P0138 alarm came up in my 1.3 Petrol Toyota Auris (59 plate). The diagnostics showed up the above code which points towards changing the oxygen sensor. The sensor was changed 3 times with various after market brands and after about 30 miles of driving the engine light would come back up. The sensor was then replaced with a OEM part and the light came on again after 30 miles.
Every time the diagnostics is done it always shows the same code. If the sensor is changed what other part in the car could be causing this code?