Circuit Description
Heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias, voltage of approximately 450 mV. While the engine runs, the HO2S 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 HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.
The heating elements within each HO2S heat the sensor. The powertrain control module (PCM) controls the HO2S heater control circuit. The HO2S heater diagnostic monitors the current draw through the HO2S output driver module (ODM) when the engine is running. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.
If the PCM detects that the HO2S 2 voltage remains at or near the bias voltage, DTC P0140 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 |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0140 HO2S Circuit Insufficient Activity Bank 1 Sensor 2
Conditions for Running the DTC
| • | DTCs P0030, P0036, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0135, P0141, P0201, P0202, P0203, P0204, P0205, P0206, P0442, P0443, P0446, P0449, P0455, P0496 are not set. |
| • | DTCs P2A01, P0401, and P0420 are not commanding fuel. |
| • | The system voltage is between 9-18 volts. |
| • | The scan tool special functions are not active. |
Important: This vehicle has 2 methods to enable and run this diagnostic, called regular test and fast pass test.
Fast Pass Test
| • | The Engine Run Time parameter is less than one minute and 30 seconds. |
| OR |
| • | A cold start condition has been detected, identified by the following conditions: |
| - | The Start-up ECT parameter is less than 35°C (95°F). |
| - | The Start-up IAT parameter is less than 35°C (95°F). |
| - | The difference between the Start-up ECT parameter and the Start-up IAT parameter is less than 6°C (10.8°F). |
Important: If the fast pass test does not report a pass, then the regular test is initiated.
Regular Test
| • | The Engine Run Time parameter is more than 2 minutes. |
| • | The TP Sensor parameter has changed more than 3 percent at least 2 times. |
| • | The Loop Status parameter is closed. |
| • | The predicted HO2S temperature is more than 630°C (1,160°F). |
Conditions for Setting the DTC
Fast Pass Test
During the fast pass the HO2S 2 voltage is between 381 mV and 525 mV and less than 180 samples within the first one minute and 30 seconds of engine run time. The PCM detects that the HO2S 2 signal voltage remains between 381 mV and 525 mV within the first 1 minute and 30 seconds of engine run time. If the fast pass test does not report a pass then the regular test is initiated.
Regular Test
| • | During the regular test the HO2S 2 voltage is between 390 mV and 520 mV for at least 1,080 out of 1,200 samples. The PCM detects that the HO2S 2 signal voltage remains between 390 mV and 520 mV for more than 2 minutes. |
| • | Each sample is 100 milliseconds during both tests. |
| • | This diagnostic runs once per trip. |
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 - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||||||
2 |
Does the voltage fluctuate above and below the specified range? | 390-520 mV | Go to Step 3 | Go to Step 4 | ||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||
4 |
Important: The scan tool will not display the HO2S 2 heater command status, but the HO2S 2 driver will still be commanded ON and OFF at the same time as the HO2S 1 driver. Does the test lamp flash ON and OFF? | -- | Go to Step 5 | Go to Step 4 of DTC P0140 | ||||||||||
5 |
Is the voltage less than the specified value? | 15 mV | Go to Step 6 | Go to Step 7 | ||||||||||
6 |
Is the resistance within the specified range? | 0-5 ohms | Go to Step 9 | Go to Step 8 | ||||||||||
7 | Test the HO2S 2 high signal circuit for an open or high resistance. 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 14 | Go to Step 11 | ||||||||||
8 | Test the HO2S 2 low signal circuit for an open or high resistance. 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 14 | Go to Step 11 | ||||||||||
9 | 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 14 | Go to Step 10 | ||||||||||
10 | 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 14 | Go to Step 12 | ||||||||||
11 | 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 14 | Go to Step 13 | ||||||||||
12 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||||||
13 | Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. 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 | Observe the Capture Info with a scan tool. Are there any DTCs that have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK | ||||||||||
