Powertrain, generic · Fuel and air metering

P0131 O2 Sensor Circuit Low Voltage Bank 1 Sensor 1

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

The oxygen sensor before the catalytic converter on bank 1 (sensor 1) is the main control sensor for the mixture. It is either a switching sensor (about 0.1 V lean to 0.9 V rich) or a wide-band sensor that works with a pump current evaluated by an interface chip. On switching sensors it means the signal stays below about 40–60 mV (GM, two trips; some GM engines also require the downstream sensor to read rich at the same time, since a genuinely lean mixture would show there too). On wide-band sensors (Ford from 2011, GM) it has nothing to do with the mixture: the interface chip reports one of the sensor wires shorted to ground. A really lean mixture leads to P0171/P2195 rather than this code. A stored code usually switches mixture control to open loop and suspends adaptation and converter monitoring.

Likely causes

Signal wire (or a wide-band sensor wire) shorted to ground, e.g. chafed on exhaust or gearbox
Sensor faulty or poisoned (permanently lean signal)
Large exhaust leak ahead of the sensor or misfires
Connector wet or corroded
Control module or interface chip faulty

Symptoms

  • Check engine light on
  • Higher consumption, possibly rough running (no mixture control)
  • Higher emissions, possible emissions test failure
  • Possibly with P0171/P2195

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–350
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Look for exhaust leaks upstream of the sensor
  2. Check fuel trims
  3. Inspect wiring

Parts involved

oxygen sensor bank1 sensor1oxygen sensor wiringengine control module

Related codes

P0130P0132P0134P0151P0171P2195

References: law.cornell.edu, gsi.ext.gm.com, newtonnet.co.uk, saabwisonline.com.