Error code P0131 is described as O2 Sensor Circuit Low Voltage Bank 1 Sensor 1. This indicates there is a problem in the wiring, such as corrosion, breaks or separation. The O2 Sensor could be non functioning, or there could be a bad connection to the ECU, or it is possible that the power source is not supplying enough voltage to the sensor.


The O2 Sensor is positioned in the exhaust system to monitor oxygen levels in the exhaust gases that exit the engine. This gauges fuel burning efficiency as well as checks that the engine is maintaining the proper fuel/air ratio for a clean burn. This helps the ECU determine if the fuel mixture is rich (less oxygen) or lean (more oxygen).

Common Symptoms

  • Vehicle runs less efficiently
  • Low voltage
  • Bad fuel/air mixture
  • Poor idle
  • Missing at steady throttle
  • Hard starting
  • Fuel economy suffering

Possible Causes

  • Oxygen Sensor itself could be bad
  • Voltage could be insufficient
  • Connection to the oxygen sensor could be bad
  • Break in a wire or wires could have occurred
  • Insulation of the wire may have worn and corroded
  • Possible short to ground in the wire

How To Check

In order to check the O2 Sensor, utilize an OBD II scanner to determine the error code. If the scanner shows the P0131 code, then this means that the number one oxygen sensor on Bank 1 is faulty.

  • Vacuum Lines
  • Check all vacuum lines for leaks, cracks, or unplugged hoses.
  • Fouling
  • Check oxygen sensor for fouling from gasoline additives or oil from worn engines.
  • Exhaust Leaks
  • Check for holes in the exhaust system and visually inspect from the exhaust manifold gasket back to the tailpipe.
  • Electrical Connections
  • Visually check electrical connections from the ECU and in the vicinity of the O2 Sensor.
  • Check for proper operation of oxygen sensors by checking resistance with a Volt Ohm meter.

How To Fix

Unbolt the two bolts that hold the O2 Sensor in place and remove the sensor to check for fouling. If the sensor is fouled, remove it and place it in a small can that has a lid; pour gasoline on top of the sensor until it is submerged. Once the sensor is submerged, place the lid on the can and gently swirl it around to clean the sensor. Allow it to set and soak overnight. The following day remove and dislodge any loose particles with a soft bristle brush. Rinse the sensor in the gasoline once more and then remove it to air dry before remounting it. If this procedure does not solve the problem, replace it with a new O2 Sensor. (This option is the last check in the sequence, because at this point, the sensor can easily be replaced if it is not fouled.)

Once the repairs or replacement have been made, clear the codes from the ECU/ECM and test drive at about 30-35 miles per hour for one to two miles.

For more information about various OBD II codes, browse the website. If professional assistance is required, feel free to contact us