The scenario is a little different. Two of the four parking sensors are working. This will be the rear of the car. The inboard 2 work fine, the outboard 2 do not work at all. I had the bumper off.
​​​​​​All the wiring is good and I'm getting a strong clicking from the outboard sensors when in reverse but no warning beep... Thanks

 

Replace the non working sensors.
In my experience it's allways the sensor.

 

They're brand new. Thanks

 

I did replace sounder. It is behind rear glass under parcel shelf on passanger side.
You will have to pull out rear seat, back of rear seat and parcel shelf to get to it.
replacement:
I can't find in my records where I got it, It used on many different models Ford and Mazda among others:
https://www.walmart.com/ip/Car-Park-...866A/803673576
https://www.aliexpress.com/i/3256806...apt=4itemAdapt

 

"They're brand new. Thanks"
What happens when you swap the working ones with the clicking but non working ones?

 

Yikes! I would have to pull the bumper off again!

 

OK Where did you buy the new sensors?

 

I bought them a while ago so I don't remember but they are making the clicking noises as if they're working though

 

But they are not working are they?
This is what I have done
Remove rear bumper and carefully pull out all sensors
with wiring intact
Place wiring on top of thick metal bumper with sensors
pointing in the right direction.
test with your hand in front of each sensor to see which ones are not working
Remove any non working sensor and replace with a good one until they all work
NB ignition in pos 2 and g'box in reverse

 

I've had the bumper off three times. I'm done LOL. I'll live with the two center ones. This car had a backup camera Incorporated into the system anyways but thanks!

 

"This car had a backup camera Incorporated into the system anyways but thanks!"

Could well be the root cause of the problem !