Hummer H1 (2006+). Manual - part 105

OBD-264

On-Board Diagnostics

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DTC P0727 Engine Speed Circuit No Signal (Figure OBD-74)

Figure OBD-74:   Engine Speed 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 P0727 is a type B DTC.

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 On-Board Diagnostics  OBD-265

5745804

Conditions for Setting the DTC

DTC P0727 sets if engine speed is detected less than 61 RPM for 4 seconds.

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 P0727 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.

OBD-266

On-Board Diagnostics

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    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 P0727.

Has the test run and passed? 

System OK

Go to Step 1

Step

Action

Value(s)

Yes

No

_____________________________________________

 On-Board Diagnostics  OBD-267

5745804

DTC P0731 Incorrect First Gear Ratio

Circuit Description

The transmission control module (TCM) uses input from the turbine speed sensor and the output speed sensor to determine gear ra-
tios. The TCM then compares the known gear ratio to the calculated gear ratio for the current range.

DTC P0731 is a type A DTC.

Conditions for Setting the DTC

DTC P0731 sets when the calculated first range ratio, steady state, differs from the known first range ratio.

Action Taken When the DTC Sets 

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

•  The transmission defaults to 2nd or 5th range while diagnostic response is active. 

•    If the shift selector is moved to NEUTRAL, the transmission will shift to NEUTRAL. 

•   If the shift selector is moved to REVERSE, the transmission will either lock in NEUTRAL or shift to REVERSE, unless 

the transmission is compromised by over speeding or direction change. If this occurs, the transmission will lock in NEU-
TRAL.

•   DTC P0731 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 

•   Incorrect ratio codes typically indicate mechanical conditions with specific clutches, such as C1 or C5 for first range. 

•   Incorrect ratio code could indicate a hydraulically failed solenoid. Observe DTC information for the specific solenoid. 

•   Clutch test mode can be used to measure stall speed. 

•   You may have to drive the vehicle in order to experience a condition. 

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.

    2

Measure the transmission fluid level. Refer to Transmission Fluid
Checking Procedure.

Is the transmission fluid level correct?

Go to Step 3 

Go to Transmis-

sion Fluid 

Checking Proce-

dure