Circuit Description
The heated oxygen sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with signal high and low circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.
The HO2S contains a heater that is necessary in order to quickly warm the sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When thee HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors the HO2S signal voltage for Closed Loop fuel control During normal Closed Loop fuel control operation, the control module will add fuel, or enrich the mixture, when the HO2S detects a lean exhaust content. The control module will subtract fuel, or "lean out" the mixture, when the HO2S detects a rich exhaust condition. Certain vehicle models utilize an oxygen sensor behind the catalytic converter in order to monitor the catalyst efficiency.
The PCM runs the heater test only on a cold start (depends on the cumulative air flow) and only once an ignition cycle. When you start the engine the PCM monitors the HO2S voltage. When the HO2S voltage goes above or below the bias range threshold, the PCM determines how much time was taken. If the PCM detects that the process took too much time for the HO2S to enter into normal operating range, a diagnostic trouble code (DTC) sets. The time the process takes the HO2S to reach operating temperature is based on the amount of air that flows into the engine.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0125, P0128, P0200, P0300, P0351-P0358, P0401, P0404, P0405, P0410, P0418, P0443, P0446, P0449, P1120, P1220, P1221, P1258, or P1404 are not set. |
| • | The secondary air injection (AIR) and the exhaust gas recirculation (EGR) diagnostics are not active. |
| • | The IAT and the 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 average airflow is below 22 g/s. |
| • | The HO2S voltage is between 425-475 mV at engine start-up. |
| • | The scan tool must be disconnected. |
Conditions for Setting the DTC
The HO2S voltage remains between 300-600 mV for a predetermined time, depending on the ECT and the air flow.
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
| • | The heater diagnostic will only run on a cold start and will run once per ignition cycle. |
| • | An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and connections for breaks or contamination. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. |
| • | Use the Freeze Frame/Failure Records data in order to locate an intermittent condition in the following ways: |
| - | If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in determining how many miles since the DTC set. |
| - | The Fail Counter and Pass Counter can also aid in determining how many ignition cycles the diagnostic reported a pass or a fail. |
| - | Operate the vehicle within the same Freeze Frame conditions that you observed in order to isolate when the DTC failed. Use the following conditions for your tests: |
| • | The RPM |
| • | The load |
| • | The vehicle speed |
| • | The temperature |
| - | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests whether an ignition 1 voltage supply is available at the sensor.
-
This step tests whether a ground is available at the sensor.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics | |||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |
2 |
Does DTC P0141 fail this ignition? | Go to Step 3 | Go to Diagnostic Aids |
3 | Inspect the HO2S fuse for an open. Is the HO2S fuse open? | Go to Step 10 | Go to Step 4 |
Does the test lamp illuminate? | Go to Step 5 | Go to Step 6 | |
Connect the test lamp between the HO2S ignition 1 voltage circuit and the HO2S heater low control circuit. Does the test lamp illuminate? | Go to Step 8 | Go to Step 7 | |
6 | Repair the open in the HO2S ignition 1 voltage circuit to the HO2S. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 13 | -- |
7 | Test the HO2S heater low control circuit for an open or high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 11 |
8 |
Did you find and correct the condition? | Go to Step 13 | Go to Step 9 |
9 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 . Did you complete the replacement? | Go to Step 13 | -- |
10 |
Did you complete the repair? | Go to Step 13 | -- |
11 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 12 |
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 | Use a scan tool in order to observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | System OK | |
