Circuit Description
The powertrain control module (PCM) supplies a bias voltage of about 450 mV between the heated oxygen sensor (HO2S) high signal circuit and the HO2S low signal circuit. When measured with a 10 mega ohm digital voltmeter, this may display as low as 350 mV. The oxygen sensor signal varies from about 800 mV when the exhaust is rich, to about 50 mV when the exhaust is lean.
If the HO2S 2 voltage remains at or near the 450 mV bias for an extended period of time, DTC P0140 will set.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set. |
| • | The engine has been running for at least 4 minutes. |
Conditions for Setting the DTC
| • | HO2S 2 signal voltage remains between 412-500 mV for up to 90 seconds. |
| • | Ignition voltage should be more than 9 volts and less than 18 volts |
| • | Test only runs once per trip. |
| • | A throttle position (TP) sensor change of more than 8 percent at least twice during the test. |
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.
-
This step checks for the correct sensor activity. When in Closed Loop fuel control, the HO2S voltage should rapidly swing above and below the bias voltage.
-
This step checks for correct HO2S heater circuit operation up to the HO2S connector.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Does the voltage vary outside the specified values? | 412-500 mV | Go to Step 3 | Go to Step 4 | |
3 |
Does the DTC reset? | -- | Go to Step 4 | Go to Intermittent Conditions |
4 |
Does the voltage measure less than the specified value? | 150 mV | Go to Step 8 | Go to Step 5 |
5 |
Does the voltage measure near the specified value? | 400 mV | Go to Step 6 | Go to Step 7 |
6 |
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 9 |
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | |
8 |
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11 |
9 |
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 |
10 |
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 |
11 | Replace HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
12 | Replace the PCM. Refer to Powertrain Control Module Replacement Did you complete the replacement? | -- | Go to Step 13 | -- |
13 |
Does the DTC run and pass? | -- | Go to Step 14 | Go to Step 2 |
14 | With a scan tool, observe the stored information in Capture Info, Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK |
