Hummer H2. Manual — part 2427

DTC P0748

steady acceleration, with a TP angle at
20%.

While the scan tool TCC Enable status is NO,
does the scan tool display a TCC Slip Speed
within the specified range?

Go to Step 3

Go to Diagnostic

Aids

3

The TCC is hydraulically stuck ON. Inspect
for the following:

z

Clogged exhaust orifice in the TCC
solenoid valve.

z

Converter clutch apply valve stuck in the
apply position.

z

Misaligned or damaged valve body
gasket.

z

Restricted release passage.

z

Restricted transmission cooler line.

Did you find and correct the condition?

-

Go to Step 4

-

4

Perform the following procedure in order to
verify the repair:

1. Select DTC.

2. Select Clear Info.

3. Drive the vehicle in D4 with the TCC

OFF and the throttle above 17%. Ensure
that the scan tool TCC Slip Speed is
100-2,000 RPM for 5 seconds.

4. Select Specific DTC.

5. Enter DTC P0742.

Has the test run and passed?

-

Go to Step 5

Go to Step 2

5

With the scan tool, observe the stored
information, capture info, and DTC Info.
Does the scan tool display any DTCs that you
have not diagnosed?

-

Go to Diagnostic

Trouble Code

(DTC) List in

Engine Controls -

6.0L (LQ4)

System OK

2004 Hummer H2

2004 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E Diagnosis (DTC P0218 To DTC P2771) - Hummer H2

Fig. 13: Pressure Control (PC) Solenoid Valve Diagram
Courtesy of GENERAL MOTORS CORP.

Circuit Description

The pressure control (PC) solenoid valve is an electronic device that regulates transmission line pressure based
on the current flow through its coil winding. The magnetic field produced by the coil moves the solenoid's
internal valve which varies pressure to the pressure regulator valve. The powertrain control module (PCM)

2004 Hummer H2

2004 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E Diagnosis (DTC P0218 To DTC P2771) - Hummer H2

controls the PC solenoid valve by applying a varying amount of amperage to the solenoid. The applied
amperage can vary from 0.1 to 1.1 amps. Low amperage, 0.1 amp, indicates high line pressure. High amperage,
1.1 amps, indicates low line pressure. The duty cycle of the PC solenoid valve is expressed as a percentage of
energized ON time. Zero percent indicates zero ON time, non-energized, or no current flow. Approximately 60
percent at idle indicates maximum ON time, energized, or high current flow. The PCM determines the
appropriate line pressure for a given load by comparing the throttle position sensor voltage, the engine speed
and other inputs.

When the PCM detects a continuous open or short in the PC solenoid valve circuit, then DTC P0748 sets. DTC
P0748 is a type C DTC.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

The PC solenoid valve duty cycle reaches its high limit, approximately 95 percent, or low limit, approximately
0 percent.

Action Taken When the DTC Sets

z

The PCM does not illuminate the malfunction indicator lamp (MIL).

z

The PC solenoid valve is OFF.

z

The PCM freezes transmission adaptive functions.

z

The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM
stores this information as Failure Records.

z

The PCM stores DTC P0748 in PCM history.

Conditions for Clearing the DTC

z

A scan tool can clear the DTC.

z

The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without a non-
emission-related diagnostic fault occurring.

z

The PCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is
OFF long enough in order to power down the PCM.

Diagnostic Aids

DTC P0748 may set under low voltage conditions caused by high electrical system demands.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

2: This step tests the ability of the PCM to command the PC solenoid valve.

2004 Hummer H2

2004 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E Diagnosis (DTC P0218 To DTC P2771) - Hummer H2

3: This step tests the PC solenoid valve and automatic transmission wiring harness assembly for incorrect
resistance.

DTC P0748

Step

Action

Value

(s)

Yes

No

1

Did you perform the Diagnostic System Check
- Engine Controls?

-

Go to Step 2

Go to Diagnostic

System Check -

Engine Controls in

Engine Controls -

6.0L (LQ4)

2

1. With a scan tool.

2. Turn ON the ignition, with the engine

OFF.

3. Record the DTC Failure Records.

4. Clear the DTC.

5. Start the engine.

6. Use the scan tool in order to command

0.1 amp through 1.0 amp while
observing PC Sol. Ref. Current and PC
Sol. Actual Current.

Is the PC Sol. Actual Current always within the
specified value of the PC Sol. Ref. Current?

IMPORTANT:

Before clearing the DTC, use the scan
tool in order to record the Failure
Records. Using the Clear Info function
erases the Failure Records from the
PCM.

0.16
amp

Go to Intermittent

Conditions in

Engine Controls -

6.0L (LQ4)

Go to Step 3

3

1. Turn OFF the ignition.

2. Disconnect the AT inline 20-way

connector.

3. Install the J 44152 Jumper Harness (20

pins) on the transmission side of the AT
inline 20-way connector.

4. Using the DMM and the J 35616 GM

Terminal Test Kit, measure the resistance
between terminals C and D of the J
44152 .

Refer to Automatic Transmission

3-7

ohm

2004 Hummer H2

2004 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E Diagnosis (DTC P0218 To DTC P2771) - Hummer H2