Hummer H1 (2006+). Manual - part 165

3-2 Fuel, Emissions, and Exhaust

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Speci cations

Fuel System Diagnostics

Fuel system diagnosis should begin with a preliminary inspection followed by a road test to confirm existence of a problem. Preliminary
inspection consists of visual checks designed to rule out faults caused by leaks, fuel line damage, or loose electrical connections.

Diagnostic Aids

Important

: Since it is difficult to diagnose intermittent conditions, it is critical that every step of the diagnostic table be performed

with thoroughness. Since many failures can cause similar symptoms.

It is also important to perform visual checks for a pinched harness (at the intake manifold and turbocharger), and for proper wiring
connections at the engine connectors. 

An intermittent problem can be caused by the following:

• Poor connections

• Rubbed through wire insulation

• Broken wire inside the insulation

Road Test

1.

Note the battery voltage. Low voltage can cause ECM power-up and initialization problems. Battery voltage should be no 
lower than 11.5 volts for satisfactory operation.

2.

Connect the scan tool to the diagnostic link connector. Set the tool to record the fault codes, or have a helper use the tool to
interrogate the system during the test.

3.

Start the engine and check the idle operation. Note any faults such as rough idle, stalling or excessive smoke.

4.

Apply the service brake and shift the transmission into a drive range. Note if the engine stalls, runs rough or another fault occurs.

5.

Drive the vehicle on the road at the posted speed limits. Note the operation under light and heavy acceleration, and at normal
cruise speeds. Note the faults such as surge, miss, vibration, noise, low power, smoke (blue, black, white).

6.

Shift into neutral at cruise speed and note the engine operation. If a vibration or noise was experienced but it now stops, the
problem may be with the drive belt, the engine mount, accessory, U-joint or the torque converter.

7.

Return to the shop and note any fault codes recorded by the ECM. If a fuel system fault was noted during the road test, refer to
the diagnosis charts, perform the fuel system tests and check the system electrical components with the scan tool.

Recommended Fuel 

Diesel #2

Injection Pump Type

Bosch Common Rail

Manufacturer

Bosch

Nozzles

Bosch Pintle type 

Opening Pressures

5000 - 23,000 psi

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 Fuel, Emissions, and Exhaust  3-3

Figure 3-1:   Fuel System Components

 Fuel System Diagnosis

Steps

Action

Value(s)

Yes No

1

Did you preform the Powertrain On-Board    
Diagnostic (OBD) System Check?

–––

Go to step 2.

Go to the Diag-

nostic systems 

check.

2

Check the condition of the batteries. 
Is the condition of the batteries OK?

–––

Go to step 3.

Go to step 9.

3

Check for adequate fuel in the fuel tank.
Is the fuel at an adequate level?

–––

Go to step 4.

Go to step 9.

4

Check the quality of the fuel. Refer to chapter 3 
Fuel, Emissions and Exhaust.
Is the fuel quality OK?

–––

Go to step 5.

Go to step 9.

5

Check for the proper cranking speed. 
Is the engine cranking speed OK?

–––

Go to step 6.

Go to step 9.

6

Check for a restriction in the fuel return system. 
Does the fuel return system operate properly?

–––

Go to step 7.

Go to step 9.

7

Check for air in the fuel system. 
Is there any air in the fuel system?

–––

Go to step 10.

Go to step 9.

8

Check for an improper connection or corrosion at 
the engine ground (G1).
Was a problem found and repaired?

–––

Go to step 16.

Go to step 13.

9

Make the appropriate repairs.
Is the action complete?

–––

Go to step 10.

–––

10

Verify the condition has been repaired.
Is the action complete?

–––

Injection Sys-

tem OK.

Go to Driveabil-

ity Symptoms.

FUEL

INJECTION

CONTROL

MODULE

FUEL

MANAGER

FUEL

INJECTION

PUMP

INJECTORS

TANK

SELECTOR

AUXILIARY

TANK

MAIN

TANK

3-4 Fuel, Emissions, and Exhaust

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 Fuel System Driveability Symptoms

PROBLEM

POTENTIAL CAUSE

CORRECTION

Hard Starting

1.

Driver/owner not following the recom-
mended start procedure.

1.

Remind the driver/owner of the required proce-
dure. Demonstrate the procedure if necessary.

2.

Fuel contaminated, low quality or the wrong 
the fuel.

2.

Drain off sample at the fuel filter drain plug. Flush 
the tank, lines, and the filter if the fuel is contami-
nated, wrong grade or type, suspect quality or 
shows wax buildup.

3.

The air filter is plugged.

3.

Remove and clean the filter, housing, air horn and 
the inlet hose. Replace the filter if plugged.

4.

Excessive water in the fuel filter.

4.

Drain off the water at the drain plug. Then remove, 
clean, and reinstall the filter.

5.

The fuel return, drain or the vent line is 
restricted, plugged or damaged.

5.

Check the lines for damage. Verify the flow with 
compressed air. Repair or replace the lines as nec-
essary.

6.

The coolant temperature sensor has a fault.

6.

Inspect the engine coolant temperature (ECT) sen-
sor. Use the scan tool to compare the ECT with the 
ambient air temperature on a cold engine. If the 
coolant temperature reading is more than 5 degrees 
more or less than the ambient air temperature on a 
cold engine, inspect for a high resistance in the 
coolant sensor circuit or the sensor itself.

7.

 A glow plug fault.

7.

Test the voltage to and from the relay/controller, 
and at the plugs. Repair the wiring, replace the 
relay/controller, or replace the glow plug(s) as 
needed. Refer to the test procedures in this section 
and in sections 2 and 12.

8.

No cranking signal to the ECM 

8.

Test with a scan tool. Look for a bad ground, con-
nections, or damaged/failed crankshaft position 
sensor.

9.

Exhaust system is restriction.

9.

Look for damaged pipes, converter, especially on 
the vehicles used off road.

10. Low engine cranking speed.

10. Check state of charge of the batteries, load test and 

check the connections. Refer to the test procedures 
in Section 12. Check the engine oil viscosity to 
ensure it is correct for the ambient temperature. 
Refer to the specifications in Section 1. Check the 
starter draw to determine if the starter is dragging. 
Refer to the test procedure in Section 12.

No Start Condi-
tion (engine 
cranks but will 
not run)

1.

Excessive amount of water or wax buildup in 
the system.

1.

Draw off a sample at the drain plug. Drain and 
flush the system if necessary.

2.

Blown fuse.

2.

Replace the fuse. Check for shorts-grounds in the
affected circuit.

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 Fuel, Emissions, and Exhaust  3-5

3.

Engine fault:

• broken camshaft

• damaged injection pump gears

• timing gear failure

3.

Inspect and repair as needed.

4.

Fuel tank selector valve problem.

4.

Replace the valve if it won’t switch from main to
auxiliary and back. 

5.

No inject signal from the ECM.

5.

Run the scan tool test and replace the failed sensor,
harness wire or the connector.

6.

ECM ground or feed circuit fault (on ground 
or ignition voltage reference signal).

6.

Confirm with the scan tool. Use the multi meter to
locate the fault.

7.

ECM fault.

7.

Confirm with the scan tool before replacement.

Engine Starts 
then Stalls

1.

Air leak in the fuel feed line.

1.

Inspect the lines and repair as needed. 

2.

Glow plug fault (cold ambient temperature).

2.

Test and repair the wiring, or replace the failed
glow plugs or the relay/controller.

3.

Restriction in fuel tank vent or return lines.

3.

Inspect  and  clear  the  restriction.  Replace  the  cap
vent or the lines as needed.

Low Power, 
Sluggish Accel-
eration

1.

Contaminated or low-quality fuel.

1.

Drain, flush and refill the fuel system.

2.

High fuel temperature.

2.

Normal condition in high ambient.

3.

Restriction in the air intake system.

3.

Remove and clean the filter, housing, weathercap,
hose, air horn.

4.

Fuel tank vent or return line restriction.

4.

Clear the restrictions, replace lines.

5.

Exhaust system restriction.

5.

Inspect the entire system for damage and repair as
needed. If the vehicle is used for off-road
operation, look for kinking, bent or flattened pipes.

6.

Air leak at the injector or line.

6.

Tighten loose fittings or replace the lines if
necessary.

7.

Brake drag.

7.

Inspect the brake components. Look for seized or
binding caliper piston, master cylinder problem, or
failed hydro-boost.

8.

Torque converter stator problems. Will cause 
high fuel consumption and require more 
than normal throttle opening for accelera-
tion.

8.

Perform the torque converter diagnosis procedure
in SECTION 5.

9.

Engine compression low.

9.

Run a compression test. Repair valves, cam, rings
as needed.

10. Turbo diesel electronic accelerator fault such 

as short, ground, loose connection indicate 
potentiometer failure.

10. Check the pedal potentiometer wires and

connections. Test with a scan tool if the check
throttle light is on. Repair the wiring, or replace
the pedal assembly.

 Fuel System Driveability Symptoms  (Continued)

PROBLEM

POTENTIAL CAUSE

CORRECTION