engine, turbine and output
speed sensor readings.

Is speed sensor data erratic?

Go to the appro-

priate speed sen-

sor DTC

Go to Step 5

5

1.

Connect a 2,000 kPa (300 psi) pressure gage to the line pres-
sure tap.

2.

Use the scan tool in clutch test mode, to cycle through all
transmission ranges with the engine at idle and vehicle
brakes applied. Record line pressure in each range.

Was the line pressure low in a specific range or in ranges where
the same clutch was applied?

Go to Low Main

Line Pressure in

All Ranges

Go to Step 6

6

Conduct a clutch test for all forward ranges. Refer to Clutch Test

Did turbine speed remain at zero in all ranges?

Go to Diagnos-

tic Aids

Go to Step 7

7

1.

Remove the transmission oil pan. Refer to Automatic Trans-
mission Fluid/Filter Replacement.

2.

Inspect for signs of clutch failure.

Are there signs of a clutch failure?

Go to Step 8

Go to Step 9

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On-Board Diagnostics OBD-293

5745804

8

Remove the transmission for overhaul or replacement. Refer to
Transmission Replacement.

Did you complete the repair or replacement?

Go to Step 11

9

Inspect for a stuck or sticking PC valve.

Did you find and repair a valve condition?

Go to Step 11

Go to Step 10

10

Replace faulty PC solenoid A.

Did you complete the replacement?

Go to Step 11

11

Perform the following procedure in order to verify the repair:

1.

Clear the DTC.

2.

Start the engine.

3.

Use the scan tool to reset adaptive values for all shifts.

4.

Operate the vehicle in all ranges under normal driving condi-
tions.

5.

Select Specific DTC.

6.

Enter DTC P0746.

Has the test run and passed?

System OK

Go to Step 1

Step

Action

Value(s)

Yes

No

OBD-294

On-Board Diagnostics

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DTC P0748 Pressure Control Solenoid Circuit Electrical (Figures OBD-76, and 77)

Figure OBD-76: External Fuse Box Circuit

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On-Board Diagnostics OBD-295

5745804

Figure OBD-77: Pressure Control Solenoid Circuit

Circuit Description

Pressure control (PC) solenoid A is used to control oncoming, off-going, and holding pressure to any one of the five clutches. This
solenoid is referred to as a pressure proportional to current (PPC) solenoid since the output hydraulic pressure supplied by this so-
lenoid is proportional to the controlled current command.

The solenoid operates using a very high frequency pulse width modulation signal of 1,000 Hz. Unlike the torque converter clutch
pulse width modulated (TCC PWM) solenoid, where the ball follows the pulse width square wave, the PPC ball remains stationary.
The ball clearance is balanced between a coil current force on one side of the ball and the clutch trim pressure force on the other
side of the ball. The ball-to-seat clearance adjusts the bleed-off rate in the signal pocket. At high bleed levels, the resulting flow
across the feed orifice results in a high pressure drop. This produces the desired signal pressure level used to trim the clutch.

DTC P0748 is a type A DTC.