Hummer H1 (2006+). Manual - part 128

OBD-356

On-Board Diagnostics

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Action Taken When the DTC Sets

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

• When in a forward range, the transmission will fail to another forward range, unless the transmission is compromised by

over speeding or direction change, then the transmission will shift to NEUTRAL while diagnostic response is active.

•

If the shift selector is moved from a forward range to NEUTRAL or from a forward range to REVERSE, the transmission

will shift to NEUTRAL.

• If the shift selector is moved to REVERSE, the transmission will shift to REVERSE if it is not compromised by over

speeding or a direction change. If compromised, the transmission will shift to NEUTRAL.

• DTC P0870 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.

• When a P0870 and 0872 are set in combination, this may indicate a short to ground is present at the pressure switch cir-

cuit.

• This DTC can be set by a loss of prime.

• This DTC may indicate that E solenoid is mechanically defective.

Step

Action

Value(s)

Yes

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to

Diagnostic

System Check

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

Measure the line pressure.

Is the pressure within the specified value?

Go to Step 4

Go to

Symptoms

Automatic

Transmission

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On-Board Diagnostics OBD-357

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.

Start the engine.

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

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

Go to

Diagnostic Aids

Go to Step 5

Turn the ignition OFF.

Disconnect C79 at the TCM.

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

Connect C79 terminal 3 to a known good ground.

Turn ON the ignition, with the engine OFF.

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

Go to Step 6

Go to Step 12

Turn the ignition OFF.

Connect the C79 to the TCM.

Disconnect the transmission 20-way connector C34.

Turn the ignition ON. Additional DTCs might be set.

Connect C34 terminal E to a known good ground.

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

Go to Step 7

Go to Step 11

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

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

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

Go to Step 8

Go to Step 10

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

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

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

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

Go to Diagnos-

tic Aids

Go to Step 9

Replace the faulty PSM.

Did you complete the replacement?

Go to Step 13

Replace the AT internal wiring harness.

Did you complete the replacement?

Go to Step 13

Repair the wiring harness circuit 771 (WH) for an open or short.

Did you complete the repair?

Go to Step 13

Step

Action

Value(s)

Yes

OBD-358

On-Board Diagnostics

_____________________________________________

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

Perform the following procedure in order to verify the repair:

Clear the DTC.

Start the engine.

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

Select Specific DTC.

Enter DTC P0870.

Has test run and passed?

System OK

Go to Step 1

Step

Action

Value(s)

Yes

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On-Board Diagnostics OBD-359

5745804

DTC P0871 Transmission Pressure Switch Solenoid E Circuit Stuck Open (Figure OBD-93)

Figure OBD-93: Transmission Pressure Switch Solenoid E Circuit

Circuit Description

The pressure switch manifold (PSM) is a multiple-switch assembly made up of three normally open (N/O) and one normally closed
(N/C) pressure switches. The E pressure switch monitors E shift valve positioning and relays it to the transmission control module
(TCM). When E pressure switch is in the open state, E shift valve should be in the unstroked position.

DTC P0871 is a type A DTC.

Conditions for Setting the DTC

DTC P0871 sets when E solenoid is commanded ON and pressure switch E status remains OFF for 5 seconds, depending on fluid
temperature.

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