Hummer H1 (2006+). Manual - part 132

OBD-372

On-Board Diagnostics

_____________________________________________

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. 

•    This DTC could indicate a hydraulic leak path exhausting pressure from the reverse pressure switch. 

•    An inactive DTC P0875 set in combination with DTC P0872 often indicates that an internal PNP switch failure occurred 

on a previous drive cycle. If this combination returns after clearing the DTCs, replacement of the PNP switch may be 
necessary.

•

The intent of this code is to detect discrepancies between the range selected at the PNP and the actual position of the man-

ual selector valve. 

Step

Action

Value(s)

Yes

No

    1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to           

Diagnostic

System 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         

Transmission

Fluid Checking 

Procedure

    3

Measure the line pressure. 

Is the pressure within the specified value?

Go to Step 4

Go to        

Symptoms

Automatic

Transmission

    4

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.

Start the engine.

6.

Using the scan tool, monitor TFP SW. R status.

Does the scan tool indicate TFP SW. R status is ON?

Go to     

Diagnostic Aids

Go to Step 5

_____________________________________________

 On-Board Diagnostics  OBD-373

5745804

    5

1.

Turn the ignition OFF.

2.

Disconnect C79 at the TCM.

3.

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

4.

Connect C79 terminal 4 to a known good ground.

5.

Turn ON the ignition, with the engine OFF.

Does the scan tool indicate TFP SW. R status is ON when
grounded and OFF when open?

Go to Step 6

Go to Step 12

    6

1.

Turn the ignition OFF.

2.

Connect the C79 to the TCM.

3.

Disconnect the transmission 20-way connector C34.

4.

Turn the ignition ON. Additional DTCs might be set.

5.

Connect C34 terminal K to a known good ground.

Does the scan tool indicate TFP SW. R status is ON when
grounded and OFF when open?

Go to Step 7 

Go to Step 11

    7

1.

Remove the oil pan. Refer to Transmission Oil Pan Replace-
ment .

2.

Disconnect the AT internal wiring harness from the PSM and 
ground terminal D.

Does the scan tool indicate TFP SW. R status is ON when
grounded and OFF when open?

Go to Step 8 

Go to Step 10

    8

1.

Remove the PSM from the control valve body and leave the 
internal harness connected. 

2.

Provide a ground connection for the PSM to either the con-
trol valve body or the transmission main case.

3.

Using the eraser end of a pencil, push gently on the reverse 
pressure switch membrane.

Does the scan tool indicate TFP SW. R status is ON when
grounded and OFF when open?

Go to Diagnos-

tic Aids

Go to Step 9

    9

Replace the faulty PSM. 

Did you complete the replacement?

Go to Step 13 

    10

Replace the AT internal wiring harness. 

Did you complete the replacement?

Go to Step 13 

    11

Repair the wiring harness circuit 772 (DG) for an open or short. 

Did you complete the repair?

Go to Step 13 

    12

NOTE: In most cases, the TCM is not at fault. Investigate thor-
oughly before replacing the TCM.

Replace the faulty TCM. 

Did you complete the replacement?

Go to Step 13 

Step

Action

Value(s)

Yes

No

OBD-374

On-Board Diagnostics

_____________________________________________

    13

Perform the following procedure in order to verify the repair:

1.

Clear the DTC.

2.

Start the engine.

3.

Using the scan tool, monitor TFP SW. Reverse status.

4.

Select Specific DTC.

5.

Enter DTC P0875.

Has test run and passed?

System OK

Go to Step 1

Step

Action

Value(s)

Yes

No

_____________________________________________

 On-Board Diagnostics  OBD-375

5745804

DTC P0876 Transmission Pressure Switch Reverse Circuit Stuck Open (Figure OBD-97)

Figure OBD-97:   Transmission Pressure Switch Reverse Circuit

Circuit Description

The pressure switch manifold (PSM) is a multiple-switch assembly made up of three normally open (N/O) pressure switches and
one normally closed (N/C) pressure switch for reverse pressure. Fluid pressure is supplied to the reverse pressure switch when the
manual selector valve is in any position, except REVERSE. When the manual selector valve is moved to REVERSE, pressure to
the reverse pressure switch is cut off causing the switch to close.

DTC P0876 is a type B DTC.

Conditions for Setting the DTC

DTC P0876 sets when a forward range has been selected and the reverse pressure switch remains in the mechanically open/electri-
cally off position for more than 1 second.