Hummer H1 (2006+). Manual — part 104

OBD-260

On-Board Diagnostics

_____________________________________________

2

1.

Install the scan tool.

2.

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.

3.

Record the DTC Freeze Frame and Failure Records.

4.

Clear the DTC.

5.

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

3

1.

Turn the ignition OFF.

2.

Disconnect the C79 from the TCM.

3.

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

4.

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

Is the speed sensor resistance within the specified values?

1,420-

2,140

ohms

Go to Diagnos-

tic Aids

Go to Step 4

4

1.

Disconnect the wiring harness from the turbine speed sensor.

2.

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

Is the speed sensor resistance within the specified values?

1,420-

2,140

ohms

Go to Step 5

Go to Step 6

5

Repair the engine wiring harness.

Did you complete the repair?

Go to Step 7

6

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

7

Perform the following procedure in order to verify the repair:

1.

Clear the DTC.

2.

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

3.

Select Specific DTC.

4.

Enter DTC P0721.

Has the test run and passed?

System OK

Go to Step 1

Step

Action

Value(s)

Yes

No

_____________________________________________

On-Board Diagnostics OBD-261

5745804

DTC P0726 Engine Speed Sensor Input Circuit Performance (Figure OBD-73)

Figure OBD-73: Engine Speed Sensor Input 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 P0726 is a type B DTC.

OBD-262

On-Board Diagnostics

_____________________________________________

Conditions for Setting the DTC

DTC P0726 sets when the TCM detects a large unrealistic engine speed or if excessive noise is present in the engine speed sensor
circuit.

Action Taken When the DTC Sets

• The TCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for

Setting the DTC are met.

• DTC P0726 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

No

1

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-263

5745804

2

1.

Install the scan tool.

2.

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.

3.

Record the DTC Freeze Frame and Failure Records.

4.

Clear the DTC.

5.

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

3

1.

Turn the ignition OFF.

2.

Disconnect the C79 from the TCM.

3.

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

4.

Using a DVOM, measure the resistance between connector
C79 pin 17 and 18.

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

4

1.

Disconnect the wiring harness from the turbine speed sensor.

2.

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

5

Repair the engine wiring harness.

Did you complete the repair?

Go to Step 7

6

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 transmission input speed sensor.

Did you complete the replacement?

Go to Step 7

Go to Diagnos-

tic Aids

7

Perform the following procedure in order to verify the repair:

1.

Clear the DTC.

2.

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

3.

Select Specific DTC.

4.

Enter DTC P0726.

Has the test run and passed?

System OK

Go to Step 1

Step

Action

Value(s)

Yes

No