For 1990-2009 cars
Engine Controls Components
Oxygen Sensors
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice

### Circuit Description

The Powertrain Control Module (PCM) supplies a voltage of approximately 0.45 volt between the oxygen sensor (O2S 1) signal and the ground circuit. The oxygen sensor (O2S 1) varies the voltage within a range of approximately 1 volt if the exhaust is rich, to approximately 0.10 volt if the exhaust is lean.

The sensor is like an open circuit and produces no voltage when below 315°C (600°F). An open sensor circuit or a cold sensor causes an Open Loop operation.

Replace the entire oxygen sensor (O2S 1) assembly. Do not attempt to repair the oxygen sensor if the following conditions exist:

• | Damaged wiring

• | Damaged electrical connectors

• | Damaged terminals

### Conditions For Setting The DTC

• | DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0171, P0200, P0300, P0301, P0302, P0303, P0304, P0341, P0404, P0506, P0507, P0601, P0602 not set.

• | Air flow is greater than 3 grams per second.

• | Engine Coolant Temperature (ECT) is greater than 70°C (158°F).

• | Engine is operating in Closed Loop.

• | Throttle Position (TP) angle is between 8% and 50%.

• | Engine has been in the above conditions for 20 seconds.

• | O2S 1 voltage is less than 52 mV for 125 seconds.

### Action Taken When the DTC Sets

• | The Malfunction Indicator Lamp (MIL) will illuminate.

• | The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.

• | A history DTC stores.

• | The coolant fan turns ON.

• | The vehicle will operate in an Open Loop operation.

### Conditions for Clearing the MIL/DTC

• | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.

• | A history DTC will clear after 40 consecutive warm-up cycles without a fault.

• | The MIL/DTCs can be cleared by using the scan tool.

### Diagnostic Aids

• | Fuel pressure--The system will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the vehicle at various road speeds and/or loads to confirm. Refer to Fuel System Diagnosis .

• | MAP sensor--An output that causes the PCM to sense a lower than normal manifold pressure (high vacuum) can cause the system to go lean. Disconnecting the MAP sensor will allow the PCM to substitute a fixed (default) value for the MAP sensor. If the lean condition is gone when the MAP sensor is disconnected, substitute a known good MAP sensor and recheck. Refer to the Manifold Absolute Pressure Sensor Output Diagnosis .

• | Fuel contamination--Water, in even small amounts, near the in-tank fuel pump inlet, can be delivered to the injector. The water causes a lean exhaust and can set DTC P0131.

• | Sensor harness--The O2S 1 sensor pigtail may be mis-positioned and contacting the exhaust manifold.

• | Engine misfire--A misfiring cylinder will result in unburned oxygen in the exhaust, which could cause a DTC P0131. Refer to DTC P0300 Engine Misfire Detected and/or Symptoms .

• | Cracked Oxygen sensor (O2S 1)--A cracked O2S 1 or poor ground at the sensor could cause a DTC P0131. Refer to Symptoms .

• | Plugged fuel filter--A plugged fuel filter can cause a lean condition and cause a DTC P0131 to set.

• | Plugged Oxygen Sensor (O2S 1)--A plugged reference port on the Oxygen Sensor (O2S 1) will indicate a lower then normal voltage output from the O2S 1.

### Test Description

The numbers below refers to the step numbers on the Diagnostic Table.

1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

2. This step determines if the DTC P0131 is the result of a hard malfunction or an intermittent condition. It may be necessary to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.

3. This step simulates a DTC P0134. If the PCM senses the change, the PCM and wiring are OK.

4. Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Techline information for PCM programming and the Crankshaft Position System Variation Learn .

5. If no malfunctions have been found at this point and if no additional DTCs were set, refer to the Diagnostic Aids for additional checks and information.

#### DTC P0131-Oxygen Sensor (O2S) Circuit Low Voltage (Sensor 1)

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Install a scan tool.
2. Start the engine.
3. Idle the engine at the normal operating temperature.

Does the O2S 1 voltage remain below the specified value?

52 mV

Go to Step 4

Go to Step 3

3 |

1. Review the Freeze Frame data and record the parameters.
2. Operate the vehicle within the Freeze Frame conditions and Conditions For Setting the DTC as specified.

Does the O2S 1 voltage stay below specified value?

52 mV

Go to Step 4

Go to Step 7

4 |

1. Turn OFF the ignition switch.

Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury.

2. Disconnect the O2S 1 electrical connector.
3. Turn ON the ignition switch leaving the engine OFF.

Does the scan tool indicate that the O2S 1 voltage is within the specified values?

399-499 mV

Go to Diagnostic Aids

Go to Step 5

5 |

1. Turn OFF the ignition switch.
2. Check the O2S 1 sensor signal circuit for a short to ground.
3. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 7

Go to Step 6

6 |

1. Check for a poor electrical terminal connection (PCM side).
2. If the electrical connection is OK, replace the PCM. Refer to the Powertrain Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 7

--

7 |

1. Turn OFF the ignition switch.

Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury.

2. If the O2S 1 electrical connector is disconnected, reconnect the O2S 1 electrical connector.
3. Turn ON the ignition switch leaving the engine OFF.
4. Clear the DTCs with the scan tool.
5. Start the engine.
6. Idle the engine at the normal operating temperature.
7. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic ran and passed?

--

Go to Step 8

Go to Step 2

8 | Check to see if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to applicable DTC table | System OK