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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2005 🢒 G6 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 DTC P2A00

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, 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.
    • 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?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Start the engine.
  2. Allow the engine to idle at operating temperature. Refer to Scan Tool Data List .
  3. Clear the DTC and record the Freeze Frame/Failure Records.
  4. Observe the affected HO2S parameter with a scan tool.

Does the voltage fluctuate rapidly above and below the specified range?

300-600 mV

Go to Step 3

Go to Step 4

3
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Testing for Intermittent Conditions and Poor Connections

4
  1. Turn OFF the ignition.
  2. Disconnect the affected heated oxygen sensor (HO2S) 1.
  3. Connect a 3-amp fused jumper wire between the HO2S 1 high signal circuit on the engine harness side and a good ground.
  4. Turn ON the ignition, with the engine OFF.
  5. Observe the affected HO2S parameter with a scan tool.

Is the voltage less than the specified value?

15 mV

Go to Step 5

Go to Step 6

5
  1. Remove the jumper wire from the previous step.
  2. Connect a 3-amp fused jumper wire between the high signal circuit and the low signal circuit of the HO2S 1 on the engine harness side.
  3. Observe the affected HO2S parameter with a scan tool.

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 Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs .

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 Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs .

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.

    • HO2S contamination

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

    • Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring
    • Exhaust system leaks or restrictions
    • Evaporative emission (EVAP) system malfunction--Inspect the EVAP control system. Refer to Inspection/Maintenance (I/M) System Check .
    • Incorrect fuel pressure--Refer to Fuel System Diagnosis .

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 Testing for Intermittent Conditions and Poor Connections , Connector Repairs , and Heated Oxygen Sensor Wiring Repairs .

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 Replacement - Bank 1 Sensor 1 .

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
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

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?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK