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 detects that the rear HO2S voltage is less than 650 mV for more 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 50 seconds, the DTC sets.

DTCs P2270 and P2272 are Type B DTCs.

DTCs P2270 and P2272 are Type B DTCs.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

1. Ignition ON, observe the DTC information with a scan tool. Verify that DTCs P0137, P0138, P0140, P0157, P0158, or P0160 are not set.

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

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. If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

1. Engine operating, move the related HO2S harnesses for the appropriate rear sensor between the HO2S harness connector and the engine control module (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 350 mV, test the signal circuit of the HO2S sensor 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 Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 .

•	Water intrusion in the HO2S harness connector

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

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.