P0133 Subaru Forester
O2 Sensor Slow Response (Bank 1, Sensor 1) · Powertrain Code · Medium · Repair: Moderate
What is P0133?
The upstream O2 sensor on bank 1 is responding slower than expected, reducing fuel control accuracy.
When the Subaru Forester triggers code P0133 (o2 sensor slow response (bank 1, sensor 1)), it typically points to an issue in the powertrain system. Below you'll find the most common causes, symptoms, and repair options specific to the Subaru Forester.
This repair is rated moderate, meaning some experience and specialty tools required.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Subaru Forester.
Common Causes on Subaru Forester
- Slow-responding front O2 sensor nearing end of service life
- Exhaust leak at the header or up-pipe gasket
- Fuel delivery inconsistency from partially clogged injector
- Carbon deposits on O2 sensor element
Symptoms
- Check Engine Light on
- Slight decrease in fuel economy
- Possible intermittent rough idle
- Failed emissions inspection
Notes for Subaru Forester
Subaru boxer exhaust systems have multiple gasket points; a small header leak can cause persistent P0133 codes.