What does code P0133 mean on a Subaru and is it safe to drive?
P0133: O2 Sensor Slow Response (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 responding too slowly to changes in exhaust composition. A healthy O2 sensor switches between rich and lean several times per second; a sluggish sensor causes poor fuel control.
Common causes for your Subaru
- Aging or contaminated upstream oxygen sensor
- Oil or coolant contamination fouling the sensor
- Carbon buildup on the sensor tip
- Weak heater circuit in the sensor
Symptoms
- Check Engine Light
- Slightly decreased fuel economy
- Possible rough idle
- Failed emissions test
Typical fixes
- Replace upstream oxygen sensor
- Check for oil/coolant burning that could foul new sensor
Repair cost range
For a Subaru, repairs for P0133 often fall between $100 and $300, depending on the cause and whether you use OEM or aftermarket parts. Labor rates vary by location.
Known issues on Subaru
Subaru EJ25 P0133 upstream sensor—the Bank 1 sensor wiring routes along the hot front exhaust pipe and heat damage to the harness insulation is a common cause of false slow-response codes. Inspect the wiring before replacing the sensor.
Most commonly affected models