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.
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