Fuel System > Engine Control System > P2271 O2 Sensor Signal Stuck Rich (Bank 1 Sensor 2)

Component Location

General Description

The rear heated oxygen sensor is mounted on the rear side of the Catalytic Converter (warm-up catalytic converter) or in the rear exhaust pipe, which is able to detect catalyst efficiency. The rear heated oxygen sensor (HO2S) produces a voltage between 0V and 1V. This rear heated oxygen sensor is used to estimate the oxygen storage capability. If a catalyst has good conversion properties, the oxygen fluctuations are smoothed by the oxygen storage capacity of the catalyst. If the conversion provided by the catalyst is low due to aging, poisoning or misfiring, then the oxygen fluctuations are similar to signals from the front oxygen sensor.

DTC Description

Checking output signals from HO2S under detecting condition, if HO2S's signal is rich during fuel cut-off conditions, PCM sets P2271. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycles.

DTC Detecting Condition

Item

Detecting Condition

Possible cause

DTC Strategy

•	Monitor HO2S's signal

•	Poor Connection

•	Faulty HO2S

•	Faulty PCM

EnableConditions

•	Battery voltage ≥ 10V

•	Engine running ≥ 60sec.

•	Power Enrichment conditions

•	Engine warm-up state

•	Not in Transient Conditions

Threshold value

•	HO2S's signal > 0.42V

DiagnosisTime

•	Continuous (More than 8 sec. failure for every 9 sec. Test)

MIL On Condition

•	2 Driving Cycles

Specification

Test Condition	HO2S Voltage(Sensor1)	HO2S Voltage(Sensor2)
HO2S Signal at idle after warm-up	Signal is normally switching from rich to lean more than 3 times in 10 sec.	Signal is normally above 0.6V.
HO2S signal at open circuit(Pumping current OFF)	Approx. 0.45V
HO2S signal at open circuit(Pumping current ON)	Approx. 3.5V

Schematic Diagram

Signal Wavefrom And Data

After warming-up, if accelerator pedal is released suddenly around 4000rpm, the HO2S signal reading will be lower than 200mV resulting from Fuel cut-off for the moment. Conversely, if suddenly accelerator pedal is depressed, HO2S signal reading will be around 0.6V ~1.0V. At idle, Normally HO2S signal will switch from lean to rich with 3 Hz. At higher engine RPM, the switching frequency increases.

Monitor DTC Status

Check DTC Status

(1)	Connect scantool to Data Link Connector(DLC).

(2)

IG "ON".

(3)	Select "DTC" button, and then Press "DTC Status" to check DTC's information from the DTCs menu.

(4)	Read "DTC Status" parameter.

(5)

Is parameter displayed "Present fault"?

	▶ Go to "Component Inspection" procedure.
	▶ Fault is intermittent caused by poor contact in the sensor's and/or PCM's connector or was repaired and PCM memory was not cleared. Thoroughly check connectors for looseness, poor connection, ending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure.

Component Inspection

Check the condition of HO2S

(1)	Check HO2S for poor connection or loose terminal.

(2)	Check if HO2S is ensurely installed.

(3)

Are the conditions of HO2S normal ?

	▶ Go to "Check the Signal waveform of HO2S" as follows.
	▶ Repair it and then go to "Verification of Vehicle Repair" procedure.

Check the Signal waveform of HO2S

(1)	IG "OFF" and connect HO2S connector.

(2)	Engine start.

(3)	After warming-up, monitor signal waveform of HO2S with scantool.

(4)

Is the sensor switching properly?

	▶ Substitude with a known-good PCM and check for proper operation. If the problem is corrected, replace PCM and go to "Verification of Vehicle Repair" procedure.
	▶ Substitute with a known - good HO2S and check for proper operation. If the problem is corrected, go to "Verification of Vehicle Repair" procedure.

There is a memory reset function on scantool that can erase optional parts automaticallydetected and memorized by PCM. Before or after testing PCM on the vehicle, use this function before reusing the PCM

Verification Of Vehicle Repair

After a repair, it is essential to verify that the fault has been corrected.

1.	Connect scantool and select "DTC" button.

2.	Press "DTC Status" button and confirm that "DTC Readiness Flag" indicates "Completed". If not, drive the vehicle within conditions noted in the freeze frame data or enable conditions

3.	Read "DTC Status" parameter

Is parameter displayed "History(Not Present) fault"?

	▶ System performing to specification at this time. Clear the DTC
	▶ Go to the applicable troubleshooting procedure.