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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Optra 🢒 Engine 🢒 Engine Controls - 1.6L (L91) 🢒 DTC P0131

Circuit Description

The oxygen sensors (O2S) is used for fuel control and catalyst monitoring. The O2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the control module operates in an Open Loop mode, ignoring the O2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the O2S with a reference, or bias voltage of about 450 mV. While the engine runs, the O2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient O2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the O2S voltage to determine the air-to-fuel ratio. An O2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An O2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.

The O2S utilizes the following circuits:

    • A signal circuit
    • A low reference circuit

If the ECM detects the O2S voltage is low or is near bias voltage, a DTC sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0131 O2S Circuit Low Voltage Sensor 1

Conditions for Running the DTC
    • DTCs P0107, P0108, P0117, P0118, P0122, P0123, P0335, P0336, P0337, P0341, P0342, P0400, P0404, P0405, P0406, P0444, P0445, P1320, P1321, P1402, and P1403 are not set.
    • The ignition 1 voltage is between 11-16 volts.
    • The fuel system is in Closed Loop.
    • The engine speed is less than 6000 RPM.
    • The DTC runs continuously when the above conditions are met.

Conditions for Setting the DTC
    • The O2 sensor voltage is less than 0.07 volt for at least 40 seconds.
        OR
    • The O2 sensor voltage is between 0.352-0.499 volts for 10 seconds.

Action Taken When the DTC Sets
    • The malfunction indicator lamp (MIL) will illuminate.
    • The coolant fan turns ON.

Conditions for Clearing the MIL/DTC
    • The MIL will turn off after 4 consecutive ignition cycles in which the diagnostic runs without a fault.
    • DTCs can be cleared by using the scan tool.
    • Disconnect the ECM battery feed for more than 10 seconds.

Test Description

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

  1. This step tests for a short to ground to the signal circuit of the O2S.

    2.

  2. This step tests the O2S signal and the low reference circuit for an open. The O2S voltage should go low.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine 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 the engine.
  2. Allow the engine to reach the normal operating temperature.
  3. Operate the engine above 1,200 RPM for 30 seconds and then allow the engine to idle.
  4. Observe the Loop Status parameter with a scan tool.

Does the scan tool display Closed Loop?

--

Go to Step 3

Go to Step 4

3
  1. Turn OFF the ignition for 30 seconds.
  2. Start the engine.
  3. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC fail this ignition?

--

Go to Step 4

Go to Intermittent Conditions

4

  1. Turn OFF the ignition.
  2. Disconnect the harness connector of the oxygen sensor (O2S).
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the O2S voltage parameter with a scan tool.

Is the voltage within the specified range?

350-550 mV

Go to Step 5

Go to Step 8

5

  1. Connect a 5-amp fused jumper wire between the signal circuit and the low reference circuit of the O2S.
  2. Observe the O2S voltage parameter with a scan tool.

Is the voltage less than the specified value?

20 mV

Go to Step 7

Go to Step 6

6
  1. Connect a 5-amp fused jumper wire between the O2S signal circuit and a good ground.
  2. Observe the O2S voltage parameter with a scan tool.

Is the voltage less than the specified value?

20 mV

Go to Step 9

Go to Step 8

7

Test or inspect for the following conditions:

    • Lean fuel injectors--Refer to Fuel Injector Balance Test with Special Tool .
    • Low fuel system pressure--Refer to Fuel System Diagnosis .
    • Fuel that is contaminated
    • Exhaust leaks near the O2S--Refer to Symptoms - Engine Exhaust in Engine Exhaust.
    • Engine vacuum leaks

Did you find and correct the condition?

--

Go to Step 14

Go to Step 10

8

Test the O2S signal circuit for one of the following conditions:

    • A short to ground
    • An open
    • High resistance

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 11

9

Test the O2S low reference circuit for one of the following conditions:

    • A short to voltage
    • An open
    • High resistance

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 11

10

Test for shorted terminals and poor connections at the O2S. 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 14

Go to Step 12

11

Test for shorted terminals and poor connections at the engine control module (ECM). 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 14

Go to Step 13

12

Replace the O2S. Refer to Oxygen Sensor Replacement .

Did you complete the replacement?

--

Go to Step 14

--

13

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 14

--

14
  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.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 15

15

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK