Hummer H1 (2002+). Instruction - page 81

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Transmission/Transfer Case 5-123

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05745159

Action Taken When The DTC Sets

• Assume “Low” state when stuck “off' and “High” state

when stuck ”on”.

• Freeze shift adapts from being updated.

• The PCM will illuminate the warning lamp.

Conditions For Clearing DTC

• The PCM will turn off the warning lamp after three con-

secutive ignition cycles without a failure reported.

• The DTC can be cleared using the scan tool. The DTC

will be cleared when the vehicle has achieved 40 warm-
up cycles without a failure reported.

• 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.

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, move or massage the wiring harness
while observing test equipment for a 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.

2. This test checks for voltage input to the 4WD indica-

tor assembly.

3. This test checks for voltage input to the selector quad-

rant switch through the 4WD indicator assembly.

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DTC P1875 4WD Low Switch Fault

Step

Action

Value

Yes

No

1

1.

Connect scan tool.

NOTE: Important:

Before clearing DTC(s) use the

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

2.

Turn ignition “on”.

3.

Record and clear DTC Freeze Frame/Failure
Records and DTCs.

4.

While observing scan tool shift transfer case into
4WD Hi and then 4WD Lo.

Does scan tool 4WD Lo Switch read “NO” when in
4WD Hl and “YES” when in 4WD Lo?

Problem may

be intermit-

tent. Refer to

Diagnostic

Aids.

2

1.

Turn ignition off.

2.

Disconnect transfer case switch harness connector.

3.

Turn the ignition on.

4.

Check terminal “B” on engine side of wiring har-
ness for voltage.

Is B+ voltage available at terminal “B”?

Go to Step 3

Go to Step 6

3

1.

Ground switch ground wire to a known good
ground.

2.

Observe scan tool 4WD Lo Sw data.

Does scan tool 4WD Lo indicate “YES” when the circuit
is grounded and “NO” when it is not grounded?

Go to Step 4

Go to Step 8

4

Check terminal at transfer case switch.

Was problem found and corrected?

Go to Step 8

Go to Step 5

5

Replace transfer case 4WD Lo Switch.

Was the 4WD Lo Switch replaced?

Go to Step 8

6

Check switch harness for open.

Was problem found and corrected?

Go to Step 8

Go to Step 7

7

1.

Replace the PCM.

Was the PCM replaced?

Go to Step 8

8

1.

After the repair is complete select scan tool “Clear
Info” function and operate the vehicle under the fol-
lowing conditions:

• Start the engine and drive the vehicle. 4th gear

and TCC engagement must occur both in high and
low ranges. The PCM must see a valid gear range
in both transfer case ranges.

2.

Review the scan tool “DTC Info”.

Repair veri-

fied, exit

DTC table.

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Transmission/Transfer Case 5-125

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05745159

Electrical/Garage Shift Test

Perform this test before a road test in order to make sure that
electronic control inputs are connected and operating. If you do
not check the inputs before operating the transmission, you
could misdiagnose a simple electrical condition as a major
transmission condition.

A scan tool provides valuable information. Use the scan tool
on the transmission for accurate diagnosis.

1.

Move the gear selector to Park and set the parking brake.

2.

Connect the scan tool to the DLC connector.

3.

Start the Engine

4.

Verify that the following signals are present on the scan
tool:

• Transmission Input (shaft) Speed Sensor (A/T ISS)

• Transmission Output(shaft) Speed Sensor (VSS)

• Automatic Transmission Fluid Pressure Manual Valve

Position Switch (TFP val.)

• Vehicle speed

• Current Gear

• Reference Transmission Pressure Control Solenoid Am-

perage (Ref Current)

• Actual Transmission Pressure Control Solenoid Amper-

age (ACT CURRENT)

• Engine Coolant Temperature (ECT)

• Automatic Transmission Fluid Temperature Signal

(TFT)

• APP angle

• TCC duty cycle (TCC DC)

• System Voltage

• TCC Brake Switch

5.

Monitor the TCC BRAKE signal with the scan tool while
tapping the brake pedal with your foot. The brake switch
signal should be:

• Open - when the brake pedal is released

• Closed - when the brake pedal is depressed

6.

Monitor the Automatic Transmission Fluid Pressure
Manual Valve Position Switch signal by moving the gear
selector through all of the ranges. Verify that the FRP
Switch state matches the gear range which is indicated on
the instrument panel or on the console. Gear selections
should be immediate and not harsh.

7.

Move the gear selector to Neutral and monitor the APP
angle while increasing and decreasing engine RPM with
the accelerator pedal. The Throttle angle should increase
with the engine RPM.

Torque Converter Clutch Diagnosis

The Torque Converter Clutch (TCC) is applied by fluid pres-
sure, which is controlled by a PWM solenoid valve. This sole-
noid valve is located inside of the automatic transmission

assembly. The solenoid valve energizes or de-energizes by
making or breaking an electrical circuit through a combination
of switches and sensors.

Torque Converter Stator

The torque converter stator roller clutch can have two different
malfunctions.

• The stator assembly freewheels in both directions

• The stator assembly remains locked up at all times

Poor Acceleration at Low Speed

If the stator is freewheeling at all times, the car tends to have
poor acceleration from a standstill. At speeds above 50 -55 km/
h (30-35 mph), the car may act normally. For poor acceleration
you should first determine that the exhaust system is not
blocked, and the transmission is in First gear when starting out.

If the engine freely accelerates to high RPM in Neutral, you
can assume that the engine and the exhaust system are normal.
Check for poor performance in Drive and Reverse to help de-
termine if the stator is freewheeling at all times.

Poor Acceleration at High Speed

If the stator is locked up at all times, performance is normal
when accelerating from a standstill. Engine RPM and car speed
are limited or restricted at high speeds. Visual examination of
the converter may reveal a blue color from overheating.

If the converter has been removed, you can check the stator
roller clutch by inserting a finger into the splined inner race of
the roller clutch and trying to turn the race in both directions.
You should be able to freely turn the inner race clockwise, but
you should have difficulty in moving the inner race counter-
clockwise or you may be unable to move the race at all.

Noise

Important:

Do not confuse this noise with pump whine noise,

which is usually noticeable in Park, Neutral, and all other gear
ranges. Pump whine with vary with line pressure.

You may notice a torque converter whine when the vehicle is
stopped and the transmission is in Drive or Reverse. This noise
will increase as you increase the engine RPM. The noise will
stop when the vehicle is moving or when you apply the torque
converter clutch, because both halves of the converter are turn-
ing at the same speed.

Perform a stall test to make sure the noise is actually coming
from the converter:

1.

Place your foot on the brake

2.

Put the gear selector in Drive.

NOTE:

You may damage the transmission if you depress the

accelerator for more than six seconds.

3.

Depress the accelerator to approximately 1200 RPM for
no more than six seconds.

A torque converter noise will increase under this load.

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Torque Converter Evaluation and Diagnosis

Replace the torque converter under any of the following condi-
tions:

• External leaks appear in the hub weld area.

• The converter hub is scored or damaged.

• The converter pilot is broken, damaged, or fits poorly

into the crankshaft.

• You discover steel particles after flushing the cooler and

cooler lines.

• The pump is damaged, or you discover steel particles in

the converter.

• The vehicle has TCC shudder and/or no TCC apply. Re-

place the torque converter only after all hydraulic and
electrical diagnoses have been made. The converter
clutch material may be glazed

• The converter has an imbalance which cannot be cor-

rected. Refer to Flywheel/Torque Converter Vibration
Test.

• The converter is contaminated with engine coolant

which contains antifreeze.

• An internal failure occurs in the stator roller clutch.

• You notice excessive end play.

• Overheating produces heavy debris in the clutch.

• You discover steel particles or clutch lining material in

the fluid filter or on the magnet, when not internal parts
in the unit are worn or damaged. This condition indi-
cates that lining material came from the converter.

Do Not Replace the Torque Converter

Do not replace the torque converter if you discover any of the
following symptoms:

• The oil has an oder or the fluid is discolored, even

though metal or clutch facing particles are not present.

• The threads in one or more of the converter bolt holes

are damaged. Correct the condition with a new J-nut.

• Transmission failure did not display evidence of dam-

aged or worn internal parts, steel particles or clutch plate
lining material in the unit and inside the fluid filter.

Torque Converter Clutch Shudder

The key to diagnosing Torque Converter Clutch shudder is to
note when it happens and under what conditions.

TCC shudder which is caused by the transmission should only
occur during the apply or the release of the converter clutch.
Shudder should never occur after the TCC plate is fully ap-
plied.

If the shudder occurs while the TCC is applying, the problem
can be within the transmission or the torque converter. Some-
thing is causing one of the following conditions to occur:

• Something is not allowing the clutch to become fully

engaged.

• Something is not allowing the clutch to release.

• The clutch is releasing and applying at the same time.

One of the following conditions may be causing the problem to
occur:

• Leaking turbine shaft seals

• A restricted release orifice

• A distorted clutch or housing surface due to long con-

verter bolts

• Defective friction material on the TCC plate

If Shudder Occurs After TCC has Applied

If shudder occurs after the TCC has applied, most of the time
there is nothing wrong with the transmission!

As mentioned above, the TCC is not likely to slip after the
TCC has been applied. Engine problems may go unnoticed un-
der light throttle and load, but they may become noticeable af-
ter the TCC apply when going up a hill or accelerating. This is
due to the mechanical coupling between the engine and the
transmission.

Once TCC is applied, there is no torque converter assistance.
Engine or driveline vibrations could be unnoticeable before
TCC engagement.

Flywheel/Torque Converter Vibration Test

1.

Start the engine.

2.

With the engine at idle speed and the transmission in Park
or Neutral, observe the vibration.

3.

Turn the key off.

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