87 Camry check engine light On question about what makes light come on?

There is no single thing that always makes the light come on. You need to jumper terminals TE1 and E1 of the check connector with a paper clip or piece of wire while the key is on. This will make the light flash out the code. Then look it up online.

Hello there, I did the paperclip test it was EXTREMELY HARD because you have to get the correct size paperclip then you have to clean/wipe off the dialectical grease so you get a good connection. Eventually I got it and it rendered code 21 Main o2 sensor as follows below details. Main oxygen Sensor Signal Main oxygen sensor circuit Main oxygen sensor ECU 　 During air–fuel ratio feedback correction, voltage output from the main oxygen sensor does exceed a set valve on the lean side and the rich side continuously for a certain period. My question now is can someone please advise me what website or section in the manual that will give me instructions on how to change the Main O2 sensor. Thanks for your help as I don't have a clue. Dave 　

That's why I use a piece of wire. It can be tricky but is a lot cheaper than a scan tool. The o2 sensor is the sensor that screws into the exhaust system. To remove it disconnect the plug and us a o2 sensor socket to remove it. It might need a lot of penetrating oil to get it loose. Then install a OEM style replacement sensor with some 02 sensor friendly anti-seize.

Hello there, Thanks for the help I feel so silly I found the problem it was just the wire to the O2 Sensor it corroded and broke off. I just spliced it back together and good to go now thanks. Dave