Hello to all members here. I'm new to this forum.

I'm from Macedonia.

I have MK4 1.6 16V AZD 2001 with 169xxx km, petrol.

I have problem with the lambda sensor pre-cat from august this year. I was getting P0130, P0133 and P0135 error codes. Also the engine wasn't running smooth, so I disabled the connector and was running the car without sensor at all. It was running nice and good.

3 days ago, I finnaly bought other sensor, which is second-hand (brand new are too expensive). I have replaced the sensor, connnected it to power and engine was running good. After I cleared the error codes using obd-2 connector and torque app on my phone. Take the car for a drive, all good. Check engine light didn't come on again.
Next morning I started the engine, still no check engine light. After 10sec, there it is, again showing error. It is showing P0130 and P0135 error codes. Got to clear codes again and drove it 20-25km, the check engine light didn't come on. I found out that CE light comes on only when car engine is cold. If I let my car off for 30-35 minutes, and it is still warm, the CE ligth doesn't signal errors. ONLY WHEN ENGINE IS COLD.

Is there a way to check if the sensor heater is working? Because P0135 is code for sensor heater malfunction, as I know.

Also it reads too rich A/F ratio, but the engine is running perfectly.

Sensor lambda VOLTAGE is mostly arround 0.45V (about 80% of time), but it goes from 0.1V to 1V though.

Maybe this sensor is also faulted?

Please help me. Thanks.