user69598: I am making a line follower robot. The issue is trying to make the motors run.
The L239D module has 4 input pins (to control two motors), 4 output pins (to drive motors), and 6 power pins (5V, 5V, GND, GND, 9/12V, and 9/12V).
I have used one 5V pin to connect it to an Arduino's 5V supply and one of the 9/12V pins to two 9V batteries in series.
The motors are barely running and when the robot is on the ground it is not able to move. I even tried three 9V batteries in series to get the voltage up to 27V but it doesn't help.

user61722: 9 V 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.

69598: <p>I am making a line follower robot. The issue is trying to make the motors run.</p>
<p>The L239D module has 4 input pins (to control two motors), 4 output pins (to drive motors), and 6 power pins (5V, 5V, GND, GND, 9/12V, and 9/12V).</p>
<p>I have used one 5V pin to connect it to an Arduino's 5V supply and one of the 9/12V pins to two 9V batteries in series.</p>
<p>The motors are barely running and when the robot is on the ground it is not able to move. I even tried three 9V batteries in series to get the voltage up to 27V but it doesn't help.</p>
 61722: <p>9 V 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.</p>
<p>Putting them in series will give you a higher voltage, not more current, and the higher voltage could damage something else in the circuit.</p>
<p><em>Assuming you connected everything correctly, including ground:</em> you need bigger batteries. Even 6 AAs in series would be much better than using a 9V battery for getting your robot to move.</p>
