Hummer H2. Manual - part 1540

resistance. Refer to Circuit Testing and Wiring
Repairs in Wiring Systems.
Did you find and correct the condition?

Go to Step 20

Go to Step 17

Test the HO2S high signal circuit for an open or high
resistance. Refer to Circuit Testing and Wiring
Repairs in Wiring Systems.
Did you find and correct the condition?

Go to Step 20

Go to Step 17

1. The HO2S may be detecting a lean exhaust

condition or may be contaminated. Inspect for the
following conditions:

A silicon contaminated HO2S

Any water intrusion into the HO2S
connector

An exhaust leak between the HO2S and the
engine

Any vacuum leaks

An incorrect fuel pressure-Refer to Fuel
System Diagnosis .

Any lean fuel injectors-Refer to Fuel
Injector Balance Test with Tech 2 .

An inaccurate mass air flow (MAF) sensor-
Refer to Scan Tool Data List .

2. Repair any of the above or similar engine

conditions as necessary.

Did you find and correct the condition?

NOTE:

Refer to Silicon Contamination of Heated
Oxygen Sensors Notice in Cautions and
Notices.

Go to Step 20

Go to Step 16

Test for shorted terminals and for poor connections at
the HO2S. Refer to Testing for Intermittent
Conditions and Poor Connections and Connector
Repairs in Wiring Systems.
Did you find and correct the condition?

Go to Step 20

Go to Step 18

Test for shorted terminals and for poor connections at
the powertrain control module (PCM). Refer to Testing
for Intermittent Conditions and Poor Connections
and Connector Repairs in Wiring Systems.
Did you find and correct the condition?

Go to Step 20

Go to Step 19

Replace the affected HO2S. Refer to Heated Oxygen
Sensor (HO2S) Replacement Bank 1 Sensor 2 or

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0068 To DTC P0141/P0161) - 4.8L, 5.3L, and 6.0L -

Hummer H2

DTC P0138 OR P0158

Circuit Description

Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the
oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach
operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the
time required for the sensors to reach operating temperature. The powertrain control module (PCM) supplies the
HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in
open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and closed loop is
achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias
voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream.
If the PCM detects an HO2S voltage that stays above a specified value, DTC P0138 sets for HO2S bank 1
sensor 2 or DTC P0158 sets for HO2S bank 2 sensor 2.

Conditions for Running the DTC

Rich Test Enable:

DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120,
P0200, P0220, P0300, P0442, P0446, P0452, P0453, P0455, P0496, P1125, P1258, P1516, P2101,
P2108, P2135, U0107 are not set.

The Loop Status parameter is closed.

The Ignition 1 Signal parameter is between 10-18 volts.

The Fuel Tank Level Remaining parameter is more than 10 percent.

Heated Oxygen Sensor (HO2S) Replacement Bank 2
Sensor 2 .
Did you complete the replacement?

Go to Step 20

Replace the PCM. Refer to Powertrain Control
Module (PCM) Replacement .
Did you complete the replacement?

Go to Step 20

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 21

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 P0068 To DTC P0141/P0161) - 4.8L, 5.3L, and 6.0L -

Hummer H2

The TP Indicated Angle parameter is between 3-70 percent more than the value observed at idle.

Decel. Fuel Cutoff Test Enable:

The Loop Status parameter is closed.

The Ignition 1 Signal parameter is between 10-18 volts.

The Fuel Tank Level Remaining parameter is more than 10 percent.

The Engine Run Time parameter is more than 30 seconds.

The Decel. Fuel Cutoff parameter is active for more than 4 seconds.

Conditions for Setting the DTC

Rich Test

The PCM detects that the affected HO2S voltage parameter is more than 950 mV for 200 seconds.

Decel. Fuel Cutoff Test

The PCM detects that the affected HO2S voltage parameter is more than 480 mV for 5 seconds.

Action Taken When the DTC Sets

The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition
cycle that the diagnostic 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 consecutive 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.

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0068 To DTC P0141/P0161) - 4.8L, 5.3L, and 6.0L -

Hummer H2

Test Description

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

2: If the voltage does not change more than the specified value, the condition is present.

DTC P0138 or P0158

Step

Action

Value

(s)

Yes

Schematic Reference:Engine Controls Schematics
Connector End View Reference:Engine Controls Connector End Views or Powertrain Control
Module (PCM) Connector End Views

Did you perform the Diagnostic System Check-Engine
Controls?

Go to Step 2

Go to Diagnostic

System Check -

Engine Controls

1. Start the engine.

2. Allow the engine to reach operating temperature.

Refer to Scan Tool Data List .

3. Operate the engine at 1,500 RPM for 30 seconds.

4. While observing the affected HO2S voltage

parameter with a scan tool, quickly cycle the
throttle from closed throttle to wide open throttle,
3 times.

Did the HO2S voltage parameter change more than the
specified value?

IMPORTANT:

With the engine running, observe the HO2S Bank 1
Sensor 1 and HO2S Bank 2 Sensor 1 voltage
parameters with a scan tool. The voltage should vary
from below 300 mV to above 600 mV. If the voltage is
not varying, refer to DTC P0131 or P0151 .

200
mV

Go to Step 3

Go to Step 4

1. Observe the Freeze Frame/Failure Records 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. 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 4

Go to

Intermittent

Conditions

1. Turn OFF the ignition.

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0068 To DTC P0141/P0161) - 4.8L, 5.3L, and 6.0L -

Hummer H2

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