Arduino + IR GP2D12 sensor

i am using the GP2D12 with arduino for obstacle avoiding robot. It was working fine. After some time it stopped working. I tested with the below code

/* 
 read_gp2d12_range
 Function that reads a value from GP2D12 infrared distance sensor and returns a value in centimeters.

 This sensor should be used with a refresh rate of 36ms or greater.

 Javier Valencia 2008

 float read_gp2d12_range(byte pin)

 It can return -1 if something gone wrong.

 */

float read_gp2d12_range(byte pin) {
    int tmp;

    tmp = analogRead(pin);
    if (tmp < 3)
        return -1; // invalid value

    return (6787.0 /((float)tmp - 3.0)) - 4.0;
}

I am getting only 5 to 10cm value. i am not getting more than that. Is my sensor damaged.

Is there any test method for the GP2D12 sensor.

Please help me

Thanks,
Robotsmani