I just purchased my first jeep. 1993 Cherokee 4x4.

The previous owner removed the 02 sensor when he installed a new header, it appears there is a plug where the sensor used to be.

I need to get the jeep to pass CA smog. If I screw a new 02 sensor in I should be OK with the aftermarket header or would I need to go back to stock?

also, is there just 1 sensor needed or 2?

thank you