P0131

Fix code P0131

Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 1). This sensor is located on the engine bank that houses #1 cylinder and is located BEFORE the catalytic converter

The PCM sends a reference voltage (usually 5-volts) to the variable resistor in the oxygen sensor and looks for a return voltage. Once the sensor is heated up, the PCM expects to see a varying voltage. If the PCM sees a constant low voltage, it will set a trouble code P0131.

Most common causes are: vacuum leak that’s allowing too much unmetered air into the combustion chamber and causing lean misfires, bad oxygen sensor, poor connection either at PCM or O2 sensor.

TEST: Very difficult to test without either scope or scan tool. The most effective way to determine if you have a vacuum leak is to examine the fuel trim reading on a scan tool. If you have a vacuum leak and the sensor detects a continuous lean exhaust condition, the PCM will add fuel to compensate. Fuel trim should be as low as possible, but never approaching 25%. That would indicate a vacuum leak.

To learn how to replace an oxygen sensor, click here

© 2012 Rick Muscoplat