P0131: O2 Sensor Circuit Low Voltage
P0131 means the upstream oxygen sensor (Bank 1 Sensor 1) voltage is too low or stuck low — which confuses fuel-mixture control.
Symptoms
Higher fuel use, slight weakness, sometimes rough idle, with a check engine light.
Causes
An aged/failed oxygen sensor, an air or exhaust leak near the sensor, damaged wiring/connector, or a genuinely lean mixture.
The fix
Check wiring, connector and exhaust leaks first, and watch the live sensor reading via OBD2 (it should switch). Replace the sensor if it is slow/stuck.
FAQ
Can I drive with P0131?
Short-term yes, but it raises fuel use and emissions and can confuse other codes — address it soon.
P0131 or P0132?
P0131 is low voltage, P0132 is high — both for the same upstream sensor on Bank 1.