Hummer H1 (2006+). Manual - part 119

OBD-320

On-Board Diagnostics

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DTC P0802 Transmission Control Module (TCM) MIL Request Circuit (Figure OBD-83)

Figure OBD-83:   Transmission Control Module (TCM) MIL Request Circuit

Circuit Description

The transmission control module (TCM) malfunction indicator lamp (MIL) request circuit signals the engine control module
(ECM) that the TCM is requesting MIL illumination.

Conditions for Setting the DTC

The ECM is detecting an improper voltage level on the TCM MIL request circuit within 7 seconds of the key ON.

Action Taken When the DTC Sets 

• The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diag-

nostic runs and fails. 

• The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the

control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecu-
tive ignition cycle, the control module records the operating conditions at the time of the failure. The control module 
writes the operating conditions to the Freeze Frame and updates the Failure Records. 

Conditions for Clearing the MIL/DTC 

• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic 

runs and does not fail. 

• A current DTC, Last Test Failed, clears when the diagnostic runs and passes. 

• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related 

diagnostic.

• Clear the MIL and the DTC with a scan tool. 

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 On-Board Diagnostics  OBD-321

5745804

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

1.

Observe the Freeze Frame/Failure Records data for this 
DTC.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine.

4.

Operate the vehicle within the Conditions for Running the 
DTC as specified in the supporting text or as close to the 
Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

Go to Step 3

Go to          

Intermittent

Conditions

    3

1.

Turn OFF the ignition.

2.

Disconnect the TCM C78.

3.

Connect a DVOM from the TCM malfunction indicator lamp 
(MIL) request circuit 661 (GN) at the TCM harness C78 to a 
good ground.

4.

Turn ON the ignition, with the engine OFF.

Does the voltage measure near the specified value?

B+

Go to Step 4 

Go to Step 5

    4

Test the TCM MIL request circuit 661 (GN) for a short to voltage
between C78 pin 25 and C76 pin 21. 

Did you find and correct the condition?

Go to Step 11

Go to Step 6

    5

Test the TCM MIL request circuit 661 (GN) for an open between
C78 pin 25 and C76 pin 21 and repair.

Did you find and correct the condition?

Go to Step 11 

Go to Step 6 

    6

1.

Leave the TCM disconnected.

2.

Connect a fused jumper wire from the TCM MIL request cir-
cuit 661 (GN) C78 pin 25 to a good ground.

3.

Clear the DTCs with a scan tool.

Does DTC P0700 set, but not DTC P0802?

Go to Step 7 

Go to Step 9

    7

Perform the following procedures:

• Check the battery and powers and grounds of the TCM for 

high resistance or corrosion. 

• Test the TCM connectors for a poor connection. 

Did you find and correct the condition?

Go to Step 11 

Go to Step 8

    8

Replace the faulty TCM. 

Did you complete the action?

Go to Step 11 

    9

Test the engine control module (ECM) connectors for a poor con-
nection.

Did you find and correct the condition?

Go to Step 11 

    10

Replace the faulty ECM. 

Did you complete the replacement?

Go to Step 11

OBD-322

On-Board Diagnostics

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    11

1.

Clear the DTCs with a scan tool.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine.

4.

Operate the vehicle within the Conditions for Running the 
DTC. You may also operate the vehicle within the conditions 
that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 2 

Go to Step 12 

    12

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to     

Diagnostic

Trouble Code 

(DTC) List 

System OK

Step

Action

Value(s)

Yes

No

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 On-Board Diagnostics  OBD-323

5745804

DTC P0840 Transmission Pressure Switch Solenoid C Circuit (Figure OBD-84)

Figure OBD-84:   Transmission Pressure Switch Solenoid C 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 C pressure switch monitors C shift valve positioning and relays it to the transmission control module
(TCM). When the C pressure switch is in the open state, the C shift valve should be in the unstroked position.

DTC P0840 is a type A DTC.

Conditions for Setting the DTC

DTC P0840 sets during steady state operation when pressure switch C indicates ON for 125 milliseconds after C solenoid has been
commanded OFF.