GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Malibu 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 DTC P0131 or P0151

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 of the exhaust stream. When the vehicle is first started, the powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature and provide an accurate voltage signal. If the PCM detects that the HO2S 1 voltage remains below a calibrated amount for an excessive amount of time, DTC P0131 will set for bank 1 sensor 1, or DTC P0151 will set for bank 2 sensor 1.

Each HO2S 1 has the following circuits:

    • The HO2S 1 high signal circuit
    • The HO2S 1 low signal circuit
    • The HO2S 1 ignition 1 voltage circuit
    • The HO2S 1 heater low control circuit

Conditions for Running the DTC
    • DTCs  P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0125, P0128, P0201-P0206, P0442, P0443, P0446, P0449 are not set.
    • The system voltage is between 9-18 volts.
    • The Engine Run Time parameter is at least 5 minutes.
    • The TP Indicated Angle parameter is between 4-40 percent.
    • The Loop Status parameter is closed.
    • The traction control is not active.
    • The ECT Sensor parameter is less than 128°C (262°F).
    • The Air Fuel Ratio parameter is between 12.94:1-15.99:1.
    • The above conditions have been met for 3 seconds.

Conditions for Setting the DTC

The PCM detects that the HO2S 1 voltage is less than 78 mV for more than 51 seconds.

OR

The PCM detects that the HO2S 1 voltage is less than 600 mV during power enrichment (PE) mode for more than 7.5 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.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check-Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Start the engine.
  2. Allow the engine to idle at operating temperature. Refer to Scan Tool Data List .
  3. Clear the DTC and record the Freeze/Frame Failure Records.
  4. Observe the affected HO2S parameter with a scan tool.

Is the voltage varying above and below the specified range?

300-600 mV

Go to Step 3

Go to Step 4

3
  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

4
  1. Turn OFF the ignition.
  2. Disconnect the affected heated oxygen sensor (HO2S) 1.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the affected HO2S parameter with a scan tool.

Is the voltage within the specified range?

75-115 mV

Go to Step 5

Go to Step 6

5

Test the HO2S 1 high signal circuit for a short to the HO2S 1 heater low control circuit. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

6

Is the voltage less than the specified value?

75 mV

Go to Step 7

Go to Step 8

7

Test the HO2S 1 high signal circuit for a short to ground or a short to the HO2S 1 low signal circuit. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

8

Inspect for the following conditions that may affect the HO2S operation:

Notice: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in the Preface section.

    • HO2S contamination

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

    • Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring
    • Exhaust system leaks or restrictions
    • Any water intrusion into the HO2S connector
    • Any vacuum leaks
    • Any lean fuel injectors--Refer to Fuel Injector Balance Test with Tech 2 .
    • An inaccurate mass air flow (MAF) sensor
    • Evaporative emissions (EVAP) system malfunction--Inspect the EVAP control system. Refer to Inspection/Maintenance Evaporative Emission System Set .
    • Incorrect fuel pressure--Refer to Fuel System Diagnosis .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 9

9

Test for shorted terminals and poor connections at the HO2S 1. Refer to Testing for Intermittent Conditions and Poor Connections , Connector Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 11

10

Test for shorted terminals and 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 13

Go to Step 12

11

Notice: Refer to Heated Oxygen Sensor Resistance Learn Reset Notice in the Preface section.

Replace the HO2S 1. 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 13

--

12

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 13

--

13
  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 14

14

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK