Hummer H1 (2006+). Manual - part 155

OBD-464

On-Board Diagnostics

_____________________________________________

NOTE: The fuel level must be between 25-50 percent in order to
perform this diagnostic procedure. If the fuel level is not within
this range, misdiagnosis will occur.

Turn ON the ignition, with the engine OFF.

Command the fuel pump relay ON and OFF with a scan tool.

Does the fuel pump relay click?

Go to Step 9

Go to Step 4145

Remove the fuel pump relay from the underhood electrical
center.

Probe the ground circuit of the fuel pump relay with a test
lamp that is connected to battery voltage.

Does the test lamp illuminate?

Go to Step 5

Go to Step 25

Probe the fuel pump relay control circuit with a test lamp
that is connected to a good ground.

Command the fuel pump relay ON and OFF with a scan tool.

Does the test lamp turn ON and OFF?

Go to Step 22

Go to Step 6

Does the test lamp remain illuminated?

Go to Step 7

Go to Step 8

Test the fuel pump relay control circuit for a short to voltage.

Did you find and correct the condition?

Go to Step 31

Go to Step 24

Test the fuel pump relay control circuit for an open or a short to
ground.

Did you find and correct the condition?

Go to Step 31

Go to Step 24

Command the fuel transfer pump ON with a scan tool.

Does the fuel transfer pump operate?

Go to Step 17

Go to Step 10

Remove the fuel pump relay from the underhood electrical
center.

Turn ON the ignition, with the engine OFF.

Probe the battery voltage circuit of the fuel pump relay with
a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 11

Go to Step 12

Connect a fused jumper wire between the fuel pump relay battery
voltage circuit and the fuel pump supply voltage circuit.

Does the fuel pump operate?

Go to Step 22

Go to Step 15

Is the battery positive voltage fuse open?

Go to Step 13

Go to Step 27

Test the battery voltage circuit of the fuel pump relay for a short
to ground.

Did you find and correct the condition?

Go to Step 31

Go to Step 14

Test the fuel pump supply voltage circuit for a short to ground.

Did you find and correct the condition?

Go to Step 31

Go to Step 23

Test the fuel transfer pump supply voltage circuit for an open.

Did you find and correct the condition?

Go to Step 31

Go to Step 16

Step

Action

Value(s)

Yes

_____________________________________________

On-Board Diagnostics OBD-465

5745804

Probe the ground circuit of the fuel transfer pump with a test
lamp that is connected to battery voltage.

Does the test lamp illuminate?

Go to Step 23

Go to Step 26

Observe the fuel level sensor rear tank voltage parameter with a
scan tool.

Is the voltage less than the specified value?

2.2 Volts

Go to Step 19

Go to Step 18

Add the specified amount of fuel to the rear fuel tank.

Did you complete the action?

19 L (5

gal)

Go to Step 19

Connect a fused jumper wire between the fuel pump relay
battery voltage circuit and the fuel pump voltage supply cir-
cuit.

Observe the Fuel Level sensor voltage parameter with a scan
tool.

Does the rear fuel level sensor voltage parameter decrease as the
fuel pump is operating?

Go to Step 20

Go to Step 21

Disconnect the outlet hose from the fuel transfer pump.

Connect a section of rubber hose with a clamp to the outlet
port of the transfer pump.

Insert the other end of the rubber hose into a container to
measure more than 4 liters (1.06 gallons).

Operate the transfer pump with a scan tool for a total of 120
seconds.

Measure the fuel in the container.

Does the fuel volume measure more than the specified value?

2.6 L (0.70

gal)

Go to Intermit-

tent Conditions

Go to Step 21

Inspect for the following conditions:

• A restriction in the fuel lines between the front and rear

fuel tanks

• The rear fuel sender for a restriction

Did you find and correct the condition?

Go to Step 31

Go to Step 29

Inspect for poor connections at the harness connector of the fuel
pump relay.

Did you find and correct the condition?

Go to Step 31

Go to Step 28

Inspect for poor connections at the harness connector of the fuel
transfer pump.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

Inspect for poor connections at the harness connector of the en-
gine control module (ECM).

Did you find and correct the condition?

Go to Step 31

Go to Step 30

Repair the open ground circuit of the fuel pump relay.

Did you complete the repair?

Go to Step 31

Repair the open ground circuit of the fuel transfer pump.

Did you complete the repair?

Go to Step 31

Step

Action

Value(s)

Yes

OBD-466

On-Board Diagnostics

_____________________________________________

Repair the open battery voltage circuit of the fuel pump relay.

Did you complete the repair?

Go to Step 31

Replace the faulty fuel pump relay.

Did you complete the replacement?

Go to Step 31

Replace the faulty fuel transfer pump.

Did you complete the replacement?

Go to Step 31

Replace the faulty ECM.

Did you complete the replacement?

Go to Step 31

Clear the DTCs with a scan tool.

Turn OFF the ignition for 30 seconds.

Start the engine.

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 Diagnos-

tic Aids

Go to Step 32

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnos-

tic Trouble

Code (DTC)

List

System OK

Step

Action

Value(s)

Yes

_____________________________________________

On-Board Diagnostics OBD-467

5745804

DTC P2771 Four Wheel Drive (4WD) Low Switch Circuit

Circuit Description

The 4WD low signal circuit is used to notify the transmission control module (TCM) that the vehicle is in 4WD low range.

DTC P2771 is a type B DTC.

Conditions for Setting the DTC

DTC P2771 sets when one of the following conditions occur:

• The transfer case switch indicates high range, and the calculated range is low range for 5 seconds or greater.

• The transfer case switch indicates low range, and the calculated range is high range for 5 seconds or greater.

Action Taken When the DTC Sets

• The TCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions

for Setting the DTC are met.

• DTC 2771 will be stored in TCM history.

• The TCM inhibits torque converter clutch (TCC) engagement.

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.

• Inspect for any transmission DTCs that may have set again.

Step

Action

Value(s)

Yes

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnos-

tic System

Check

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.

Using the scan tool, monitor 4WD Low status and select 4HI
followed by 4LO with the transfer case selector.

Does the scan tool indicate 4WD low status as NO when 4HI is
selected, and YES when 4LO is selected?

Go to Diagnos-

tic Aids

Go to Step 3

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