GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2002 🢒 Blazer - 4WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 DTC P0134 or P0154

Circuit Description

The heated oxygen sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with signal high and low circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm the sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When the HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors the HO2S signal voltage for Closed Loop fuel control. During normal Closed Loop fuel control operation, the control module will add fuel, or enrich the mixture, when the HO2S detects a lean exhaust content. The control module will subtract fuel, or lean out the mixture, when the HO2S detects a rich exhaust condition.

This diagnostic trouble code (DTC) monitors the HO2S voltage and detects if the voltage goes out of the bias range 350-550 mV. If the powertrain control module (PCM) does not detect the voltage went out of the bias range, a DTC sets.

Conditions for Running the DTC
    • DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0440, P0442, P0446, P0452, P0453, or P1441 are not set.
    • The engine run time is more than 409 seconds.
    • The ignition 1 signal is between 9-18 volts.
    • Intrusive tests are not in progress.
    • The scan tool output controls are not active.

Conditions for Setting the DTC

The HO2S signal voltage is steady between 350-550 mV for 60 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.
    • The control module commands Open Loop.

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

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

    • An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and connections for breaks or contamination. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems.
    • An HO2S that is loose causes this DTC to set.
    •  For an intermittent condition, refer to Symptoms - Engine Controls .

Test Description

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

  1. After the HO2S heater is commanded ON, the HO2S heater heats up causing the HO2S signal voltage to either increase or decrease. This indicates that the HO2S heater is OK.

    2.

  2. If the HO2S voltage is varying outside the specified range, the condition is not present.

    3.

  3. If the test lamp illuminates, the low reference circuit between the HO2S and PCM terminal C1-63 is OK and the PCM low reference terminal is OK.

    4.

  4. If the voltage is below the specified value, the high signal circuit, the low reference circuit, and the PCM are OK.

    5.

  5. The opposite bank HO2S must be disconnected to isolate a short to ground in the HO2S heater high control circuit.

    6.

  6. Resistance within the specified range indicates the HO2S heater is OK.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Important: Allow the engine to cool for one-half hour before proceeding with this diagnostic. This allows the HO2S signal voltage to return to bias voltage, approximately 447 mV.

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Command the HO2S heater ON with a scan tool.
  4. Immediately observe the affected HO2S voltage for 2 minutes.

Does the HO2S voltage go from bias voltage to more than or less than the specified range?

300-600 mV

Go to Step 3

Go to Step 5

3

  1. Start the engine.
  2. Allow the engine to reach operating temperature.
  3. Raise and hold the engine speed at 1,200 RPM for 2 minutes.
  4. Observe the HO2S voltage with a scan tool.

Is the HO2S voltage varying outside the specified range?

350-550 mV

Go to Step 4

Go to Step 5

4
  1. Observe the Freeze Frame/Failure Records data 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 as specified in the supporting text, or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

--

Go to Step 5

Go to Intermittent Conditions

5

Are both DTCs P0134 and P0154 set?

--

Go to Step 6

Go to Step 7

6

  1. Turn OFF the ignition.
  2. Disconnect the bank 1 sensor 1 HO2S connector.
  3. Probe the HO2S low reference circuit with a test lamp that is connected to battery positive.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 10

7

  1. Turn OFF the ignition.
  2. Disconnect the affected HO2S connector.
  3. Jumper the HO2S high signal circuit to the low reference circuit.
  4. Turn the ignition ON, with the engine OFF.
  5. Observe the HO2S voltage with a scan tool.

Is the HO2S voltage less than the specified value?

200 mV

Go to Step 11

Go to Step 8

8
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector containing the HO2S high signal circuit. Refer to Powertrain Control Module Replacement .
  3. Test the HO2S high signal circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 9

9

Test for an open between terminal A of the affected sensor harness connector and one of the following PCM terminals:

    • If DTC P0134 is set use C1-29
    • If DTC P0154 is set use C1-26

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

10
  1. Disconnect the PCM connector containing the HO2S low reference circuit. Refer to Powertrain Control Module Replacement .
  2. Test the low reference circuit for an open between HO2S bank 1 sensor 1 terminal A and PCM terminal C1-63. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

11

  1. If applicable, remove the jumper from the previous step.
  2. Disconnect the opposite bank HO2S connector.
  3. Perform the following:
    4. • If only one DTC is set, P0134 or P0154, probe the affected HO2S heater high control circuit with a test lamp that is connected to a good ground.
    • If both DTC P0134 and P0154 are set, probe HO2S bank 1 sensor 1 heater high control circuit with a test lamp that is connected to a good ground.
  4. Command the HO2S heater ON with a scan tool.

Does the test lamp illuminate?

--

Go to Step 12

Go to Step 13

12
  1. Connect a test lamp between the affected HO2S heater high control circuit and the HO2S heater low reference circuit.
  2. Command the HO2S heater ON with a scan tool.

Does the test lamp illuminate?

--

Go to Step 14

Go to Step 16

13
  1. Disconnect the PCM connector containing the HO2S heater high control circuit. Refer to Powertrain Control Module Replacement .
  2. Test the HO2S heater high control circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

14

Important: Perform the following test on HO2S bank 1 sensor 1 and HO2S bank 2 sensor 1. A condition in either sensor will cause this DTC to set.

Test the HO2S heater high control circuit, sensor side, for a short to the HO2S body. Refer to Circuit Testing in Wiring Systems.

Did you find the condition?

--

Go to Step 20

Go to Step 15

15

Important: Perform the following test on HO2S bank 1 sensor 1 and HO2S bank 2 sensor 1. A condition in either sensor will cause this DTC to set.

Measure the resistance between the HO2S heater high control circuit, sensor side, and the HO2S heater low reference circuit, sensor side. Refer to Circuit Testing in Wiring Systems.

Does the resistance of either sensor measure above or below the specified range?

2-50  ohms

Go to Step 20

Go to Step 18

16
  1. Disconnect the PCM connector containing the HO2S heater low reference circuit. Refer to Powertrain Control Module Replacement .
  2. Test the HO2S heater low reference circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

17

Inspect for poor connections at the harness connector of the 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 21

Go to Step 19

18

Inspect for poor connections at the harness connector of the affected 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 21

Go to Step 20

19

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 21

--

20

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

Did you complete the replacement?

--

Go to Step 21

--

21
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 22

Go to Step 2

22

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK