Hummer H1 (2002+). Instruction - page 68

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Transmission/Transfer Case 5-71

®

05745159

3

1.

Turn the ignition OFF.

2.

Disconnect the OSS Sensor connector from the
OSS Sensor.

3.

Connect a J– 39200 DVOM on AC Voltage scale
between terminals A and B at the OSS Sensor.

4.

Start the engine, and place the transmission in D3
range.

5.

Slowly increase the wheel speed.

Is the voltage greater than the specified value?

Greater than

0.5 volts at

above 10 mph.

Go to Step 4

Go to Step 18

4

1.

Reconnect the OSS Sensor connector to the OSS
Sensor.

2.

Disconnect the VSS Buffer harness from the VSS
Buffer.

3.

Measure the voltage between terminals 7 and 12 of
the Buffer Harness Connector. Use the J– 39200
DVOM.

4.

Start the engine, and place the transmission in D3.

5.

With the wheels turning, slowly accelerate to 2000
RPM.

Is the voltage greater than the specified value?

0.5 volts AC

Go to Step 7

Go to Step 5

5

Inspect circuits 821 and 822 for an open. Refer to Elec-
trical Diagnosis, Section 8.
Did you find a problem?

__

Go to Step 16

Go to Step 6

6

Inspect circuits 821 and 822 for a short together or a
short to ground. Refer to Electrical Diagnosis, Section 8.
Did you find a problem?

__

Go to Step 16

__

7

1.

Turn the ignition to the OFF position.

2.

Measure the voltage between terminal 9 of the VSS
Buffer connector, and a good ground with the J–
39200 DVOM on DC volts.

3.

Turn the ignition ON.

Is the voltage greater than the specified valve?

10.5 volts DC

Go to Step 9

Go to Step 8

8

Inspect the ignition feed circuit 39 for an open.
Did you find a problem?

__

Go to Step 21

__

9

With the key to the ON position, measure the voltage
between terminals 8 and 9 of the VSS Buffer connector.
Is the voltage greater than the specified valve?

10.5 volts DC

Go to Step 11

Go to Step 10

10

Inspect the VSS Buffer Module ground circuit 451 for
an open.
Was the problem found and corrected?

__

Go to Step 21

__

DTC P0722 Output Speed Sensor Low Input (Cont’d)

Step

Action

Value

Yes

No

5-72

Transmission/Transfer Case

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®

11

With the connector off of the VSS Buffer Module and
the key to the ON position, measure the voltage between
terminal 13 of the VSS Buffer Harness Connector and a
good ground.
Is the voltage within the specified value?

4.8-5.2 volts
DC

Go to Step 15

Go to Step 12

12

Is the voltage in Step 12 greater than the specified
value?

5.2 volts DC

Go to Step 14

Go to Step 13

13

Inspect circuit 437 for an open or short to ground.
Did you find a problem?

__

Go to Step 21

Go to Step 17

14

Inspect circuit 437 for a short to power.
Did you find a problem?

__

Go to Step 21

Go to Step 17

15

1.

Reconnect the VSS Buffer Harness connector to the
VSS Buffer Module.

2.

With the DVOM set on DC volts and on a good
ground, back probe terminal 13 of the VSS Buffer
Module.

3.

Start the engine, and place the transmission in D3.

4.

With the wheels turning, slowly accelerate the
engine to 2000 RPM.

Is the voltage within the specified values?

1.5-3.5 volts
DC

Go to Step 17

Go to Step 19

16

Repair circuits 821 and 822. Refer to Repair Procedures,
Section 8.
Did you correct the problem?

Go to Step 21

17

Inspect the PCM for faulty or intermittent connections.
Did you find a problem?

Go to Step 21

Go to Step 20

18

Replace the OSS Sensor.
Is the replacement complete?

Go to Step 21

19

Replace the VSS Buffer Module.
Is the replacement complete?

Go to Step 21

20

Replace the PCM.
Is the replacement complete?

Go to Step 21

21

In order to verify your repair, perform the following pro-
cedure:
1.

Select DTC.

2.

Select Clear Info.

3.

Operate the vehicle under the following conditions:

• Drive the vehicle under steady acceleration.

• The PCM must see an output speed of greater

than 500 RPM for 1 second.

4.

Select Specific DTC. Enter DTC P0722.

Has the test run and passed?

System OK

Begin the

Diagnosis

again. Go to

Step 1

DTC P0722 Output Speed Sensor Low Input (Cont’d)

Step

Action

Value

Yes

No

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Transmission/Transfer Case 5-73

®

05745159

DTC P0723 Output Speed Sensor Intermittent

Circuit Description

The speed sensor circuit consists of a magnetic induction type
sensor, which is the Output Shaft Speed (OSS) Sensor, a Vehi-
cle Speed Sensor (VSS) Buffer Module, and wiring. Gear teeth
pressed onto the output shaft carrier assembly induce an alter-
nating voltage into the sensor. This signal transmits to the VSS
Buffer Module. The VSS Buffer Module compensates for vari-
ous final drive ratios. The VSS Buffer Module also converts
the alternating current (AC) OSS signal into a 40 pulse per rev-
olution (PPR) 5 volt DC square wave form signal on circuit
437 to indicate transmission output speed.

If the PCM detects an unrealistically large change in the Out-
put Shaft Speed (OSS) Sensor reading, then DTC P0723 sets.
DTC P0723 is a type A DTC.

Conditions for Setting the DTC

• No 4WD Low DTC P1875.

• No TFP Val. Position Sw. assembly change for greater

than 7 seconds.

• The engine must be running more than 475 RPM for at

least 7 second.

• The OSS RPM decrease is greater than 1000 RPM while

in a Drive gear for at least 4 seconds.

• The PCM sets the Malfunction Indicator Lamp (MIL).

Action Taken When the DTC Sets

• The PCM defaults to maximum line pressure.

• The PCM freezes shift adapts.

• The PCM defaults to the calculated output speed value

using the ISS Sensor values.

FUSE

3A

20A

EXTERIOR

HOT IN
RUN AND START

TWISTED

PAIR

A/T OUTPUT
SPEED SENSOR
SIGNAL (VSS)

BUFFERED

VSS

SIGNAL

POWERTRAIN

CONTROL

MODULE

(PCM)

VEHICLE

SPEED

SENSOR

(VSS)

A

B

A

B

13

7

C33

676 PP

679 LG

VEHICLE SPEED
SENSOR SIGNAL

IGNITION

POSITIVE
VOLTAGE

9

8

G2

570 BK

239 PK

C29-A3

C29-A6

565 BR

223 DB

14

4

VSS

SIGNAL

OUTPUT

BUFFERED

SPEED

SENSOR

SIGNAL

C3-P9

353 YL

11

C1-18

SPEEDO

VEHICLE
SPEED
SENSOR
BUFFER
(DRAC)

GROUND

SPEEDO

SIGNAL

9-S12-068

5-74

Transmission/Transfer Case

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®

Conditions for Clearing the DTC

1.

The PCM tuns OFF the MIL after three consecutive igni-
tion cycles without a failure reported.

2.

A scan tool can clear the DTC from the PCM history. The
PCM clears the DTC from the PCM history if the vehicle
completes 40 warm-up cycles without a failure reported.

3.

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

Diagnostic Aids

Inspect the wiring for poor electrical connections at the
PCM. Inspect the wiring for poor electrical connections at
the transmission 20-way connector. Look for the following
problems:

• A bent terminal

• A backed out terminal

• A damaged terminal

• Poor terminal tension

• A chafed wire

• A broken wire inside the insulation

It may be necessary to drive the vehicle.

When diagnosing for an intermittent short or open, mas-
sage the wiring harness while watching the test equipment
for a change.

Test Description

The numbers below refer to the numbers on the diagnostic ta-
ble.

2. This step verifies the fault condition.

4. This step verifies the OSS Sensor and circuit output to the

VSS Buffer Module.

7. This step tests the voltage supply to the VSS Buffer

Module.

9. This step tests the integrity of the ground circuit.

DTC P0723 Output Speed Sensor Intermittent

Step

Action

Value

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) Sys-
tem Check Performed?

Go to Step 2

Go to Power-
train OBD
System Check

2

1.

Install the scan tool (Tech 1).

2.

With the engine OFF, turn the ignition switch to the
RUN position.

Important

: Before clearing the DTCs, use the scan tool

in order to record the Freeze Frame and Failure Records
for reference. The Clear Info function will erase the
data.
3.

Record the DTC Freeze Frame and Failure Records
and DTCs.

4.

Raise and support the drive wheels.

5.

Start the engine and place the transmission in D3
range.

6.

With the Drive wheels rotating, slowly accelerate to
2000 RPM and hold.

Does the Transmission OSS drop or fluctuate more than
the specified value?

1000 RPM

Go to Step 3

No fault veri-
fied at this
time. Go to
Diagnostic
Aids

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