GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2007 🢒 VUE - FWD 🢒 DTC 🢒 DTC P2A01

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 in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The engine control module (ECM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started, the ECM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream.

The HO2S 2 is used for catalyst monitoring. This diagnostic runs once per ignition cycle. This diagnostic consists of two tests, a passive test and an intrusive test. During the passive test, if the HO2S 2 voltage transitions below 300 mV and above 725 mV, the DTC will pass for this ignition cycle. If the DTC does not pass during the passive test, the intrusive test will begin. During the intrusive test, the control module will force the air-to-fuel ratio rich and/or lean. The control module then waits for a predicted response from the HO2S. If the HO2S voltage transitions below 300 mV and/or above 725 mV, the DTC will pass for this ignition cycle. If the control module does not receive the expected response from the HO2S, DTC P2A01 will set .

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P2A01 HO2S Circuit Sensor 2

Conditions for Running the DTC

DTCs P0068, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0137, P0138, P0140, P0141, P0171, P0201-P0204, P0220, P0300, P0315, P0336, P0442, P0446, P0452, P0453, P0455, P0496, P0506, P0507, P0601, P0602, P0604, P0606, P0641, P0651, P1134, P1516, P1621, P1680, P1681, P2101, P2120, P2125, P2135, P2138, P2176 are not set.

Passive Test

    • The engine is running.
    • The Engine Run Time parameter is less than 13.3 minutes.

Intrusive Test

    • The Engine Run Time parameter is more than 13.3 minutes.
    • The ignition 1 Signal parameter is between 11-18 volts.
    • The Engine Speed parameter is between 1,000-5,000 RPM.
    • The Vehicle Speed parameter is between 32-128 km/h (20-80 mph).
    • The Short Term FT parameter is between -10 and +10 percent.
    • The Air Flow Calculated parameter is between 14-100 g/s.
    • The maximum number of intrusive attempts is less than 25.
    • DTC P2A01 runs continuously when the above conditions have been met for one second.

Conditions for Setting the DTC
  1. The ECM detects that the HO2S 2 did not transition below 300 mV and above 725 mV during the passive test.
  2. One of the following tests fail:
    3. • The lean intrusive test
       - The ECM detects that the HO2S 2 is more than 300 mV for 12 seconds.
       - The HO2S 1 is less than 300 mV.
       - OR
    • The rich intrusive test
       - The ECM detects that the HO2S 2 is less than 725 mV for 12 seconds.
       - The HO2S 1 is more than 600 mV.

DTC P2A01 sets within 60 seconds when the above conditions are met.

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.

Test Description

The number below refers to the step number on the diagnostic table.

  1. If the voltage does not change more that the specified value, the condition is present.

Step

Action

Value(s)

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Start the engine.
  2. Allow the engine to reach operating temperature. Refer to Scan Tool Data List .
  3. Operate the engine at 1,500 RPM for 30 seconds.
  4. While observing the HO2S 2 voltage parameter with a scan tool, quickly cycle the throttle from closed throttle to wide open throttle, 3 times.

Did the HO2S 2 voltage parameter change more than the specified value?

200 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 Intermittent Conditions

4
  1. Turn OFF the ignition.
  2. Disconnect the heated oxygen sensor (HO2S) 2.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the HO2S 2 voltage parameter with a scan tool.

Is the HO2S 2 voltage parameter less than the specified value?

100 mV

Go to Step 6

Go to Step 5

5

Observe the HO2S 2 voltage parameter with a scan tool.

Is the HO2S 2 voltage parameter more than the specified value?

800 mV

Go to Step 7

Go to Step 8

6

Test the HO2S 2 high signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 9

7

Important: The sensor may be damaged if the circuit is shorted to a voltage source.

Test the HO2S 2 high signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

8

Measure the voltage from the low signal circuit of the HO2S 2 harness connector on the engine harness side to a good ground with a DMM. Refer to Circuit Testing .

Is the voltage more than the specified value?

2 V

Go to Step 10

Go to Step 11

9

Test the HO2S 2 high signal circuit for a short to the HO2S 2 low signal circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

10

Test the HO2S 2 low signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

11
  1. Connect a 3-amp fused jumper wire between the high signal circuit of the HO2S 2 harness connector on the engine harness side and a good ground.
  2. Observe the HO2S 2 voltage parameter with a scan tool.

Is the HO2S 2 voltage parameter less than the specified value?

100 mV

Go to Step 12

Go to Step 14

12
  1. Remove the jumper wire from the previous step.
  2. Connect a 3-amp fused jumper wire between the high signal circuit of the HO2S 2 harness connector on the engine harness side and the low signal circuit of the HO2S 2 harness connector on the engine harness side.
  3. Observe the HO2S 2 voltage parameter with a scan tool.

Is the HO2S 2 voltage parameter less than the specified value?

100 mV

Go to Step 15

Go to Step 13

13

Test the HO2S 2 low signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

14

Test the HO2S 2 high signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

15

Test the HO2S 2 heater low control circuit for a short to the HO2S 2 high signal circuit or HO2S 2 low signal circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 16

16
  1. The HO2S 2 may be detecting a rich exhaust condition, a lean exhaust condition, or the HO2S may be contaminated. Inspect for the following conditions:

    2. Notice: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in the Preface section.

    • A silicon contaminated HO2S 2
    • Any water intrusion into the HO2S 2 connector
    • An exhaust leak between the HO2S 2 and the engine
    • Any vacuum leaks
    • Engine oil contaminated with fuel
    • An incorrect fuel pressure--Refer to Fuel System Diagnosis .
    • Any lean or rich fuel injectors--Refer to Fuel Injector Diagnosis .
  2. Repair any of the above or similar engine conditions as necessary.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

17

Test for shorted terminals and for poor connections at the HO2S 2. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 19

18

Test for shorted terminals and for poor connections at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 20

19

Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement .

Did you complete the replacement?

--

Go to Step 21

--

20

Replace the ECM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 21

--

21
  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 22

22

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