My Ultrasonic sensor is only showing 4cm range? I am using an ultrasonic sensor SR04 with Arduino Uno and a sample program which I got from the library. However, my output reading is only 4 cm even when there is no object in front of it. I even used another sample program which had the same output. Is the problem in sensor or library?

#define TRIGGER_PIN  12
#define ECHO_PIN     11
#define MAX_DISTANCE 200

NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE);

void setup() {
  Serial.begin(115200);
}

void loop() {
  delay(50);
  Serial.print("Ping: ");
  Serial.print(sonar.ping_cm());
  Serial.println("cm");
}
Looks to me like your powering the SR04 with 3.3v instead of 5v.