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DTC P2271 (Without LF1)

DTC P2271 (Without LF1)

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 Descriptor

DTC P2271

HO2S Signal Stuck Rich Sensor 2

Circuit Description

The engine control module (ECM) supplies a voltage near 450 mV between the heated oxygen sensor (HO2S) 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 and stores the HO2S voltage information. The ECM evaluates the HO2S voltage samples in order to determine the amount of time that the HO2S voltage was out of range. The ECM compares the stored HO2S voltage samples taken within each sample period and determines if the majority of the samples are out of the operating range. The ECM evaluates if the following occurs:


• 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 the threshold, the ECM will command the fuel system lean to determine if the HO2S signal voltage can be forced below the threshold within a certain amount of time.

• The ECM monitors the HO2S voltage during fuel cut-off to determine if the signal voltage is greater than a predetermined threshold.


Conditions for Running the DTC


• Before the ECM can report DTC P2270 failed, DTCs P0036, P0037, P0038, P0137, P0138, P0140, P0141, P0341, P0342, P0343, P0346, P0347, P0348, P0366, P0367, P0368, P0391, P0392, P0393, P0443, P0458, and P0459 must run and pass.

• DTC P0461, P0462, P0463, P2066, P2067, or P2068 is not set.

• The engine is operating.

• The ignition voltage is greater than 10 V.

• The rear HO2S are at operating temperature for greater than 10 s.

• The fuel injectors are enabled.

• The long term fuel control is enabled.

• The mass air flow sensor is greater than 10 g/s.

• The MAF sensor is between 6-33 g/s for greater than 3 s during the intrusive test.

• The accumulated air flow into the engine is greater than 15 g during the fuel cut-off event.

• DTC P2271 runs continuously when the above conditions are met.


Conditions for Setting the DTC

The ECM detects that the rear HO2S voltage is less than 650 mV for greater than 100 s, then an intrusive test is performed. The ECM downblends the fuel mixture by up to -7 % and then waits 10 seconds at -7 %. If the ECM detects that the HO2S voltage is still greater than 650 mV, the ECM evaluates the HO2S at the next fuel cut-off during engine braking. The diagnostic trouble code is activated if the ECM detects that the HO2S voltage is greater than 200 mV after 4 s or a cumulative 30 s at fuel cut-off during engine braking.

Action Taken when the DTC Sets

DTC P2271 is a Type B DTC.

Conditions for Clearing the MIL/DTC

DTC P2271 is a Type B DTC.

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. Verify that DTC P0137, P0138, or P0140 is not set.

2. If any of the DTCs listed are set refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

3. Operate the engine above 1,200 RPM for 30 s, observe the HO2S 2 voltage parameter. The reading should fluctuate above and below the range of 350-550 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 operating, move the related HO2S harness between the B52 HO2S harness connector and the K20 ECM while monitoring the HO2S 2 voltage parameter. Verify that the HO2S 2 parameter does not change abruptly while moving the related harnesses.

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

3. Ignition OFF, disconnect the harness connector at the B52 HO2S 2.

4. Ignition ON, verify that the HO2S parameter is between 350-500 mV.

5. If greater than 500 mV, test the signal circuit terminal 4 for a short to voltage. If the circuit/connections test normal, replace the K20 ECM.

6. Verify none of the following conditions exist:

• Rich fuel injectors-Refer to Fuel Injector Solenoid Coil Test .

• 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 .

• A collapsed air intake duct

• A restricted air filter element

• Exhaust system restrictions

• Excessive fuel in the crankcase

• An engine mechanical condition-Refer to Symptoms - Engine Mechanical .

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

7. If all circuits/connections test normal, replace the B52 HO2S 2.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Heated Oxygen Sensor Replacement - Sensor 2

• Control Module References for Engine Control Module replacement, setup, and programming