Hi guys , today i was checking the car live data with my OBD scanner and i found two weird things in the o2 sensors readings , first of all this is the 1st time i scan my car because i never wanted to as i never got check engine light at least till now so i never scanned it before however today i was just checking i found the upstream o2 sensor readings is in mA !!! i tried to look for a way to change it to volt but in vain and the problem isn't with the scanner because i have another car and the reading is in volt as normal, also i found the downstream o2 sensor reading is in volt but its fixed 0.0 !!!! , i tried to look for the fuel trim i found the fuel trim is in perfect condition -2% which indicating there is no problem !!! but how is that possible to have a good fuel trim short and long but 0v at the downstream o2 ??!!!! and if i have a faulty downstream o2 sensor why don't i have check engine light or any codes ??!!!! i am so confused right now and i wish any body have some experience would help , BTW my car is 2010 Mazda 3 Sedan

Best regards

Amr