An O2 sensor spacer changes the position of the downstream oxygen sensor in the exhaust stream. Before installing one, diagnose the underlying issue and confirm that the part fits your vehicle and complies with local emissions requirements. What does an O2 sensor spacer do? The spacer moves the sensor slightly away from direct exhaust flow. In some modified exhaust systems, this may help reduce recurring efficiency-related codes such as P0420 or P0430. It is not a replacement