Circuit Description
Heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias, voltage of approximately 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.
The heating elements within each HO2S heat the sensor. The powertrain control module (PCM) controls the HO2S heater control circuit. The HO2S heater diagnostic monitors the current draw through the HO2S output driver module (ODM) when the engine is running. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.
If the PCM detects that the HO2S 2 voltage has not changed more than 150 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 |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0141 HO2S Heater Performance Bank 1 Sensor 2
Conditions for Running the DTC
| • | DTCs P0036, P0137, P0138, or P0140 are not set. |
| • | DTCs P2A01, P0401, and P0420 are not commanding fuel. |
| • | The scan tool special functions are not active. |
| • | The system voltage is between 9-18 volts. |
| • | 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 26 g/s. |
| • | The HO2S 1 voltage parameter is between 400-500 mV at start-up. |
Conditions for Setting the DTC
| • | The HO2S voltage has not moved above or below bias voltage by more than 150 mV since engine start up. |
| • | The PCM detects that the HO2S 2 voltage has not moved above or below bias voltage by more than 150 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: Engine Controls Connector End Views or Powertrain Control Module Connector End Views | ||||||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||||||
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 Control Module References in Computer/Integrating Systems for replacement, setup, and programming. 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? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK | ||||||||||
