GM Service Manual Online
For 1990-2009 cars only
Table 1: P2271 HO2S Signal Stuck Rich

Circuit Description

The engine control module (ECM) supplies a voltage near 450 mV between the heated oxygen sensor (HO2S) 2 signal circuit and the low reference circuit. The HO2S varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.

    • The ECM monitors the HO2S voltage to determine if the signal voltage goes below a predetermined threshold within a certain amount of time. If the ECM determines that the signal voltage remains above a threshold, the ECM commands a lean condition. If the signal voltage does not go below the threshold within a certain amount of time after commanding the system lean, this DTC sets.
    • The ECM monitors the HO2S voltage during fuel cut-off. If the ECM determines that the signal voltage is more than a predetermined voltage during fuel cut-off, this DTC sets.

DTC Descriptors

This diagnostic procedure supports the following DTC.

DTC P2271 HO2S Signal Stuck Rich Sensor 2

Conditions for Running the DTC

    • Before the ECM can report DTC P2271 failed, DTCs P0443, P0458, and P0459 must run and pass.
    • DTCs P0036, P0037, P0038, P137, P0138, P0140, P0141, P0301-6, P0341, P0342, P0343, P0346, P0347, P0348, P0366, P0367, P0368, P0391, P0392, P0393, P0455, P0461, P0462, P0463, P0496, P2177, P2178, P2187, and P2188 are not set.
    • The engine is operating.
    • The rear HO2S is at operating temperature for more than 10 seconds.
    • The HO2S 2 is in closed loop.
    • The HO2S 2 heating is stable for more than 10 seconds.
    • The HO2S 2 is more than a calculated temperature for at least 30 seconds.
    • The calculated exhaust temperature is more than 350°C (662°F).
    • The mass air flow (MAF) sensor is between 8-33 g/s for the intrusive test.
    • The measured airflow is more than 15 g during a decel fuel cut-off.
    • DTC P2271 runs continuously once the above conditions are met.

Conditions for Setting the DTC

If the ECM detects that the rear HO2S 2 voltage is more than 740 mV for more than 100 seconds, then an intrusive test is performed. The ECM will lean the fuel mixture up to -7 percent and then wait for 10 seconds at -7 percent. If the ECM detects that the HO2S 2 voltage is still more than 740 mV, the ECM then tests the HO2S 2 at the next decel fuel cut-off. If the ECM detects the HO2S 2 voltage is more than 202 mV after 4 seconds in decel fuel cut-off, this DTC sets.

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 4 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.

Diagnostic Aids

The following table illustrates the ECM connector locations:

ECM Connector Location

C2

C1

Front of Vehicle

    • Use the J 35616 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.
    • A fuel delivery condition causes this DTC to set. Thoroughly inspect all items that cause a rich condition.
    • For an intermittent condition, refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step determines if a condition exists.

  2. This step is testing for a rear HO2S sensor circuit condition. A circuit condition sets this DTC.

  3. This step is testing for an intermittent circuit condition. Thoroughly inspect the HO2S 2 circuits for an intermittent circuit condition.

P2271 HO2S Signal Stuck Rich

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

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

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Allow the engine to reach operating temperature.
  2. Operate the vehicle within the parameters specified in Conditions for Running the DTC.
  3. Observe the diagnostic trouble code (DTC) information with a scan tool.

Did DTC P2271 fail this ignition?

--

Go to Step 4

Go to Step 3

3

  1. Observe the Freeze Frame and/or the Failure records data for this DTC.
  2. Turn the ignition OFF 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 and/or the Failure records data.

Does the DTC fail this ignition cycle?

--

Go to Step 4

Go to Diagnostic Aids

4

Is DTC  P0137, P0138, or P0140 also set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 5

5

  1. Operate the engine above 1,200 RPM for 30 seconds.
  2. Observe the HO2S 2 voltage parameter with a scan tool.

Is the voltage less than the specified value?

1,050 mV

Go to Step 8

Go to Step 6

6

  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 voltage within the specified range?

350-550 mV

Go to Step 12

Go to Step 7

7

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

Did you find and correct the condition?

--

Go to Step 17

Go to Step 13

8

Move the related HO2S 2 harnesses between the HO2S harness connector and the engine control module (ECM) while monitoring the HO2S 2 voltage parameter with a scan tool.

Does the HO2S parameter change abruptly while moving the related harnesses?

--

Go to Step 14

Go to Step 9

9

  1. Turn OFF the ignition.
  2. Disconnect the HO2S 2.
  3. Inspect the HO2S 2 for the following conditions:
  4. • For damaged wiring between the HO2S and the ECM--An intermittent circuit condition may cause this DTC to set.
    • For terminal corrosion or water intrusion in the HO2S harness connector
    • For the correct terminal tension
    • The HO2S is securely installed.
    • For any exhaust leaks--Refer to Symptoms - Engine Exhaust in Engine Exhaust.
  5. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 10

10

Inspect for the following conditions:

    • Inspect for a collapsed air intake duct.
    • Inspect for a restricted air filter element. Refer to Air Cleaner Element Replacement .
    • Inspect the mass air flow (MAF) sensor for foreign objects. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .
    • Inspect for excessive fuel in the crankcase. Change the oil as necessary.
    • Inspect for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Inspect the engine control grounds for being clean, tight, and in the correct locations.
    • Inspect for an engine mechanical condition. Refer to Symptoms - Engine Mechanical in Engine Mechanical - 3.6L (LY7).

Did you find and correct the condition?

--

Go to Step 17

Go to Step 11

11

Important: When you have completed the fuel system diagnosis, return to this diagnostic.

Test the fuel system for operating rich. Refer to Fuel System Diagnosis .

Did you find and correct the condition?

--

Go to Step 17

Go to Step 12

12

Test for shorted terminals and for poor connections at the HO2S 2. 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 17

Go to Step 15

13

Test for shorted terminals and for poor connections at the ECM. 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 17

Go to Step 16

14

Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 17

--

15

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

Did you complete the replacement?

--

Go to Step 17

--

16

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 17

--

17

  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 18

18

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK