P0137 on a Subaru: Causes, Fixes & Repair Cost

🟢 Low severity · drivable

Safe to drive — this downstream sensor only monitors the catalytic converter, so a Subaru with P0137 can be driven while you arrange the repair.

What P0137 means on a Subaru

On a Subaru, P0137 means the engine computer sees low voltage from the bank 1 downstream oxygen sensor behind the catalytic converter. Subaru's flat Boxer engine places bank 1 on the right-hand side, and this sensor only checks converter efficiency, so low voltage usually means a bad sensor, damaged wiring, or an exhaust leak rather than a fuel problem.

Is P0137 common on Subarus?

P0137 is most common on higher-mileage Subarus as the post-cat sensor ages. The exhaust layout on the Boxer engine keeps sensors close to heat and road debris, so corroded connectors and small exhaust leaks near the sensor are common triggers.

Commonly reported on: Outback, Forester, Impreza, Crosstrek.

Symptoms

Check engine light on
Usually no change in how it drives
Possible exhaust tick from a small leak
Slightly worse fuel economy if a leak is present

Common causes

most common: Faulty bank 1 downstream oxygen sensor
common: Exhaust leak before the downstream sensor
common: Corroded or damaged sensor wiring and connector
less common: Sensor damaged by road debris or water

How to fix it

Fix	DIY?	Typical cost
Replace the bank 1 downstream oxygen sensor	Yes	$70–250
Repair an exhaust leak near the sensor	Mechanic	$80–300
Repair the O2 sensor wiring or connector	Mechanic	$60–200