General Information

P0131 O2 Sensor Circuit Low Voltage (Bank 1 / Sensor 1)

General Information

Component Location





General Description

The HO2S (Heated Oxygen Sensor) is used to supply the PCM with information regarding the composition of the air/fuel mixture. The HO2S is positioned in the exhaust pipe ahead of the TWC. To measure the oxygen content, the HO2S requires a supply of ambient air as a reference. Since this is supplied through the wiring, the lead must not be clamped or damaged in any other way. The HO2S produces a voltage that varies between 0.1 V and 0.9 V under normal operating conditions. The Engine Control Module (PCM) monitors this voltage and determines if the exhaust gas is lean or rich. If the voltage input at the PCM is under approx. 0.45 V the exhaust is lean, and if the voltage input is over approx. 0.45 V the exhaust is rich. The PCM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary.

DTC Description

PCM sets DTC P0131 if the HO2S (B1S1) voltage remains excessively low for a predetermined time.

DTC Detecting Condition





Diagnostic Circuit Diagram





Signal Waveform & Data




> Sector A : Before Oxygen Sensor (B1S1) activated
> Sector B : Normal signal of Oxygen Sensor (B1S1) during idle
> Sector C : Line break in signal circuit