P0131 O2 Sensor Circuit Low Voltage(Bank 1 / Sensor 1) - Automotive Repair Guides & Equipment

COMPONENT LOCATION

GENERAL DESCRIPTION

In order to control emissions of the CO, HC and NOx components of the exhaust gas, heated oxygen sensor (HO2S), mounted on the front side and rear side of catalytic converter, detects the oxygen content in the exhaust gas. The front HO2S signal is used to control air/fuel ratio (closed loop fuel control) and the rear HO2S signal is used to monitor front HO2S and catalyst for proper operation. The HO2S requires a minimum temperature to operate properly and provide a closed loop fuel control system. The HO2S contains the heater element to reduce its warming-up time and ensure its performance during all driving conditions. The oxygen sensor generates a voltage that indicates the difference between the oxygen content of the exhaust stream and the oxygen content of ambient air. When the exhaust stream is “rich,” there is more oxygen in the ambient air than in the exhaust stream, so the voltage will be higher.

DTC DESCRIPTION

Checking output signals from HO2S under detecting condition, if an output signal is below specified value for more than predeterminate time, ECM sets P0131.

DTC DETECTING CONDITION

Item

Detecting Condition

Possible Cause

DTC Strategy

Monitor signal voltage

1.	Poor connection

2.	Short to ground in harness

3.	HO2S(B1/S1)

ECM

Enable Conditions

Battery voltage ≥ 10V

Engine running ≥ 60 sec

Engine warm-up state

Threshold value

The voltage of HO2S(B1/S1) < 0.03V

Diagnosis Time

Continuous (more than 12.5 sec. failure for every 15 sec.test)

MIL On Condition

3 Driving Cycles

SPECIFICATION

A/F Ratio (λ)	Output Voltage (V)
RICH	Min. 0.8
LEAN	Max. 0.1

DIAGNOSTIC CIRCUIT DIAGRAM

SIGNAL WAVEFORM & DATA

Fig.1) Normal graph of upstream HO2S and downstream HO2S at idle.

Fig.2) Normal waveforms of upstream HO2S(the upper) and downstream HO2S(the lower) (chassis ground used)

Fig.3) Normal waveforms of upstream HO2S(the upper) and downstream HO2S(the lower) (sensor ground used)

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. And as racing, Its frequency rises.

MONITOR GDS DATA

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

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.

Is parameter displayed “Present fault”?

	▶ Go to “Terminal and Connector inspection” procedure.
	▶ Fault is intermittent caused by poor contact in the sensor’s and/or ECM’s connector or was repaired and ECM memory was not cleared. Thoroughly check connectors for looseness, poor connection, ending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary

ERMINAL AND CONNECTOR INSPECTION

1.	Many malfunctions in the electrical system are caused by poor harness and terminals. Faults can also be caused by interference from other electrical systems, and mechanical or chemical damage.

2.	Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage.

Has a problem been found?

	▶ Repair as necessary .
	▶ Go to ” Signal Circuit Inspection ” procedure.

SIGNAL CIRCUIT INSPECTION

■ Check voltage

1.	IG “OFF” and disconnect HO2S(B1/S1) connector.

IG “ON”.

Measure voltage between signal terminal of HO2S(B1/S1) harness connector and chassis ground.

Approx. 0.6~0.9V

Is the measured voltage within specification ?

	▶ Go to “Component Inspection” procedure.
	▶ Repair short to ground in harness

COMPONENT INSPECTION

■ 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 GDS. Fig.1) Normal waveforms of upstream HO2S(the upper) and downstream HO2S(the lower) (chassis ground used) Fig.2) Normal waveforms of upstream HO2S(the upper) and downstream HO2S(the lower) (sensor ground used)

Is the sensor switching properly?

	▶ Go to “Check HO2S” as below.
	▶ Substitute with a known – good HO2S and check for proper operation.

■ Check HO2S

1.	IG “OFF” and disconnect HO2S connector.

2.	Check that the HO2S is securely installed.

3.	Check the HO2S for contamination or damage

Is the sensor normal?

▶ Substitute with a known – good ECM and check for proper operation. If the problem is corrected, replace ECM.

There is a memory reset function on GDS that can erase optional parts automatically detected and memorized by ECM. Before or after testing ECM on the vehicle, use this function to reuse the ECM on the others

▶ Substitute with a known – good HO2S and check for proper operation.

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