The oxygen sensor installs in the upstream position on 2019-2020 Subaru Ascent, 2020 Subaru Legacy and Outback with the 2.4L H4 engine. It measures the exhaust air-fuel ratio across a broad range so the engine computer can meter fuel precisely. A built-in heater brings the element to operating temperature quickly after a cold start.

Walker Products 250-25152 Oxygen Sensor Features:

• Fits 2019-2020 Subaru Ascent; 2020 Subaru Legacy, Outback with the 2.4L H4 engine
• Sensor location by application: B1S1 (bank and sensor number)
• 5-wire wide-band oxygen sensor
• Built-in heater for fast warm-up
• M18x1.5 threaded mounting with a 22 mm hex
• Female oblong connector at the harness end
• Platinum electrode layer with a protective coating against combustion residue