Hummer H1 (2006+). Manual - part 135

OBD-384

On-Board Diagnostics

_____________________________________________

    6

Inspect for fuel contamination. 

Did you find and correct the condition?

Go to Step 17 

Go to Step 7 

    7

1.

Install the J 44638 Vacuum Gage on the fuel fitting located 
on the right side front of the engine.

2.

Start and run the engine at idle.

3.

Observe the vacuum gage while increasing RPM slowly to 
wide open throttle (WOT) in Park or Neutral.

Does the vacuum measure less than the specified value through
the entire RPM range?

5 inches

Go to Step 8

Go to Step 11

    8

1.

Start and idle the engine until the idle speed drops to 680 
RPM.

2.

Command the fuel pressure control to 160 MPa with a scan 
tool.

3.

Observe the Actual Fuel Rail Pressure parameter with a scan 
tool.

Is the Actual Fuel Rail Pressure parameter more than the speci-
fied value?

145 MPa

Go to Step 9

Go to Fuel   

System

Diagnosis

High Pressure 

Side

    9

NOTE: If the fuel temperature is near 121°C (250°F) during the
duplication of the complaint or in the Failure Records for this
DTC, inspect for a restriction in the fuel cooler air flow or the
fuel heater always ON. Refer to Fuel Heater Always On .

1.

Ensure that the J 44638 is still installed on the engine.

2.

Operate the vehicle within the conditions for which the cus-
tomer complaint occurs.

Does the vacuum measure less than the specified value through
the entire operating range?

12 inches

Go to 

Diagnostic Aids

Go to Step 11 

    10

1.

Disconnect the fuel rail pressure (FRP) sensor. 

2.

Observe the Actual Fuel Rail Pressure with a scan tool.

3.

Does the Actual Fuel Rail Pressure measure more than the 
specified value?

175 MPa

Go to Step 15 

Go to Step 14

    11

Replace the fuel filter. 

Did you complete the replacement?

Go to Step 12 

    12

1.

Ensure that the J 44638 is still installed on the engine.

2.

Start and run the engine under the conditions for which the 
high vacuum occurred in the previous test.

Does the vacuum measure less than or equal to the specified
value?

5 inches at 

idle

12 inches 

at high 

speed

Go to Step 17

Go to Step 13

    13

Repair the restriction in the fuel supply lines between the fuel
tank and the fuel injection pump.

Did you complete the repair?

Go to Step 17 

    14

Inspect the fuel rail pressure sensor signal circuit 509 (YL) for a
short to ground between C76 pin 42 and pin A of the fuel rail
pressure sensor. Repair as necessary.

Did you find and correct the condition?

Go to Step 17 

Go to Step 16 

Step

Action

Value(s)

Yes

No

_____________________________________________

 On-Board Diagnostics  OBD-385

5745804

    15

Replace the faulty fuel rail pressure sensor. 

Did you complete the replacement?

Go to Step 17 

    16

Replace the faulty ECM.

Did you complete the replacement?

Go to Step 17 

    17

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 18

    18

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

No

OBD-386

On-Board Diagnostics

_____________________________________________

DTC P1094 Fuel Rail Pressure Low During Idle or Decel Fuel Cut-Off (DFCO) (Figure OBD-100)

Figure OBD-100:   Fuel Rail Pressure Circuit

Circuit Description

The engine control module (ECM) uses the fuel rail pressure (FRP) sensor to determine fuel pressure to the fuel injectors. This is
then compared to the calculated target fuel pressure as determined by the ECM. The ECM adjusts the FRP by modulating the duty
cycle of the control driver of the fuel pressure regulator. Injector pulse duration is determined by the measured rail pressure and the
target injection fuel into each cylinder. If a sensor circuit malfunction is detected, or the commanded fuel injection pump flow is
not within the proper range for a given engine load and speed, DTC will be set.

Conditions for Setting the DTC

The difference between the FRP sensor and the commanded fuel injection pump flow is more than 30 MPa

Action Taken When the DTC Sets 

• The control module stores the DTC information into memory when the diagnostic runs and fails. 

• The malfunction indicator lamp (MIL) will not illuminate. 

• The control module records the operating conditions at the time the diagnostic fails. The control module stores this informa-

tion in the Failure Records. 

• The driver information center, if equipped, may display a message. 

_____________________________________________

 On-Board Diagnostics  OBD-387

5745804

Conditions for Clearing the DTC 

• 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 non-emission re-

lated diagnostic. 

• Clear the DTC with a scan tool. 

Diagnostic Aids 

• If you have to prime the fuel system, inspect for the following conditions:

• A restricted fuel supply line 

•  A fuel supply line air leak--Refer to Fuel System Diagnosis . 

• If the condition is still intermittent, refer to Intermittent Conditions . 

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

Is DTC P1093 also set?

Go to DTC 

P1093

Go to Step 3

    3

Inspect the for fuel contamination. 

Did you find and correct the condition?

Go to Step 10

Go to Step 4

    4

Attempt to start the engine.

Does the engine start and continue to run?

Go to Step 5

Go to Engine 

Cranks but Does 

Not Run 

    5

Is the customer concern also a surging idle?

Go to Fuel Pres-

sure Regulator 

Diagnosis

Go to Step 6

    6

1.

Start and idle the engine.

2.

Observe the fuel rail pressure (FRP) regulator fuel flow with 
a scan tool.

Does the FRP regulator fuel flow measure more than the speci-
fied value?

12000 mm

Go to Step 7

Go to Diagnos-

tic Aids

    7

Test the fuel pressure regulator solenoid control circuit 511 (YL)
between C75 pin 51 and pin 2 of the fuel pressure regulator for a
short to ground.

Did you find and correct the condition?

Go to Step 10 

Go to Step 8

    8

Test for an intermittent or poor connection at the ECM. 

Did you find and correct the condition?

Go to Step 10 

Go to Step 9

    9

Replace the faulty ECM. 

Did you complete the replacement?

Go to Step 10