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 in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The engine control module (ECM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the ECM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream, and low HO2S voltage indicates a lean exhaust stream. If the ECM detects that HO2S 2 voltage stays between a specified range, DTC P0140 will set.
Conditions for Running the DTC
| • | DTCs P0037, P0038, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0141, P0171, P0172, P0300, P0336, P0340, P0341, P0455, P0500, P0601, P0602, P0606, P0641, P0722, P0723 are not set. |
| • | The Engine Run Time parameter is more than 60 seconds. |
Conditions For Setting The DTC
The ECM detects that the HO2S 2 voltage parameter is between 420-481 mV for 150 seconds.
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 number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Did the HO2S 2 voltage parameter change more than the specified value? | 200 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 |
Is the HO2S 2 voltage parameter above the specified value? | 100 mV | Go to Step 5 | Go to Step 11 |
5 |
Is the HO2S 2 voltage parameter less than the specified value? | 100 mV | Go to Step 6 | Go to Step 7 |
6 |
Is the HO2S 2 voltage parameter less than the specified value? | 100 mV | Go to Step 9 | Go to Step 8 |
7 | Test the HO2S 2 high signal circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 |
8 | Test the HO2S 2 low signal circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 |
9 | Test for an intermittent and for a poor connection at 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 14 | Go to Step 12 |
10 | Test for an intermittent and for a poor connection at the engine control module (ECM). 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 |
11 | Repair the short between the HO2S 2 high signal circuit and the HO2S 2 heater low control circuit. Did you complete the repair? | -- | Go to Step 14 | -- |
12 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
13 |
Important: The ECM may be damaged if the HO2S low signal circuit was shorted to a voltage source. Replace the ECM. Refer to Engine Control Module Replacement . 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 been diagnosed? | -- | System OK | |
