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 provide an accurate voltage signal. If the PCM detects an active HO2S 1 signal of a lower than calibrated minimum amplitude, DTC P2A00 will set for bank 1 sensor 1.
Each HO2S 1 has the following circuits:
| • | The HO2S 1 high signal circuit |
| • | The HO2S 1 low signal circuit |
| • | The HO2S 1 ignition 1 voltage circuit |
| • | The HO2S 1 heater low control circuit |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P2A00 HO2S Circuit Closed Loop (CL) Performance Bank 1 Sensor 1
Conditions for Running the DTC
| • | DTCs P0030, P0053, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0125 where applicable, P0128, P0131, P0132, P0133, P0134, P0135, P0201, P0202, P0203, P0204, P0205, P0206, P0220, P0442, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0464, P0496, P1133, P1134, P2135 are not set. |
| • | Where applicable, DTCs P0412, P2440, P2444 are not set. |
| • | The Engine Run Time parameter is at least 3 minutes. |
| • | The traction control, if equipped, is not active. |
| • | The PCM is not commanding Power Enrichment or Decel Fuel Cutoff modes. |
| • | The MAF Sensor parameter is between 8-38 g/s. |
| • | The Engine Speed parameter is between 602-3,000 RPM. |
| • | The TP Indicated Angle 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. |
| • | The above conditions have been met for 3 seconds. |
Conditions for Setting the DTC
| • | The PCM detects that the loop status parameter is open. |
| • | DTC P2A00 sets within 50 seconds, when the above condition is met. |
| • | 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: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||||||
2 |
Does the 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 Testing for Intermittent Conditions and Poor Connections | ||||||||||
4 |
Is the voltage less than the specified value? | 15 mV | Go to Step 5 | Go to Step 6 | ||||||||||
5 |
Is the voltage less than the specified value? | 15 mV | Go to Step 8 | Go to Step 7 | ||||||||||
6 | Test the HO2S 1 high signal circuit for an open or high resistance. Refer to the following: Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | ||||||||||
7 | Test the HO2S 1 low signal circuit for an open or high resistance. Refer to the following: Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | ||||||||||
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 13 | Go to Step 9 | ||||||||||
9 |
Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section. Test for an intermittent and for a poor connection at the HO2S 1. Refer to the following Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11 | ||||||||||
10 | Test for an intermittent and for a poor connection at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 | ||||||||||
11 |
Notice: Refer to Heated Oxygen Sensor Resistance Learn Reset Notice in the Preface section. Replace the HO2S 1. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||||
12 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||||
13 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 14 | ||||||||||
14 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||
