What does code P0131 mean on a Subaru and is it safe to drive?
P0131: O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1). Here's what it means on your Subaru, what usually causes it, what repairs typically cost, and how safe it is to keep driving.
What this code means
The upstream oxygen sensor on Bank 1 is reporting a voltage signal below the expected range. This can indicate a faulty sensor, a lean condition, or an exhaust leak near the sensor.
Common causes for your Subaru
- Failed upstream oxygen sensor
- Exhaust leak before the sensor
- Lean fuel condition (vacuum leak, weak fuel pressure)
- Damaged sensor wiring or ground
Symptoms
- Check Engine Light
- Poor fuel economy
- Rough idle in some cases
- Failed emissions test
Typical fixes
- Replace upstream oxygen sensor (Bank 1, Sensor 1)
- Locate and fix exhaust leaks
- Smoke test for vacuum leaks
- Check fuel pressure
Repair cost range
For a Subaru, repairs for P0131 often fall between $100 and $350, depending on the cause and whether you use OEM or aftermarket parts. Labor rates vary by location.
Known issues on Subaru
Subaru P0131 on EJ25 engines often indicates a deteriorated upstream O2 sensor or a small exhaust manifold gasket leak that introduces oxygen and causes a false lean reading. Inspect the front exhaust manifold gasket before replacing the sensor—EJ25 exhaust manifold gaskets are a known wear item.
Most commonly affected models