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 of the exhaust stream. When the vehicle is first started, the powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The HO2S 2 is used for post catalyst monitoring. If the PCM detects that the HO2S 2 voltage remains above a calibrated voltage for an excessive amount of time, DTC P0138 will set.
Each HO2S 2 has the following circuits:
| • | An HO2S 2 high signal circuit |
| • | An HO2S 2 low signal circuit |
| • | An HO2S 2 heater ignition voltage circuit |
| • | An HO2S 2 heater low control circuit |
| • | An HO2S low reference circuit |
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0201, P0202, P0203, P0204, P0205, P0206, P0442, P0443, P0446, P0449, P0455, P0496 are not set. |
| • | DTCs P0136, P0401, and P0420 are not commanding fuel. |
| • | The TP Sensor parameter is between 3-40 percent. |
| • | The Air Fuel Ratio parameter is between 12:1 and 16.5:1. |
| • | The Loop Status parameter is closed. |
| • | The system voltage is between 9-18 volts. |
| • | The above conditions have been met for 6 seconds. |
Conditions for Setting the DTC
The PCM detects that the HO2S 2 voltage is more than 910 mV, for more than 2 minutes during Closed Loop operation.
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. |
Step | Action | Values | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views | ||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||
2 |
Is the voltage more than the specified value? | 910 mV | Go to Step 4 | Go to Step 3 | ||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||
4 |
Is the voltage more than the specified value? | 910 mV | Go to Step 5 | Go to Step 6 | ||||||||||
5 |
Important: The HO2S 2 may have been damaged when the HO2S 2 high signal circuit was shorted to voltage. Verify proper operation of the HO2S 2 after completing the repair. Test the HO2S 2 high signal circuit for a short to voltage. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8 | ||||||||||
6 | Inspect for the following conditions that may affect the HO2S operation: Notice: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in the Preface section.
Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.
Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 7 | ||||||||||
7 | Test for an intermittent and for a poor connection at the harness connector of the HO2S 2. Refer to Testing for Intermittent Conditions and Poor Connections , Connector Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9 | ||||||||||
8 | Test for shorted terminals and poor connections at the harness connector of the powertrain control module (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 11 | Go to Step 10 | ||||||||||
9 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||||||
10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||||||
11 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 12 | ||||||||||
12 | Observe the Capture Info with a scan tool. Are there any DTCs that have not diagnosed? | -- | System OK | |||||||||||
