No echo received warning causing my HR-SC04 ultrasonic module (distance sensor) to cause an output error

No echo received. Why? I want to have a robot that will move, when it gets to a wall move backwards and turn the way with lesser objects, I am using Thonny on a pi3 and I am seven years old. I put:

import time
from gpiozero import CamJamKitRobot, DistanceSensor

pintrigger = 27
pinecho = 22
pinTrigger = 17
pinEcho = 18

robot = CamJamKitRobot()
sensor = DistanceSensor(echo=pinecho, trigger=pintrigger)
sensor2 = DistanceSensor(echo=pinEcho, trigger=pinTrigger)

hownear = 50.0
reversetime = 0.5
turntime = 0.75

leftmotorspeed = 0.5
rightmotorspeed = 0.5
motorforward = (leftmotorspeed, rightmotorspeed)
motorbackward = (-leftmotorspeed, -rightmotorspeed)
motorleft = (leftmotorspeed, 0)
motorright = (0, rightmotorspeed)

def isnearobstacle(localhownear):
    distance = sensor.distance
    
    if distance < localhownear:
        return True
    else:
        return False
def avoidobstacle():
    print("Backwards")
    robot.value = motorright
    time.sleep(reversetime)
    robot.stop()
    while sensor2.distance < 50:
        print("Right")
        robot.value = motorright
        time.sleep(turntime)
        robot.stop()
        print(sensor2.distance * 100)
        while sensor2.distance < 50:
        print("Right")
        robot.value = motorright
        time.sleep(turntime)
        robot.stop()
        print(sensor2.distance * 100)
    while sensor2.distance < 50:
        print("Right")
        robot.value = motorright
        time.sleep(turntime)
        robot.stop()
        print(sensor2.distance * 100)
    
    while sensor.distance < 50:
        print("Left")
        robot.value = motorleft
        time.sleep(turntime)
        robot.stop()
        print(sensor.distance * 100)

try:
    while True:
        robot.value = motorforward
        time.sleep(0.1)
        if isnearobstacle(hownear):
            robot.stop()
            avoidobstacle()

except keyboardInterupt:
    robot.stop()

Why is there no echo receiving?