For 1990-2009 cars

### Circuit Description

Heated oxygen sensors (HO2S) are used in order to minimize the time required for Closed Loop fuel control operation and to allow accurate catalyst monitoring. The oxygen sensor heater greatly decreases the time required for fuel control sensor HO2S 1 to become active. The oxygen sensor heater is required by catalyst monitor sensor HO2S 2 to maintain a sufficiently high temperature. This allows accurate exhaust oxygen content readings further from the engine.

The powertrain control module (PCM) will run the heater test only after a cold start, determined by engine coolant temperature and the intake air temperature at the time of startup, and will test only once during an ignition cycle. When the engine is started the PCM will monitor the HO2S voltage. When the HO2S voltage indicates a sufficiently active sensor, the PCM determines how much time has elapsed since startup. If the PCM determines that too much time was required for the HO2S 2 to become active, DTC P0141 will set. The time the HO2S needs to reach the operating temperature is based on the engine coolant temperature at startup and the average mass air flow since start-up. A higher average airflow or higher startup engine coolant temperature means less time to HO2S activity.

### Conditions for Running the DTC

• | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201-P0206, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set.

• | The system voltage is 9-18 volts.

• | The intake air temperature (IAT) is less than 35°C (95°F) at start-up.

• | The engine coolant temperature (ECT) is less than 35°C (95°F) at start-up.

• | The IAT and the ECT are within 6°C (42°F) of each other at startup.

### Conditions for Setting the DTC

The HO2S 2 voltage remains within 150 mV of the bias voltage, or approximately 450 mV, for too long. The amount of time ranges between 100-130 seconds depending on the engine coolant temperature at start-up and the average air flow since start-up.

### 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.

### Test Description

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

1. The HO2S should be allowed to cool before performing this test. If the HO2S heater is functioning, the signal voltage will gradually increase or decrease as the sensor element warms. If the heater is not functioning, the HO2S signal will remain near the 450 mV bias voltage.

2. This step ensures that the ignition 1 voltage circuit to the HO2S is not open or shorted. The test lamp should be connected to a good chassis ground, in case the HO2S low signal or HO2S heater ground circuit is malfunctioning.

3. This step tests the HO2S heater ground circuit.

4. This step tests for an open or shorted HO2S heater element.

1. An open HO2S high or low circuit can cause the DTC to set with a good HO2S signal. Check the HO2S signal circuits and check the HO2S low circuits before replacing the sensor.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Important: If the engine has just been operating, allow engine to cool for about one hour before proceeding.

1. Turn ON the ignition, with the engine OFF.
2. Monitor HO2S 2 voltage on the scan tool.

Does the HO2S voltage go from bias voltage to greater than the first specified value or less than the second specified value within 2 minutes?

600 mV

300 mV

Go to Intermittent Conditions

Go to Step 3

3 | Inspect fuse for HO2S 2 ignition 1 voltage circuit. Is the fuse open? | -- | Go to Step 15 | Go to Step 4
4 |

1. Raise the vehicle.
2. Disconnect the HO2S 2 electrical connector.

Important: Use a known good ground. Do not use the HO2S 2 heater ground or the low reference circuit.

3. Probe the ignition 1 voltage circuit at the HO2S 2 electrical connector on the PCM harness side with a test lamp connected to ground.

Does the test lamp illuminate?

--

Go to Step 5

Go to Step 7

5 | Connect test lamp between the HO2S 2 ignition 1 voltage circuit and the HO2S 2 heater ground. Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 8
6 |

1. Allow the HO2S to cool for at least 10 minutes.
2. Use a DMM in order to measure the resistance between the brown wires HO2S 2 ignition 1 voltage circuit and HO2S 2 heater ground at the HO2S 2 pigtail.

Does the resistance measure within the specified values?

4-6 ohms

Go to Step 9

Go to Step 14

7 | Repair the open HO2S 2 ignition 1 voltage circuit to HO2S 2. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | --
8 | Repair the open HO2S 2 heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | --
9 | Inspect the HO2S 2 harness terminals for a poor connection. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 10
10 |

1. Turn OFF the ignition.
2. Disconnect the PCM and test the HO2S 2 high signal circuit and the HO2S 2 low reference circuit for continuity.
3. If the HO2S 2 high signal circuit or HO2S low signal circuit measures over 5 ohms, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 11

11 |

1. Inspect the HO2S 2 high signal or HO2S 2 low signal circuit for a poor connection at the HO2S 2 harness connector.
2. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 12

12 |

1. Inspect the HO2S 2 low signal circuit for a poor connection at the PCM.
2. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 13

13 |

1. Inspect the HO2S 2 high signal circuit for a poor connection at the PCM.
2. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 14

14 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 16 | --
15 | Repair the short to ground in the HO2S 1 or HO2S 2 ignition 1 voltage circuit, and replace the fuse. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | --
16 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 17

Go to Step 2

17 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK