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Hummer H2. Manual - part 1558

6: This steps inspects for conditions than can cause the TWC efficiency to appear degraded.

DTC P0420 or P0430

Step

Action

Values

Yes

Did you perform the Diagnostic System Check-
Engine Controls?

Go to Step 2

Go to Diagnostic

System Check -

Engine Controls

Review the DTC information on the scan tool.
Are any other DTCs set?

Go to Diagnostic

Trouble Code

(DTC) List

Go to Step 3

1. Start and idle the engine.

2. Allow the engine to reach operating

temperature.

3. Increase the engine speed to 1,500 RPM for 1

minute.

4. Ensure Closed Loop operation is enabled.

5. Return the engine to a stabilized idle.

6. Observe the HO2S 2 voltage parameter on the

scan tool for the applicable bank.

Is the applicable HO2S 2 voltage parameter
transitioning below the first specified value and
above the second specified value?

350
mV
600
mV

Go to Step 5

Go to Step 4

1. Clear the DTCs with a scan tool.

2. Start the engine.

3. 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 DTC P0420 or P0430 set?

Go to Step 5

Go to Diagnostic

Aids

Visually and physically inspect the TWC for the
following conditions:

Physical damage

Severe discoloration caused by excessive
temperatures

IMPORTANT:

Verify that the three-way catalytic converter
(TWC) is a high quality part that meets the OEM
specifications.

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0171/P0174 To DTC P0507 (TAC)) - 4.8L, 5.3L, and

6.0L - Hummer H2

Internal rattles caused by loose catalyst
substrate

Restrictions-Refer to Restricted Exhaust in
Engine Exhaust.

Did you find and correct the condition?

Go to Step 10

Go to Step 6

Visually inspect the exhaust system for the
following conditions:

Leaks - Refer to Exhaust Leakage in Engine
Exhaust.

Physical damage

Loose or missing hardware

The heated oxygen sensor (HO2S) 2 for the
applicable bank for proper torque

Did you find and correct the condition?

Go to Step 10

Go to Step 7

Visually inspect the HO2S 2 at the applicable bank
for the following conditions:

The pigtail and wiring harness contacting the
exhaust or any ground.

Road damage

Did you find a condition?

Go to Step 8

Go to Step 9

Replace the applicable HO2S 2 sensor. Refer to
Heated Oxygen Sensor (HO2S) Replacement
Bank 1 Sensor 2 or Heated Oxygen Sensor
(HO2S) Replacement Bank 2 Sensor 2 .
Did you complete the replacement?

Go to Step 10

Replace the TWC. Refer to Catalytic Converter
Replacement (Right Hand) in Engine Exhaust.Did
you complete the replacement?

NOTE:

In order to avoid damaging the replacement
three-way catalytic converter, correct the engine
misfire or mechanical fault before replacing the
three-way catalytic converter.

Go to Step 10

1. Clear the DTCs with a scan tool.

2. Turn OFF the ignition for 30 seconds.

3. Start the engine.

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0171/P0174 To DTC P0507 (TAC)) - 4.8L, 5.3L, and

6.0L - Hummer H2

DTC P0442

System Description

This diagnostic tests the evaporative emission (EVAP) system for a small leak when the key is turned OFF and
the correct conditions are met.

Heat is transferred into a vehicle fuel tank while the vehicle is operating. When the vehicle is turned OFF, a
change in the fuel tank vapor temperature occurs, which results in corresponding pressure changes in the fuel
tank vapor space. This change is monitored by the control module using the fuel tank pressure sensor input. The
control module then makes a judgement on the integrity of the system. With a 0.51 mm (0.020 in) leak in the
system, the amount of pressure change observed is significantly less than that of a sealed system.

If the control module detects a pressure change less than a calibrated amount, DTC P0442 sets.

Conditions for Running the DTC

DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0125, P0335,
P0336, P0443, P0446, P0449, P0452, P0453, P0455, P0496, P0500, P0502, P1106, P1107, P2610 are not
set.

The diagnostic runs once with a 10 hour minimum between tests after a fail.

DTC P0455 must run and pass.

The start up intake air temperature (IAT) is between 4-30°C (39-86°F).

The start up engine coolant temperature (ECT) is less than 30°C (86°F).

The start up IAT and ECT are within 8°C (15°F).

The barometric pressure (BARO) is more than 74 kPa.

The ambient air temperature is between 2-32°C (36-90°F).

The engine run time minimum is 600 seconds.

The odometer displays more than 10 miles.

The vehicle has traveled more than 3 miles this trip.

The ECT is more than 70°C (158°F).

The fuel level is between 15-85 percent.

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 11

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

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0171/P0174 To DTC P0507 (TAC)) - 4.8L, 5.3L, and

6.0L - Hummer H2

The ignition is OFF.

Conditions for Setting the DTC

The control module detects a pressure change that is less than a calibrated amount.

Action Taken When the DTC Sets

The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

The control module records the operating conditions at the time the diagnostic fails. The control module
stores this information in the Freeze Frame/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.

Diagnostic Aids

To help locate intermittent leaks, use the J 41413-200 Evaporative Emissions System Tester (EEST) to
introduce smoke into the EVAP system. Move all EVAP components while observing smoke with the J
41413-SPT High Intensity White Light.

A condition may exist where a leak in the EVAP system only exists under a vacuum condition. By using
the scan tool PURGE/SEAL function to create a vacuum, seal the system and observe the FTP parameter
for vacuum decay, this type of leak may be detected.

To improve the visibility of the smoke exiting the EVAP system, observe the suspected leak area from
different angles with the J 41413-SPT .

For intermittent conditions, refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

3: Introducing smoke in 15 second intervals may allow smaller leak areas to be more noticeable. When
the system is less pressurized, the smoke will sometimes escape in a more condensed manner.

5: This step verifies that repairs are complete and that no other condition is present.

DTC P0442

Step

Action

Yes

Schematic Reference:Emission Hose Routing Diagram

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0171/P0174 To DTC P0507 (TAC)) - 4.8L, 5.3L, and

6.0L - Hummer H2

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