Content .. 70 71 72 73 ..

Hummer H1 (2002+). Manual - part 72

____________________________________________

Transmission/Transfer Case 5-87

05745159

DTC P0742 Torque Converter Clutch Stuck On

Step

Action

Value

Yes

Connect scan tool.

Turn the ignition switch to on.

Record the DTC “Freeze Frame” and Failure
Records.”

Using the scan tool, verify the “TP Sensor” opera-
tion.

Are the TPS values within range shown in the value
column?

0.6 - 5.0 volts

Go to Step 2

Go to Diag-
nostic Aids

Drive vehicle in D4 drive range under steady accelera-
tion, with a throttle angle greater than 25%.

Does scan tool display “TCC Slip Speed” between -15
and +20 rpm, TCC (converter clutch) solenoid off?

—

Go to Step 3

Go to Diag-
nostic Aids

TCC converter clutch is seized in on mode, check the
following:

• Clogged exhaust orifice in the TCC solenoid.

• Converter clutch apply valve stuck in the apply

position.

• Misaligned or damaged valve body gasket.

• Restricted release passage.

—

Go to Step 4

—

After the repair is complete, use the scan tool to
select “DTC,” then “Clear Inform function.

Select “Specific DTC” and enter DTC “P0742.”

Operate the vehicle in D2, D3, or D4 with the TCC
“Off” and the throttle above 10%.

• TCC slip speed must be between 25 and 2500

rpm for 5 seconds.

—

Repair veri-
fied, exist
DTC table.

5-88

Transmission/Transfer Case

_____________________________________________

DTC P0748 Pressure Control Solenoid (PCS) - Electrical

Circuit Description

The PCS is a PCM-controlled device used to regulate transmis-
sion line pressure. The PCM compares electronic accelerator
pedal voltage, engine rpm, and other inputs to determine line
pressure appropriate for a given load. The PCM will regulate
pressure by applying a varying amperage to the PCS. The am-
perage can vary from 0.1 to 1.1 amp.

This DTC detects a continuous open or short to ground in the
PCS circuit or the PCS.

Conditions For Setting DTC

• Engine must be running for at least 5 seconds.

• Difference in commanded and measured return amper-

age is greater than 0.16 amps.

• Conditions met for 200 milliseconds.

Action Taken When DTC Sets

• The PCM will disable the PCS.

• The PCM will freeze shift adapts.

• The PCM will NOT turn on the Malfunction Indicator

Lamp (MIL).

Conditions For Clearing The DTC

• The DTC can be cleared from the PCM history by using

the scan tool. The DTC will be cleared when the vehicle
has achieved 40 warm-up cycles without a failure re-
ported.

• The PCM will cancel the DTC default actions when the

fault no longer exists and the ignition is cycled “off”
long enough to power down the PCM.

FUSE 2A

10A

EXTERIOR

C33-F

351 PK

C34

C32-G

C32-F

C32-E

C32-D

C32-C

C32-J

C32-H

C34-E

C27-C15

C27-C7

C28-C5

C28-C6

C28-C4

C29-B12

C27-C9

265 LB

264 RD

924 TN

315 YL

237 LG

359 BK

923 BR

PRESSURE

CONTROL

SOLENOID

(PCS)

TORQUE

CONVERTER

CLUTCH

SOLENOID

(TCC)

1-2 SHIFT
SOLENOID
(1-2)

2-3 SHIFT
SOLENOID
(2-3)

TRANSMISSION

FLUID

TEMPERATURE

SENSOR

(TFT)

PCS

LOW

PCS

HIGH

TCC PWM

SOLENOID

CONTROL

2-3 SS

CONTROL

1-2 SS

CONTROL

SENSOR

GROUND

TFT

SENSOR

SIGNAL

POWERTRAIN

CONTROL

MODULE

(PCM)

HOT IN RUN
AND START

____________________________________________

Transmission/Transfer Case 5-89

05745159

Diagnostic Aids

• Inspect the wiring for poor electrical connections at the

PCM and at the transmission 20-way connector. Look
for possible bent, backed out, deformed or damaged ter-
minals. Check for weak terminal tension as well. Also
check for a chafed wire that could short to bare metal or
other wiring. Inspect for a broken wire inside the insula-
tion.

• When diagnosing for a possible intermittent short or

open condition, wriggle the wiring harness while ob-
serving test equipment for a voltage change.

• If any engine DTCs or TP Sensor codes are present di-

agnose and clear these DTCs first. Then check to see if
the transmission DTCs have reset.

Test Description

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

This test checks the ability of the PCM to command
the PCS.

This test checks the PCS and internal wiring harness
for incorrect resistance

5-90

Transmission/Transfer Case

_____________________________________________

DTC P0748 Pressure Control Solenoid - Electrical

Step

Action

Value

Yes

Connect scan tool.

Turn the ignition switch to on.

NOTE: Important:

Before clearing DTC(s), use the

scan tool to record “Failure Records” for reference, as
data will be lost when the “Clear Info” function is used.

Record the DTC “Failure Records.”

Start engine and shift into Park.

Using the transmission output control function on
the scan tool, apply 0.1 amp through 1.0 amp while
observing “PC Ref. Current” and “PC Act. Cur-
rent.”

Is the “PC Act. Current” reading always within the indi-
cated value?

0.16 amp

Go to Diag-

nostic Aids

Go to Step 2

Turn ignition off.

Disconnect transmission 20-way connector.

Install the 05743837 Jumper Harness on the trans-
mission side of the 20-way connector.

Using the multimeter and Connector Test Adapter
Kit, measure the resistance between terminals “C”
and “D.”

Is the resistance within indicated values?

3-7 ohms

Go to Step 6

Go to Step 3

Remove transmission oil pan.

Disconnect wiring harness at PCS.

Measure resistance of PCS.

Is resistance within indicated values?

3-7 ohms

Go to Step 5

Go to Step 4

Replace the PCS.
Is the replacement complete?

—

Go to Step 8

—

Repair internal wiring harness for open.
Is the repair complete?

—

Go to Step 8

—

Inspect/repair circuits 264 and 265 for short to ground
or poor connections.
Was a problem found?

—

Go to Step 8

Go to Step 7

Replace PCM.
Is the replacement complete?

—

Go to Step 8

—

After the repair is complete, use the scan tool to
select “DTC,” then “Clear Info” function.

Select “Specific DTC” and enter DTC “P0748.”

Ensure the following conditions are met:

• The PCS duty cycle is not at its electrical high or

low limit (short cleared).

—

Repair veri-

fied, exit DTC

table.

Content .. 70 71 72 73 ..