Circuit Description
The heated oxygen sensor (HO2S) is a sensor used to detect oxygen-content in the exhaust. The powertrain control module (PCM) supplies the sensor with a signal circuit and a ground circuit. The PCM supplies a bias voltage between the circuits. The sensor varies the voltage based on the oxygen content in the exhaust. When the exhaust stream is lean (more oxygen), the sensor produces a low voltage signal. When the exhaust stream is rich (less oxygen), the sensor produces a high voltage signal. The PCM monitors the HO2S signal during Closed Loop. To correct for rich or lean conditions, the PCM adjusts the injector pulse width.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0201-P0208, P0410, P0440, P0442, P0443, P0446, P0449, P1415, P1416, or P1441 are not set. |
| • | The throttle position (TP) angle is between 3-25 percent. |
| • | The system voltage is between 9-18 volts. |
| • | The Closed Loop fuel control is enabled. |
| • | The air/fuel ratio is between 14.4-14.9. |
| • | The exhaust gas recirculation (EGR) flow diagnostic test is not active. |
| • | The secondary air injection (AIR) diagnostic test is not active. |
| • | The catalyst diagnostic test is not active. |
| • | The conditions above are met for 5 seconds. |
Conditions for Setting the DTC
The HO2S bank 1 sensor 2 signal voltage remains above 950 mV for approximately 50 seconds during normal closed loop fuel control.
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. |
Diagnostic Aids
Notice: Do not solder heated oxygen sensor wires. Soldering the wires will result in the loss of the air reference to the sensor. Refer to Engine Electrical for proper wire and connection repair techniques.
Notice: Use the connector test adapter kit J 35616-A for any test that
requires probing the following items:
• The PCM harness connectors • The electrical center fuse/relay cavities • The component terminals • The component harness connector
Check for the following items:
| • | The HO2S routing--The sensor wiring may be routed incorrectly and contacting the exhaust system. |
| • | Silicon contamination--Silicon contamination of the HO2S sensor can also cause a high HO2S signal voltage. This condition is indicated by a powdery white deposit on the portion of the HO2S exposed to the exhaust stream. |
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may assist in diagnosing the condition. The information may help to determine how often the condition that set the DTC occurs.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step verifies whether the HO2S sensor voltage is switching from below 300 mV to above 600 mV, or remains above 600 mV.
-
This step verifies the bias voltage from the PCM and the condition of the circuit wiring. With the sensor disconnected, the scan tool should display a bias voltage near 450 mV.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Does the voltage measure greater than the specified value? | 600 mV | Go to Step 4 | Go to Step 3 | |
3 |
Does the scan tool indicate that DTC P0138 failed this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids |
Does the scan tool display an HO2S bank 1 sensor 2 voltage near the specified value? | 450 mV | Go to Diagnostic Aids | Go to Step 5 | |
5 |
Does the DMM display a voltage near the specified value? | 0 mV | Go to Step 6 | Go to Step 7 |
6 | Test for a short between the HO2S bank 1 sensor 2 high signal circuit and a PCM 5-volt or 12-volt reference circuit. Refer to Engine Controls Schematics . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 8 |
7 | Repair the short to voltage on the HO2S bank 1 sensor 2 high signal circuit. Did you find and correct the condition? | -- | Go to Step 9 | -- |
8 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- |
9 |
Does the DTC run and pass? | -- | Go to Step 10 | Go to Step 2 |
10 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
