Corolla Nze121 Heated Oxygen Sensor Problem

[circuitravi]

My corolla nze121 illuminate engine light and it gives p0135 and p0141 (Oxygen sensor heater circuit). I check resistance in two heaters and both are open. so I need to replace it. but when I reset the fault code it only appears after some driving. why is that? why is it not appearing just start up the car? please help .... thanks!

[Rumesh88]

My corolla nze121 illuminate engine light and it gives p0135 and p0141 (Oxygen sensor heater circuit). I check resistance in two heaters and both are open. so I need to replace it. but when I reset the fault code it only appears after some driving. why is that? why is it not appearing just start up the car? please help .... thanks!

O2 sensors does not respond to changes in O2 level immediately. Also it takes sometime for the heaters and exhaust gases to warm up the sensor to bring it to working temperature after starting the car. During this period the fuel delivery is controlled by the ECU look up tables. Hence the ECU waits for sometime before it activates the CEL indication.