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 circuitry that monitors the HO2S generates a reference, or bias, voltage of 450 mV when the sensor is cold, high resistance. Once the HO2S warms up, the HO2S generates a voltage within a range of 0 mV to 1000 mV, depending on the exhaust gas oxygen content. High HO2S voltage output indicates a rich fuel mixture; low HO2S voltage output indicates a lean mixture. Once fueling goes Closed Loop, the HO2S voltage will fluctuate above and below the bias voltage. A heating element inside the HO2S reduces the time required for the sensor to reach operating temperature, and provide an accurate voltage signal.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0200, P0300, P0351-P0358, P0400, P0401, P0404, P0405, P0410, P0440, P0442, P0443, P0446, P0449, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1441, P1514, P1515, P1516, P1517, or P1518 are not set. |
| • | The secondary air injection (AIR) and the exhaust gas recirculation (EGR) diagnostics are not active. |
| • | The intake air temperature (IAT) and the engine coolant temperature (ECT) are less than 50°C (122°F), and are within 8°C (14.5°F) of each other at engine start-up. |
| • | The ignition voltage is between 11-18 volts. |
| • | The HO2S voltage is between 425-475 mv at engine start-up. |
Conditions for Setting the DTC
The HO2S voltage remains between 375-525 mV for a predetermined amount of time depending on ECT and airflow.
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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After the HO2S heater is commanded ON, the HO2S heater heats up, causing the HO2S signal voltage to either increase or decrease. This indicates that the HO2S heater is OK.
-
Resistance within the specified range indicates the HO2S heater is OK.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
|
Important: If DTC P0300 is set, diagnose that DTC first. Refer to Diagnostic Trouble Code (DTC) List . Important: Allow the engine to cool for one-half hour before proceeding with this diagnostic. This allows the HO2S signal voltage to return to bias voltage, approximately 447 mV.
Does the HO2S voltage go from bias voltage to more than or less than the specified range? | 350-550 mV | Go to Step 3 | Go to Step 4 | |
3 |
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions |
4 |
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 6 |
5 |
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 9 |
6 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 7 |
7 |
Important: Perform the following test on HO2S bank 1 sensor 2. Test the HO2S heater voltage circuit, sensor side, for a short to the HO2S body. Refer to Circuit Testing in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 8 |
8 |
Important: Perform the following test on HO2S bank 1 sensor 2. Measure the resistance between the HO2S heater voltage circuit, sensor side, and the HO2S heater low control circuit, sensor side. Refer to Circuit Testing in Wiring Systems. Does the resistance of either sensor measure above or below the specified range? | 2-50 ohms | Go to Step 13 | Go to Step 11 |
9 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 |
Inspect for poor connections 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 12 | |
11 | Inspect for poor connections at the harness connector of the affected HO2S. 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 PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
13 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 . Did you complete the replacement? | -- | Go to Step 14 | -- |
14 |
Does the DTC run and pass? | -- | Go to Step 15 | Go to Step 2 |
15 | Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
