my accord 2003 check engine light on and d light blinking

What is your question?

Actually recently I travelled 2000 km in my car continuously. I poured 1/4 lt oil after 1000km. but after 2000 suddenly check engine light start on and d light too. And suddenly my car started to slow down and hadn't pick it up the acceleration. And when I check the engine oil level, it was right below the second dot. then immediately I poured half liter oil into the engine. After putting oil into car started well and running okay. After 30km check engine sign go off. But after 30 more km, my car broke down while driving and the same thing happened first engine light then d light too started up. when I checked my car's engine oil it was almost black color. Then I went to a closer mechanic and changed engine oil. But still the Engine light remains on, but car run same as before. The mechanic asked me to check with the transmission master. But I don't want to put more money on that if this is an expensive repair, because the car is very old. Please suggest if this is normal or not?