P0131 Code: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)
P0131 means the upstream oxygen sensor on bank 1 is reading persistently low (lean) voltage.
- Applies to
- All OBD-II vehicles (any make or model)
- Est. repair cost
- $60 – $350
- Time to fix
- 1-3 hours
What it means
Common causes are an aged/contaminated O2 sensor, an exhaust leak near the sensor, or a genuine lean condition. This is a generic OBD-II powertrain code defined in the SAE J2012 standard, so it applies to virtually any 1996-or-newer OBD-II vehicle — cars, trucks, and modern fuel-injected motorcycles — from any manufacturer (Toyota, Honda, Ford and the rest). Read it with any OBD-II scanner; the meaning is the same across brands, though the exact repair can vary by engine.
Symptoms
- Check engine light on
- Poor fuel economy
- Rough running; possible failed emissions test
How to fix it
- 1
Check for leaks and the O2 sensor
1. Inspect the exhaust ahead of the sensor for leaks. 2. Check live O2 data; replace an aged upstream sensor. 3. Address any lean cause, then clear the code.
Frequently asked questions
Does P0131 mean a bad O2 sensor?
Often, but not always — an exhaust leak or a real lean condition can cause it too. Check for leaks before replacing the sensor.
Last updated July 16, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.