Why is the check engine light on?

You will need to have this diagnosed by a mechanic, or take it to an auto parts store that can read the codes for you. You likely have a problem with your emission control systems and left alone, this can cause damage. You may be able to turn it off by disconnecting the battery and reconnecting it, but without fixing the problem, it will come back on as soon as the car is started again.

Disconnect the two lines from battery (line + and line -) and connect them together for some seconds then re connect them to battery. the engine light gets off

Thank You for your answer. I no longer own the 2001 toyota Corolla. I sold it to Toyota for another car which i ended up giving back because of financial issues. However, I will Keep in mind about what you said. Thanks again for your answer.

Thank You for your answer. I no longer own the 2001 toyota Corolla. I sold it to Toyota for another car which i ended up giving back because of financial issues. However, I will Keep in mind about what you said. Thanks again for your answer.

Check engine light on. Scanned for codes, O2 sensor bank not within threshold. Changed O2 Sensor. Most catalytic Converters today are not quite right, therefore we need a alternative. For Approximately $45.00 O2 Sensor CEL Eliminator which is a mini catalytic convertor to reduce computer reading, attach to Cat screw in actual O2 sensor into it, clear codes and done. It Works.