What i should do after 5 baud init? i tried everything. Fast init it's not supported that's why i'm using 5 baud slow init.

This is the simple circuit i'm using:



It should work because i get correct response  

This is the code:

//5 Baud Slow Init

  digitalWrite(TX, HIGH);
  delay(5000);
  digitalWrite(TX, LOW);
  delay(200);
  digitalWrite(TX, HIGH);
  delay(200);
  digitalWrite(TX, LOW);
  delay(1400);
  digitalWrite(TX, HIGH);

  Serial.println(F("##### Answer reading #####"));
 
  for(byte n=0;n<6;n++) 
  {
    Serial.print(softSerial.read(), HEX);   //It answer correctly 0x55 0x01 0x8A
    delay(500);     
  }


After that, i send 0x75 (the complement) but i get no response 
 

The problem here is that i successfully receive 5 baud confirmation 0x55 0x01 and 0x8a but after sending 0x75 i have nothing.... i'm using altsoftserial, every sketch i saw on internet use a software serial and they have no problems. I also tried a sketch from "Alexander’s car diagnostic software (OBD KW1281)" but can't get it to work :/

already tried that, not working

You probably have wrongly configured the baud rate or the stop/start bits.
Also don't wait too long to send 0x75. Of course don't send it TOO fast either, there are some communication timings to take care of.

In your example you have a 500ms delay there. For every printed byte!
3 bytes - 1500ms delay, where you don't answer ECU.
That's too much! It will close comms, that's why you never get reply to your 0x75.

It's been a long while since I wrote a KWP1281 tool. But IIRC after 0x75 the normal "ping pong" should initiate.
Watch the timing and get some elementary coding basics down.