For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC P2271: HO2S Signal Stuck Rich Sensor 2

### Circuit/System 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.

This DTC determines if the rear HO2S is stuck in a normal rich voltage range. The ECM enables deceleration fuel cut-off (DFCO) for this intrusive test. The ECM monitors the HO2S 2 voltage while in DFCO. If the ECM detects the HO2S 2 voltage does not achieve a lean threshold voltage, this DTC sets.

### Conditions for Running the DTC

• | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0114, P0116, P0117, P0118, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0301, P0302, P0303, P0304, P1516, P2101, P2119, or P2176 are not set.

• | The ignition voltage is between 10-18 volts.

• | The engine run time is greater than 225 seconds.

• | The engine speed is between 1,100-3,250 RPM.

• | The airflow into the engine is between 0-25 g/s.

• | The vehicle speed is between 45-129 km/h (28-80 mph).

• | The fuel level is greater than 10 percent.

• | The engine is operating in closed loop.

• | The HO2S heater is commanded ON for greater than 80 seconds.

• | The calculated catalytic converter temperature is between 450-1,000°C (842-1,832°F).

• | Decel fuel cut-off (DFCO) is enabled

• | DTC P2271 runs once per ignition cycle when the above conditions are met for greater than 1 second.

### Conditions for Setting the DTC

The ECM detects that the rear HO2S voltage is greater than 150 mV while the intrusive test is performed.

### Action Taken When the DTC Sets

DTC P2271 is a Type B DTC.

### Conditions for Clearing the DTC

DTC P2271 is a Type B DTC.

### Diagnostic Aids

#### HO2S Terminal Identification

Lock Tab
1 | 2
3 | 4

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. DTC P0036, P0054, P0137, P0138, P0140, or P0141 should not be set.

⇒ | If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. Ignition OFF for 2 minutes. Ignition ON, engine OFF, observe the scan tool HO2S 2 voltage parameter. The reading should be 1275 mV.

Note:

• | The HO2S voltage will increase to greater than 100 mV as sensor temperature increases.

• | This procedure must be performed within 10 seconds after the engine is started.

3. Engine idling, increase engine speed to 3000 RPM, observe the scan tool HO2S 2 voltage parameter. The reading should decrease from 1275 mV to less than 100 mV.
4. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

1. Engine idling, move the HO2S 2 harness connector and the engine control module (ECM) harness connector while monitoring the HO2S 2 voltage parameter. Verify that the HO2S parameter does not change abruptly while moving the related harnesses.

⇒ | If the HO2S parameter does change abruptly while moving the related harnesses repair the circuit as necessary.

2. Ignition OFF, disconnect the harness connector at the HO2S 2.
3. Ignition OFF for 1 minute, test for less than 5 Ω between the low reference circuit terminal 3 and ground.

⇒ | If greater than the specified range, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

4. Ignition ON, test for 1.5-2.1 V between the signal circuit terminal 1 and ground.

⇒ | If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

5. Install a 3 A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 3. Engine running, verify the scan tool HO2S parameter is less than 60 mV.

⇒ | If greater than the specified value, replace the ECM.

6. Verify none of the following conditions exist:

• | Rich fuel injectors--Refer to Fuel Injector Balance Test with Special Tool.

• | Water intrusion in the HO2S harness connector

• | High fuel system pressure--Refer to Fuel System Diagnosis.

• | Fuel that is contaminated--Refer to Alcohol/Contaminants-in-Fuel Diagnosis.

• | Fuel saturation of the evaporative emission (EVAP) canister

⇒ | If you find any of the above conditions, repair as necessary.

7. If all circuits test normal, test or replace the HO2S 2.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Caution: When replacing the HO2S perform the following:

• | A code clear with a scan tool, regardless of whether or not a DTC is set

• | HO2S heater resistance learn reset with a scan tool, where available

Perform the above in order to reset the HO2S resistance learned value and avoid possible HO2S failure.

• | Heated Oxygen Sensor 2 Replacement

• | Control Module References for ECM replacement, setup, and programming