Circuit Description
The oxygen sensor (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, and P0406 are not set. |
| • | The fuel system is in closed loop. |
| • | The engine speed is less than 6000 RPM. |
| • | The DTC runs continuously once the above conditions are met. |
Conditions for Setting the DTC
| • | The O2 sensor voltage is below 0.07 volts for at least 40 seconds |
| OR |
| • | The O2 sensor voltage is between 0.352-0.499 volts for more than 10 seconds. |
Action Taken when the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores the information in the Freeze Frame/Failure Records records. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | Clear the MIL and the DTC with a 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.
-
This step tests for a short to ground to the signal circuit of the O2S.
-
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 | |||||||||||
2 |
Does the scan tool display Closed Loop? | -- | Go to Step 3 | Go to Step 4 | ||||||||||
3 |
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||
Is the voltage within the specified range? | 350-550 mV | Go to Step 5 | Go to Step 8 | |||||||||||
Is the voltage less than the specified value? | 20 mV | Go to Step 7 | Go to Step 6 | |||||||||||
6 |
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:
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:
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:
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 Heated Oxygen Sensor 1 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 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 15 | ||||||||||
15 | Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||
