Iam making a line follower robot , the issue is coming when making motors run.The L239D module has 4 inputs pins ( to control two motors) , 4 output pins (to drive motors) , and 6 power pins (5v,5v,GND,GND,9/12V,9/12V) . I have used one 5v pin to connect it to ardunio 5V supply and one of the 9/12v pin to series of two 9v battery. The motors are running low and when it is on ground the line follower not able to move. I even tried 3 9V batteries in series to make up the voltage 9+9+9=27V but not helping. Any help Thanks in advance.
9V batteries, assuming you mean the little PP3-size ones, can't supply the current needed for driving robot motors; they are intended for low-current applications.
Putting them in series will give you a higher voltage, not more current, and the higher voltage could damage something else in the circuit.
Assuming you connected everything correctly, including ground: you need bigger batteries. Even 6 AAs in series would be much better than using a 9V battery for getting your robot to move.
On your next try use a different H-Bridge, one with MOSFET outputs, you can have a voltage drop across the L239D of 2.4V. Measure the voltage at the motor and at your batteries you will see what I am getting at. You might want to try connecting the motors directly to the battery first to see if it will do what you want.