kev95

It all started ~1200km ago. CEL was illuminated and p0171 - system too lean and P0170. Replaced cam magnets and pre cat o2 sensor(Bosch), cleaned all plugs that had oil in them.
Drove about 400km and again CEL was illuminated with P0171 and P0170.
Cleaned MAF and checked 12$ hose(looks like replaced and it was in good condition but one airbox hose clamp was really loose, so I tightened it. After 80km CEL was illuminated
P0036 Heated Oxygen Sensor Control Circuit (Bank 1, Sensor 2)
P0136 O2 Sensor Circuit Malfunction (Bank 1,Sensor 2)
P0138 O2 Sensor Circuit High Voltage (Bank 1,Sensor 2)
P0141 - O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2) codes. When reading B1S2 voltage with ELM327 then it shows first at startup 0.6V, after 5 seconds it jumps above 1V and stays there with unregular 0.7-0.9V spikes.
Also after getting rear o2 sensor faults STFT is almost always very negative(rich) and next time if I start car is very positive(lean) and sometimes perfect(I know - really weird, atleast for me).
Is it possible that post cat O2 makes car run lean or rich?
Replace post cat O2? Maybe catalytic converter is dead? What to look for?

Rudeney

These all point to problems with the "downstream" or "post-cat" O2 sensor. I'd start there - check the wiring harness for poor connections or oil first, then replace the sensor.

kev95

Replaced downstream O2 sensor with new Bosch one. CEL came back after 50km driving in city. Went to mechanic to check emissions. Emisson test failed because Lambda was out of limits and CO was too high.


OBD

When I watch o2 voltage graph then it is 0.4V until closed loop. When car goes into closed loop then o2 voltage drops to 0.0V and stays there.

When I disconnected O2 sensor, then O2 voltage went to 0.4V and when I connected it again it went instantly to 0V again.
Is it possible given that information that new Bosch O2 is faulty and shorted inside?

Rudeney

I am not an expert on this, but my understanding is that that it should never go to 0.0v - it should be between 0.1v and 0.9v, so 0.4v is "normal".

kev95

My understanding about it is the same. It shouldnt go to 0.0V. But when o2 sensor is connected and should show voltage between 0.1 - 0.9V then its 0.0V. When I unplug O2 sensor from car, then ECU sees 0.4V(I think it should be like that, when sensor is disconnected).
But my question is that, is it possible that new sensor itself is shorted inside? I have 1 year warranty for that sensor, so I could just replace it, if that seems to be the problem.

Rudeney

It is possible that a new sensor could be defective.

kev95

So, It seems my car fixed it self
After I made that post #5, I cleared fault codes and drove about 800km(400 in only city). All Emissions readiness tests are in "Ready" status, and rear o2 sensor shows correct voltage and everything seems to work nicely now. Exhaust gases smell good now, no more rotten egg smell.

So I really dont know what caused new O2 to not work at beginning.

Big thanks to Rudeney, who has been very active in all my threads. I hope my English is not too bad and everybody can understand what I'm writing.

Rudeney

Glad to hear it's all clear now. And your English, well, I had no clue it wasn't your first language!