Hummer H1 (2006+). Manual - part 111

OBD-288

On-Board Diagnostics

_____________________________________________

DTC P0746 Pressure Control Solenoid Performance

Circuit Description

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

The transmission control module (TCM) uses information from the turbine speed sensor and output speed sensor (OSS) to detect if
a clutch is slipping. The clutch being controlled by the PC solenoid A will vary depending on the shift that was being completed.

DTC P0746 is a type A DTC.

Conditions for Setting the DTC

DTC P0746 sets when the TCM detects an incorrect oncoming ratio, for an accumulated number of occurrences during a forward
range shift.

Action Taken When the DTC Sets 

•   The TCM illuminates the malfunction indicator lamp (MIL). 

•   When failure occurs in a forward range, the transmission will go to the previous range. If failure occurs in NEUTRAL or 

REVERSE, the transmission will lock in NEUTRAL while diagnostic response is active. 

•

If the shift selector is moved to NEUTRAL, the transmission will shift to NEUTRAL and in some cases may lock in NEU-

TRAL.

•   If the shift selector is moved to REVERSE, the transmission will shift to REVERSE or NEUTRAL. 

•   If the shift selector is returned to a forward range and the transmission is compromised by over speeding or direction 

change, the transmission will shift to NEUTRAL. 

•   DTC P0746 will be stored in TCM history. 

•   The TCM freezes shift adapts. 

•   The TCM inhibits torque converter clutch (TCC) engagement. 

Conditions for Clearing the DTC

A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle com-
pletes 40 warm-up cycles without failure.

Diagnostic Aids 

•   Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions: 

•   A bent terminal 

•   A backed-out terminal 

•   A damaged terminal 

•   Poor terminal tension 

•   A chafed wire 

•   A broken wire inside the insulation 

•   When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a 

change.

•   You may have to drive the vehicle in order to experience a condition. 

•   This DTC indicates the oncoming clutch being controlled by the PC solenoid A, not applied or applied too slowly. This 

could indicate a leak or obstruction in a specific clutch apply circuit. Observe scan tool failure record data for previous or 
current range information when the DTC was set, to determine specific shift when the DTC was set. Refer to the Sole-
noid and Clutch Chart to determine which clutch circuit is suspect. 

_____________________________________________

 On-Board Diagnostics  OBD-289

5745804

NOTE:  Clutch failure due to installation of an engine power upgrade is not covered under the manufacturers warranty. 

• 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. Refer to Line Pressure Check Procedure.

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 

OBD-290

On-Board Diagnostics

_____________________________________________

    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

    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

_____________________________________________

 On-Board Diagnostics  OBD-291

5745804

DTC P0747 Pressure Control Solenoid Stuck On

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 transmission control module (TCM) uses information from the turbine and output speed sensors to detect if a clutch is in a tie-
up condition or 3 clutches are applied. The clutch being controlled by PC solenoid A will vary depending on the shift being made.

DTC P0747 is a type A DTC.

Conditions for Setting the DTC

DTC P0747 sets if the TCM determines off-going clutch controlled by PC solenoid A remains engaged during a forward range
shift.

Action Taken When the DTC Sets 

•   The TCM illuminates the malfunction indicator lamp (MIL). 

•   When failure occurs in a forward range, the transmission will go to the previous range. If failure occurs in NEUTRAL or 

REVERSE, the transmission will lock in NEUTRAL while diagnostic response is active. 

•   If the shift selector is moved to NEUTRAL, the transmission will shift to NEUTRAL. 

•

If the shift selector is moved to REVERSE, the transmission will shift to REVERSE or NEUTRAL, or in some cases may 

lock in NEUTRAL. 

•   If the shift selector is returned to a forward range and the transmission is compromised by over speeding or direction 

change, the transmission will shift to NEUTRAL. 

•   DTC P0747 will be stored in TCM history. 

•   The TCM freezes shift adapts. 

•   The TCM inhibits torque converter clutch (TCC) engagement. 

Conditions for Clearing the DTC

A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle com-
pletes 40 warm-up cycles without failure.

Diagnostic Aids 

•   Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions: 

•   A bent terminal 

•   A backed-out terminal 

•   A damaged terminal 

•   Poor terminal tension 

•   A chafed wire 

•   A broken wire inside the insulation 

•   When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a 

change.

•  You may have to drive the vehicle in order to experience a condition. 

•  This DTC indicates the off-going clutch being controlled by PC solenoid A, is not releasing or is slow to release. This 

could indicate a leak or obstruction in a specific clutch apply circuit. Observe scan tool failure record data for previous or 
current range information when the DTC was set, to determine the specific shift when the DTC was set. Refer to Sole-
noid and Clutch Chart to determine which clutch circuit is suspect. 

NOTE:   Clutch failure due to installation of an engine power upgrade is not covered under the manufacturers warranty.