OBD codes troubleshooting 98 Lexus LS 400

[sha4000]

You are probably going to have to drop the tranny some to get enough clearance to either drill the bolt out or cut a notch in it so you can use a screw driver. I would not want to do this laying on my back so a lift is preferable.

[Exhaustgases]

It really sounds like you need a good place to do all this work your self. I would first try to clean everything.  Craigs got some good advice.

[M.Yasir]

Due to this sensor i am having check engine light and poor fuel economy, will keep you updated once i progress something, i think i should buy the whole timing belt kit with water pump and leave my car to a good garage and get everything done at once... because to repair only this small sensor it will be so labor intensive