Hi Waqar, I will tell you what code 21 is, and how it can be done on pre vvti cars made before 2001. You car is EOBD compliant, so can use EOBD/OBD2 fault code readers. The 7A-FE, 4A-FE & 3S-FE engine are not EOBD compliant so cannot use the readers. What can be done is the 'paperclip' test. I use a copper wire to link terminal 4 and terminal 13 on the OBD socket. Then turn the key ignition. What happens is the EML, ABS and SRS will flash. In the case of the EML with the O2 sensor fault, it will flash twice, short pause then flash once. There will be a much longer pause then repeat the flash sequence. This is fault code 21. I have added the following pictures:- I recorded the flashes, but need to upload the video later so you can see what is happening. When we next meet, I will show you how the test is done. You can do the same test but only the ABS and SRS will flash. The best thing is that it practically free and saves on buying a reader that would not work on pre 2001/non vvti cars anyway. Konrad