The oxygen sensor installs in the upstream position on select 2016-2021 BMW applications. It measures the exhaust air-fuel ratio across a broad range so the engine computer can meter fuel precisely. It has a M18x1.5 thread.

Walker Products 250-25131 Oxygen Sensor Features:

• Fits 2016-2018 BMW 330e; 2017-2021 BMW 230i, 230i xDrive; 2017-2019 BMW 330i, 330i GT xDrive, 330i xDrive, 740e xDrive
• Fits 2017-2020 BMW 430i, 430i Gran Coupe, 430i xDrive, 430i xDrive Gran Coupe, 530i, 530i xDrive; 2018-2020 BMW 530e, 530e xDrive; 2018-2021 BMW X3; 2019-2021 BMW X4 with the 2.0L I4 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, 575 mm (22.6 in.) overall length
• Female oblong connector at the harness end with 5 spade terminals
• Platinum electrode layer with a protective coating against combustion residue