PID 15V
O2 sensor B1S2 voltage
Rear oxygen sensor voltage (bank 1, after the catalyst).
What is normal
After a healthy catalyst the picture is smooth. If the rear one starts copying the front one, that is the P0420 conversation.
These figures hold for most cars, but the maker has the last word: some engines run hotter or idle higher by design.
Codes about this parameter
P0136Downstream O2 sensor circuit malfunction (bank 1)P0141O2 sensor heater circuit malfunction (bank 1, downstream)
Codes behind this reading
If the value is out of range, the unit usually says so with one of these codes.
P0136Downstream O2 sensor circuit malfunction (bank 1)P0137Downstream O2 sensor circuit low voltage (bank 1)P0138Downstream O2 sensor circuit high voltage (bank 1)
How it feels behind the wheel
The same fault shows itself in different ways. Each sign below says what to look at in the live data.
The engine stumblesThe engine runs unevenly, the car shakes at idle, the exhaust note stutters. On the move the pull sags and consumption rises.Fuel consumption has gone upYou refuel noticeably more often for the same driving. The lamp is usually off — the unit thinks it is coping.It smells of petrolA fuel smell in the cabin or around the parked car. Sometimes with the Check Engine lamp on.Smoke from the exhaustVisible smoke from the tailpipe. The colour is the clue: white, blue and black mean entirely different things.Check engine came on after refuellingYou filled up, drove a few kilometres, and the light came on. The car drives exactly as before.Check engine came on after a wash or heavy rainYou washed the car or drove through a downpour — and the light came on. It often clears itself in a day or two.
How to see it
In CarScan: the Live data tab, «Start polling». The app asks the car several times per second, draws a graph and remembers the highest and lowest value of the trip.