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 supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The PCM controls the HO2S 2 heater low control circuit with a low side driver. The HO2S 2 heater diagnostic monitors the amount of time it takes for the HO2S 2 to generate a voltage that is higher or lower than bias voltage by a calibrated amount. If the PCM detects that the HO2S 2 voltage has not changed more than 74 mV from bias voltage within a calibrated amount of time, DTC P0141 will set.
Each HO2S 2 has the following circuits:
| • | An HO2S 2 high signal circuit |
| • | An HO2S 2 low reference circuit |
| • | An HO2S 2 heater ignition voltage circuit |
| • | An HO2S 2 heater low control circuit |
| • | An HO2S low reference circuit |
Conditions for Running the DTC
| • | DTCs P0036, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0137, P0138, P0140, P0201, P0202, P0203, P0204, P0205, P0206, P0442, P0443, P0446, P0449, P0455, P0496 are not set. |
| • | The Start Up ECT parameter is less than 35°C (95°F). |
| • | The Start Up IAT parameter is less than 35°C (95°F). |
| • | The difference between the Start Up ECT parameter and the Start Up IAT parameter is less than 6°C (11°F). |
| • | The MAF Sensor parameter averages less than 23 g/s. |
| • | The HO2S 1 voltage parameter is between 400-500 mV at start-up. |
| • | The system voltage is between 9-18 volts. |
Conditions for Setting the DTC
The PCM detects that the HO2S 2 voltage has not moved above or below bias voltage by more than 74 mV within a calibrated amount of time.
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. |
Step | Action | Values | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||
2 |
Does the voltage fluctuate above and below the specified range? | 390-520 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 voltage less then the specified value? | 50 mV | Go to Step 9 | Go to Step 5 | ||||||||||
5 |
Important: Use a known good ground. DO NOT use the HO2S 2 heater low control circuit or the HO2S 2 low signal circuit. Probe the HO2S 2 heater ignition voltage circuit with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors in Wiring Systems. Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 6 | ||||||||||
6 | Inspect the HO2S 2 heater ignition voltage fuse for an open. Is the fuse open? | -- | Go to Step 10 | Go to Step 16 | ||||||||||
7 |
Is the voltage less than the specified value? | 15 mV | Go to Step 8 | Go to Step 12 | ||||||||||
8 |
Is the resistance of either circuit more than the specified value? | 5 ohms | Go to Step 17 | Go to Step 13 | ||||||||||
9 | Test the HO2S 2 high signal circuit for a short to the HO2S 2 heater low control circuit. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 15 | ||||||||||
10 | Test the HO2S 2 heater ignition voltage circuit for a short to ground and replace the fuse. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 11 | ||||||||||
11 | Test the HO2S 2 heater ignition voltage circuit on the sensor side of the HO2S connector for a short to ground. Refer to Circuit Testing in Wiring Systems. Is the sensor shorted to ground? | -- | Go to Step 18 | Go to Intermittent Conditions | ||||||||||
12 | Test the HO2S 2 high signal circuit for an open or high resistance condition. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 15 | ||||||||||
13 | Inspect for the following that may affect the HO2S operation: Notice: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in the Preface section.
Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.
Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 14 | ||||||||||
14 | Test for an intermittent and for a poor connection at the harness connector of the HO2S 2. Refer to Testing for Intermittent Conditions and Poor Connections , Connector Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 18 | ||||||||||
15 | Test for an intermittent and for a poor connection 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 20 | Go to Step 19 | ||||||||||
16 | Repair the open or high resistance condition in the HO2S 2 heater ignition voltage circuit. Refer to Wiring Repairs and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 20 | -- | ||||||||||
17 | Repair the circuit that measures high resistance. Refer to Wiring Repairs and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 20 | -- | ||||||||||
18 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 20 | -- | ||||||||||
19 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 20 | Go to Step 2 | ||||||||||
20 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 21 | ||||||||||
21 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||
