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 P2270: O2 Sensor Lean/Rich Switch Signal Malfunction (Bank 1 Sensor 2)
DTC P2272: O2 Sensor Lean/Rich Switch Signal Malfunction (Bank 2 Sensor 2)

### Circuit Description

The engine control module (ECM) supplies a voltage near 450 mV between the heated oxygen sensor (HO2S) high 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 test for the following conditions:

• | The ECM monitors the HO2S voltage to determine if the signal voltage goes above a predetermined threshold within a certain amount of time. If the ECM determines that the signal voltage remains below a threshold, the ECM will command the fuel system rich to determine if the HO2S signal voltage can be forced above the threshold within a certain amount of time.

• | The ECM monitors the HO2S voltage during power enrichment to ensure that the signal voltage goes above a predetermined threshold during power enrichment.

### Conditions for Running the DTC

• | Before the ECM can report DTC P2270 or P2272 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 volts.

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

• | The long term fuel control is enabled.

• | The mass air flow (MAF) sensor is greater than 10 g/s.

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

• | DTC P2270 and P2272 runs continuously once the above conditions are met for approximately 10 minutes when the fuel level is greater than 12 percent.

• | DTC P2270 and P2272 runs continuously once the above conditions are met for approximately 20 minutes when the fuel level is less 12 percent.

### Conditions for Setting the DTC

The ECM detects that the rear HO2S voltage is less than 650 mV for greater than 100 seconds, then an intrusive test is performed. The ECM will enrich the fuel mixture up to 30 percent and then wait for 10 seconds at 30 percent. The ECM detects that the HO2S voltage is less than 650 mV during the intrusive test for greater than 4 seconds or for a cumulative of 30 seconds, the DTC sets.

### Action Taken when the DTC Sets

DTC P2270 and P2272 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTC P2270 and P2272 are Type B DTCs.

### 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.

⇒ | If any of the listed DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. Operate the engine above 1,200 RPM for 30 seconds, observe the HO2S voltage parameter. The reading should fluctuate above and below the range of 350-550 mV.
3. 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 harnesses for the appropriate rear sensor between the HO2S harness connector and the ECM, while monitoring the appropriate HO2S 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 of the appropriate HO2S.
3. Ignition ON, verify that the HO2S parameter is between 350-500 mV.

⇒ | If less than the specified range, test the signal circuit terminal 4 for a short to ground. If the circuit/connections test normal, replace the ECM.

4. Verify that none of the following conditions exist:

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

• | Water intrusion in the HO2S harness connector.

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

• | The vacuum hoses for splits, kinks and proper connection.

• | The air intake system after the mass air flow (MAF) sensor for vacuum leaks.

• | Exhaust system leaks.

• | Contaminated HO2S - Silicon.

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

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

5. If all circuits/connections test normal, replace the applicable HO2S.

### Repair Instructions

Perform the Diagnostic Repair Verification.

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 2

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 2

• | Engine Control Module Replacement for engine control module replacement, setup, and programming.