Due to reduced performance, rough idle and random engine knocks I thought of doing an Engine tuning last weekend. My check engine issue was there all this time and I didn't try to fix it.
Since the person who does the engine tuning good with identifying issues with the scanner, I asked him to have look. As @PerfMad explain to me, we found OBD1 green color 3 pin connector hidden near ECU in a cover on passenger side. (Mystery solved)
I had 3 error codes related to MAP sensor & Both Knock Sensors. (Not sure the engine has 2 knock sensors) MAP sensor error went away after the cleaning and we checked it while driving and results looks normal (No sensor replacement required). It seems like both knock sensor wires were unplugged since no data can be read from the scanner. Found one located in the back of the engine just above the oil filter I have to take the car to a different mechanic to find and connect the wires first.
I will update the thread once this is done.