Hummer H1 (2006+). Manual — part 127

OBD-352

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 and shifting is completed, the transmission will fail to another forward range, unless the trans-

mission is compromised by over speeding or direction change, then the transmission will shift to NEUTRAL.

• When in a forward range and the shift is in process, the transmission will return to a previous range, except for 1-2 shifts

and 2-1 shifts which will be completed.

• When in NEUTRAL or REVERSE, the transmission will fail to NEUTRAL.

• While diagnostic response is active, the shift selector is moved from a forward range to NEUTRAL or from a forward

range to REVERSE, then the transmission will shift to NEUTRAL.

• DTC P0848 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.

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

•

When a P0848 and P0846 are set in combination, this may indicate an open circuit is present at the pressure switch circuit

or the shift valve is stuck in the unstroked position.

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

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

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On-Board Diagnostics OBD-353

5745804

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. D status.

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

Go to

Diagnostic Aids

Go to Step 5

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 2 to a known good ground.

5.

Turn ON the ignition, with the engine OFF.

Does the scan tool indicate TFP SW. D 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 F to a known good ground.

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

Go to Step 7

Go to Step 14

7

1.

Connect the transmission C34.

2.

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

3.

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

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

Go to Step 8

Go to Step 13

8

1.

Remove the PSM from the control valve body and leave the
internal harness connected. Refer to Pressure Switch Mani-
fold Replacement.

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 pressure
switch D membrane.

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

Go to Step 9

Go to Step 12

9

Remove the control valve body and inspect for a stuck or sticking
D shift valve.

Was the D shift valve stuck or sticking?

Go to Step 11

Go to Step 10

10

Replace the D shift solenoid and install the control valve body.
Did you complete the replacement and install the control valve
body?

Go to Step 16

Step

Action

Value(s)

Yes

No

OBD-354

On-Board Diagnostics

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11

Clean and/or polish the sticking valve to restore free movement,
or replace the control valve body assembly.

Did you restore free movement or replace the valve body?

Go to Step 16

12

Replace the faulty PSM.

Did you complete the replacement?

Go to Step 16

13

Replace the faulty AT internal wiring harness.

Did you complete the replacement?

Go to Step 16

14

Repair the wiring harness circuit 770 (PK) for an open or short.

Did you complete the repair?

Go to Step 16

15

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 16

16

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. D status.

4.

Select Specific DTC.

5.

Enter DTC P0847.

Has the test run and passed?

System OK

Go to Step 1

Step

Action

Value(s)

Yes

No

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On-Board Diagnostics OBD-355

5745804

DTC P0870 Transmission Pressure Switch Solenoid E Circuit (Figure OBD-92)

Figure OBD-92: 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 P0870 is a type A DTC.

Conditions for Setting the DTC

DTC P0870 sets during steady state operation when pressure switch E indicates ON for 20 milliseconds after E solenoid has been
commanded OFF.