Hummer H1 (2006+). Manual - part 103

OBD-256

On-Board Diagnostics

_____________________________________________

Action Taken When the DTC Sets

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

• When failure occurs in a forward range and shifting is complete, the transmission remains in the current range. When failure

occurs while in a forward range and the shift is in process, the transmission returns to the previous range, except in post-
shift state, where the transmission will continue to the commanded range. When failure occurs in other conditions, the
transmission shifts to 1st, 3rd or 5th. While diagnostic response is active, if the shift selector is moved to NEUTRAL or
REVERSE or any other forward range, then the transmission will lock in NEUTRAL.

• DTC P0721 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.

• If the condition is intermittent, connect the scan tool and select the speed sensor indicated by the code. If the signal is erratic,

investigate and eliminate the following:

• Intermittent wiring connection

• Excessive vibration, such as driveline or engine torsionals

• Irregular sensor gap, such as a loose sensor, a loose tone wheel or a damaged tone wheel

• Inspect that the speed sensor wiring consists of twisted pairs at the rate of 12-16 twists per 300 mm (12 in). These twists

must extend the entire length of the wiring harness to within at least 50 mm (2 in) of the speed sensor connector.

Step

Action

Value(s)

Yes

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.

_____________________________________________

On-Board Diagnostics OBD-257

5745804

Install the scan tool.

Turn ON the ignition, with the engine OFF.

NOTE: Before clearing the DTC, use the scan tool in order to
record the Freeze Frame and Failure Records for reference. The
Clear Info function will erase the data.

Record the DTC Freeze Frame and Failure Records.

Clear the DTC.

Using the scan tool, observe ignition voltage.

Is the voltage within the specified range?

9-18 Volts

Go to Step 3

Go to DTC

P0562 for low

voltage or DTC

P0563 for high

voltage

Turn the ignition OFF.

Disconnect the C79 from the TCM.

Install the J 39700 breakout box and the J 43799 breakout
box adapter at the C79.

Using a DVOM, measure the resistance between connector
C79 pin 15 and 16.

Is the speed sensor resistance within the specified values?

2,600

ohms

[commat]

25°C

(77°F)

Go to Diagnos-

tic Aids

Go to Step 4

Disconnect the wiring harness from the turbine speed sensor.

Using a DVOM, measure the resistance between the speed
sensor terminals.

Is the speed sensor resistance within the specified values?

2,600

ohms

[commat]

25°C

(77°F)

Go to Step 5

Go to Step 6

Repair the engine wiring harness.

Did you complete the repair?

Go to Step 7

NOTE: Do not rotate the speed sensor in the retaining bracket.
Orientation is fixed, and if changed, may cause improper opera-
tion.

Replace the faulty output speed sensor.

Did you complete the replacement?

Go to Step 7

Go to Diagnos-

tic Aids

Perform the following procedure in order to verify the repair:

Clear the DTC.

Using the scan tool, monitor the turbine speed sensor opera-
tion.

Select Specific DTC.

Enter DTC P0721.

Has the test run and passed?

System OK

Go to Step 1

Step

Action

Value(s)

Yes

OBD-258

On-Board Diagnostics

_____________________________________________

DTC P0722 Output Speed Sensor Circuit No Signal (Figure OBD-72)

Figure OBD-72: Output Speed Sensor Circuit

Circuit Description

The speed sensors are variable reluctance devices that convert mechanical motion to an AC voltage. Each sensor consists of a wire
coil wrapped around a pole piece that is adjacent to a permanent magnet. These elements are contained in a housing that is mounted
adjacent to a rotating ferrous member. Two signal wires extend from one end of the housing and an exposed end of the pole piece
is at the opposite end of the housing. The permanent magnet produces lines of flux around the pole piece. As a ferrous object, such
as a gear tooth, approaches and passes through the gap at the end of the pole piece, an AC voltage pulse is induced in the wire coil.
The transmission control module (TCM) calculates the frequency of these AC pulses and converts it to a speed value. The AC volt-
age generated varies from 150 millivolt at low speed to 15 volts at high speed. The signal wires from the sensor are formed as
twisted pairs to cancel magnetically induced fields. The cable is also shielded to protect from voltage-related fields. Using two-
wire differential inputs at the TCM eliminates noise from other sources.

DTC P0722 is a type A DTC.

_____________________________________________

On-Board Diagnostics OBD-259

5745804

Conditions for Setting the DTC

DTC P0722 sets when the TCM detects one of the following conditions:

• An unrealistically large change in output speed

• An unrealistically low output speed

Action Taken When the DTC Sets

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

• When failure occurs in a forward range and shifting is complete, the transmission remains in the current range. When failure

• DTC P0722 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.

• If the condition is intermittent, connect the scan tool and select the speed sensor indicated by the code. If the signal is erratic,

investigate and eliminate the following:

• Intermittent wiring connection

• Excessive vibration, such as driveline or engine torsionals

• Irregular sensor gap, such as a loose sensor, a loose tone wheel or a damaged tone wheel

• Inspect that the speed sensor wiring consists of twisted pairs at the rate of 12-16 twists per 300 mm (12 in). These twists

must extend the entire length of the wiring harness to within at least 50 mm (2 in) of the speed sensor connector.

Step

Action

Value(s)

Yes

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.

6-1-05

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