HC-SRO4 Ultrasonic module range


I am using an ultrasonic distance sensor to measure range (duh). When I first got the sensor, it seemed to measure up to about 300cm, but recently it is maxing out at about 200 to 150cm. Do these sensors degrade over time? Do I have a bad sensor? I have read other people saying that it is common for these to only reach about 150cm - can anyone who has worked with these give me their experience?

Edit: This range limitation occurs whether I ask for a measurement every second or every 20 milliseconds. It happens indoors and outdoors and different types of indoor rooms

It hasn't been my experience that they degrade with time, but all such sensors are sensitive to environment and pulse repetition frequency.