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 0-1,100 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 1,100 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. This allows the system to enter Closed Loop earlier and the control module to calculate air-to-fuel ratio quicker.
If the powertrain control module (PCM) detects an active HO2S 1 signal of a lower than calibrated minimum amplitude, DTC P2A00 will set.
The HO2S 1 has the following circuits:
| • | A HO2S 1 high signal circuit |
| • | A HO2S 1 low signal circuit |
| • | A HO2S 1 heater ignition voltage circuit |
| • | A HO2S 1 heater low control circuit |
DTC Descriptor
This diagnostic procedure support the following DTC:
DTC P2A00 HO2S Circuit Closed Loop (CL) Performance Bank 1 Sensor 1
Conditions for Running the DTC
The following conditions must be met:
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0131, P0132, P0133, P0134, P0135, P0201, P0202, P0203, P0204, P0205, P0206, P0420, P0443, P0446, P0449, P0452, P0453, P0455, P0496, P1133, P1134 are not set. |
| • | The Engine Run Time parameter is at least 3 minutes. |
| • | The MAF sensor parameter is between 5-38 g/s. |
| • | The Engine Speed parameter is between 602-3,000 RPM. |
| • | The TP sensor parameter is between 3-35 percent. |
| • | The ECT sensor parameter is more than 65°C (149°F). |
| • | The system voltage is between 9-18 volts. |
| • | Traction control, if equipped, is not active. |
| • | Decel Fuel Cutoff parameter is Not Active. |
| • | Power Enrichment (PE) parameter is Not Active. |
| • | The Catalytic Converter Protection Active parameter is NO. |
| • | The predicted oxygen sensor temperature is more than 0°C (32°F). |
| • | The above conditions have been met for at least 3 seconds. |
Conditions for Setting the DTC
| • | The PCM detects HO2S 1 voltage signal remains within 300-600 mV range for more than 3.6 seconds. |
| • | This diagnostic runs continuously. |
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 | |||||||||||||
2 |
Does the HO2S 1 voltage fluctuate rapidly above and below the specified range? | 300-600 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 HO2S 1 voltage within the specified range? | 425-500 mV | Go to Step 5 | Go to Step 6 | ||||||||||||
5 |
Is the HO2S 1 voltage less than the specified value? | 25 mV | Go to Step 7 | Go to Step 6 | ||||||||||||
6 |
Is the resistance of each circuit less than the specified value? | 5 ohms | Go to Step 10 | Go to Step 11 | ||||||||||||
7 |
Does the test lamp illuminate? | -- | Go to Step 8 | Go to Step 4 in DTC P0135 | ||||||||||||
8 | 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 14 | Go to Step 9 | ||||||||||||
9 | Test for an intermittent and for a poor connection at the harness connector of the HO2S 1. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 12 | ||||||||||||
10 | 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 . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 | ||||||||||||
11 | Repair the open or high resistance on the affected circuit. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 14 | -- | ||||||||||||
12 | Replace the HO2S 1 sensor. Refer to Heated Oxygen Sensor 1 Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||||||||
13 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||||||||
14 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 15 | ||||||||||||
15 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||||
