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 in Closed Loop. 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 at or near the bias voltage amount, DTC P0140 will set.
Each HO2S 2 has the following circuits:
| • | HO2S 2 high signal |
| • | HO2S 2 low signal |
| • | HO2S 2 heater ignition voltage |
| • | HO2S 2 heater ground |
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449, P1441 are not set. |
| • | The Engine Run Time parameter is longer than 2 minutes. |
| • | The system voltage is between 9-18 volts. |
| • | The diagnostic runs once per trip. |
| • | There is a throttle position (TP) sensor angle change of more than 8 percent at least 5 times during the test period. |
Conditions for Setting the DTC
The PCM detects that the HO2S 2 signal voltage remains between 408-512 mV for more than 5 minutes.
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.
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A normally functioning HO2S 2 voltage signal will fluctuate above and below the bias voltage amount. The action in the test step should result in a visible reaction from the HO2S 2 output.
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A voltage reading other than the specified amount in this step indicates an open circuit condition in one of the signal circuits or the PCM.
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This step inspects for an open circuit condition in the signal circuits, independent of the PCM.
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The conditions listed in the table may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.
Step | Action | Values | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Component Views or Powertrain Control Module Connector End Views | ||||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||
Does the HO2S 2 voltage fluctuate above and below the specified range? | 375-475 mV | Go to Step 3 | Go to Step 4 | |||||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||||
Is the HO2S 2 voltage less than the specified value? | 25 mV | Go to Step 7 | Go to Step 5 | |||||||||||||
Is the resistance within the specified range? | 0-5 ohms | Go to Step 9 | Go to Step 6 | |||||||||||||
6 | Repair the signal circuit that has an open or high resistance. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 12 | -- | ||||||||||||
Inspect for the following 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 12 | Go to Step 8 | |||||||||||||
8 | 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 and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 | ||||||||||||
9 | Test for an intermittent and for a poor connection at the harness connector of the 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 12 | Go to Step 11 | ||||||||||||
10 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||||
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||||
12 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 13 | ||||||||||||
13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||||
