GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Corvette 🢒 DTC 🢒 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 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 below a specified value, DTC P0131 or P0151 sets.

Conditions for Running the DTC
    • DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0200, P0300, P0410, P0440, P0442, P0446, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1415, P1416, P1441, P1514, P1515, P1516, P1517, or P1518 are not set.
    • The Ignition 1 signal parameter is between 9-18 volts.
    • The fuel level parameter is more than 10 percent.
    • The Loop Status Parameter is Closed.

Lean Test Enable

    • The air fuel ratio is between 14.5:1 and 14.7:1
    • The TP indicated angle parameter is between 3-70 percent more than the value observed at idle.

Power Enrichment Test Enable

    • The Power Enrichment Parameter is active.
    • The above condition is met for 1 second.

Conditions for Setting the DTC

Lean Test

The affected HO2S voltage parameter is less than 200 mV for 165 seconds.

or

Power Enrichment Test

The affected HO2S voltage parameter is less than 360 mV for 10 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.

Test Description

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

  1. If the HO2S voltage is fixed well below 200 mV, this indicates a short to ground.

    2.

  2. A disconnected sensor should indicate a bias voltage. If the voltage is low, inspect the HO2S high signal circuit for a short to ground.

Step

Action

Value(s)

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-Engine Controls?

--

Go to  Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Start and run the engine until normal operating temperature is reached.
  2. With a scan tool, observe the HO2S voltage for the sensor that applies to this DTC.

Is the HO2S voltage less than the specified value?

200 mV

Go to Step 4

Go to Step 3

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 Record.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Intermittent Conditions

4

  1. Turn OFF the ignition.
  2. Disconnect the HO2S connector for the sensor that applies to this DTC.
  3. Jumper the HO2S low signal circuit terminal on the engine harness side to a known good ground.
  4. Turn ON the ignition, with the engine OFF.
  5. Observe the HO2S voltage with a scan tool.

Is the HO2S voltage within the specified range?

350-550 mV

Go to Step 5

Go to Step 6

5

  1. The HO2S may be detecting a lean exhaust condition. Check for the following conditions:
    2. • Water intrusion into the HO2S connector
    • Exhaust leak between the HO2S and the engine
    • Vacuum leaks
    • Incorrect fuel pressure
    • Lean fuel injectors
    • Inaccurate MAF sensor
  2. Repair any of the above or similar engine conditions as necessary.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 8

6
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector that contains the HO2S high signal circuit. Refer to Powertrain Control Module Replacement .
  3. Test the HO2S high signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 7

7

Test the HO2S high signal circuit for a short to the HO2S Low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

8

Inspect for poor connections at the harness connector of 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 12

Go to Step 10

9

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 12

Go to Step 11

10

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 12

--

11

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 12

--

12
  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 Record.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 13

13

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