FIXONICBefore you begin
One year after replacing the rear oxygen sensor of my 2010 Mazda 5, the yellow engine warning symbol came on again. I read out the error code, with my 'OBD 2' device, and it was again reporting fault code P0138 ("bank 1 sensor 2") problem https://cartreatments.com/p0138/ As the device was fairly new, I susptected it was something else. Clearing the fault code while the engine was warm, seemed to work, so I suspected the built-in heat element was not working. However the fuse #37 was OK (see https://www.autogenius.info/mazda-5-2007...) I then removed the sensor and cleaned it using ultrasound (and gazonline), but that did not solve the problem. In disbelief I went on and checkes all (!) the relays, but they alle seemed OK Finally I decided to order a new sensor from a webshop (somehow all webshops I found seem to share the same Berlin address...). This is the part I ordered: https://www.motordoctor.dk/products/8126... Before mounting the new sensor, I did a non-scientific check of the pins (see the steps below) and the results are listed in this table: PinsNew sensorOld defect sensor1-25.06 Ohm6.2 Ohm1-348 pF6.5 Ohm1-449 pF52 kOhm2-346 pF0.9 Ohm2-449 pF53 kOhm3-446 pF53 kOhm As you can see from the table above, there clearly is a difference in the behaviour of the new and the old device. I installed the new device and followed the instructions: clear the error codesdisconnect the car battery for som minutestake the car for a 10 minute drive After this, the problem was gone.
