2008 Aveo hatch ECU/ECM question/ bad ground??

My aveo is throwing a code P0300 on cyl 1 and 4. And I only found out when I scanned it. I tried all the fix: change coil, 02 sensor, changed plugs, plug cables, clean MAF, clean fuel injectors but the code is still there.
What I observed :
1.My CEL dont light up to give me a warning.
2. I noticed that the CEL also dont light up when I turn on the car, you know it supposed to light up together with the oil, abs, battery etc.
3. ECU is throwing diff code aside from P0300. sometimes, the TPS, O2 sensor, and when I repeat the scanning.. Its gone! And goes back to P0300.

I googled and I found out that these signs are possible of an ECU bad ground or a dying ECU.
Can anyone here please tell me where can I find the ECU ground? Or anybody here have this kind of a problem? This is frustrating. Thanks in advance

anyone who can help?