How Do Parking Sensors Work?
- How it works
FixMyCar discusses different types of parking sensors and how they work.
Book a car repair nowEllie Dyer-Brown
Wednesday March 05 2025
6 min read
Parking sensors are a godsend for those of us who struggle to manoeuvre into tight spaces. They alert you, the driver, to nearby obstacles, turning the trickiest parallel parking attempt into a walk in the park. But how do they actually work? Let’s take a closer look.
How do parking sensors work on cars?
Parking sensors detect how close a vehicle is to surrounding objects and alert the driver with a beeping sound. There are two types of sensors: ultrasonic (the most popular type) and electromagnetic.
They aren’t 100% reliable, so you shouldn’t take them for granted - remember to use your mirrors and windows too.
Ultrasonic sensors
Most parking sensor systems use ultrasonic sensors that emit sound waves. When these sound waves hit an object and bounce back, a controller in the car calculates how far away the object is. It alerts the driver by creating a beeping sound that increases in pitch the closer the vehicle gets to the object.
Pros
Most affordable option
Can be fitted on any cars
Cons
Accuracy and range dependent on the number of sensors
No visual information
Best for: Compact vehicles and city cars.
Electromagnetic sensors
Some cars are fitted with electromagnetic parking sensors, which work slightly differently. They emit electromagnetic waves in an arc behind the vehicle. If anything disturbs this electromagnetic field, the car’s computer will detect the size and distance of the object and play a warning sound to alert the driver.
Pros
Wide detection field
Better at detecting moving objects
Fewer false alarms
Cons
More expensive
Performance can be impacted near magnetic materials like iron
Best for: Estate cars and SUVs.
Tips for using parking sensors
You should view your parking sensors as an extra tool to use with your mirrors and sense of spatial awareness. You could also use a blind spot mirror for added safety.
If you want to know what safety margin is built into the system, try reversing up to a wall until the parking sensor changes from a beeping sound to a flat tone. Get out and look at how close the wall is - this will give you an idea of how much further you could go.
Car manufacturers often create a significant safety margin, meaning parking can be quite alarming until you get used to it.
It’s also important to remember that parking sensors don’t know if you’ve fitted a towbar or bike rack, which adds a few inches to the car’s length. You’ll need to give yourself a bit more space when reversing and not rely on the parking sensors as much.
Common problems with parking sensors
A few different things can cause your parking sensors to stop working.
Dirt and debris
Built-up dust, dirt and debris on the sensor surface can stop it from functioning and lead to false readings.
Electrical faults
Faulty wiring is a common culprit of sensor failure. Problems with the control module and damaged connectors can also cause problems.
Moisture
Moisture can corrode the metal housing and electrical connections if it gets into the sensors.
Physical damage
Collisions and even minor impacts can damage the sensors.
My car doesn’t have parking sensors, what can I do?
The good news is that you can retrofit parking sensors to almost any vehicle nowadays.
Parking sensor kits come with sensors, adhesive to stick them to the bumper, a beeper for the warning, and all the necessary wiring. They are typically advertised as DIY, but because of the wiring involved, we recommend getting the job done by a trained auto electrician.
How much does it cost to get parking sensors fitted?
The average price of a parking sensor fitting on FixMyCar is £143.41.
| Car Make | Average Price |
|---|---|
| Audi | £133.85 |
| BMW | £132.18 |
| Citroen | £141.76 |
| Ford | £147.49 |
| Mercedes | £155.65 |
| MINI | £166.54 |
| Nissan | £147.37 |
| Peugeot | £154.60 |
| Renault | £139.88 |
| Toyota | £141.80 |
| Vauxhall | £147.64 |
| Volkswagen | £138.30 |
| Volvo | £159.13 |
How to reset parking sensors
You can’t really ‘reset’ your parking sensors - they either work or they don’t. However, there are a few ways you can troubleshoot them.
Clean the sensors
If your sensors aren’t working as expected, cleaning them is the first thing to try.
Fill a bucket with warm water and add car shampoo.
Dip a microfibre cloth into the bucket and squeeze it out.
Clean the sensors with the damp cloth in a circular motion.
Rinse with fresh water.
Get more car cleaning tips in this guide.
Check the sensors using an OBD tool
An onboard diagnostic (OBD) tool is a device that allows you to access recorded vehicle data and troubleshoot problems. When a problem occurs with the parking sensor system, a trouble code is sent to the car’s electronic control unit (ECU), which can be read with a diagnostic tool.
Connect the OBD scanner to your vehicle’s diagnostic link connector (DLC).
Switch the ignition on.
Select the vehicle's make, model and year on the OBD scanner and scroll to the parking aid module (PAM) section.
Start scanning.
The scanner will read any fault codes and identify which sensor is malfunctioning.
Replace the broken sensor.
Don’t have a diagnostic tool? Don’t worry. FixMyCar can help you find a reliable local mechanic for a diagnostic test.
Are there any other parking aids?
Reversing cameras
Most new cars sold in the EU from 2023 onwards must be fitted with a reversing camera, and many older vehicles have one, too. You can see guidelines to help you reverse on the screen showing the camera feed.
Surround view systems
‘Surround view’ systems incorporate sensors and cameras to provide a 360-degree image of the vehicle’s surroundings. The image is shown on the car’s display screen.
Cross traffic alert
Cross traffic alert is a safety technology that brakes automatically if another road user or pedestrian gets too close to the car during a manoeuvre.
Automatic parking systems
Automatic parking systems can park a car without much input from the driver. Some systems will steer the vehicle while you apply the brakes, throttle and change gears; others are entirely automated.
Frequently asked questions
Yes. Front parking sensors are activated when you get close to an object below a certain speed or move forward after reversing. Rear sensors are activated when you select the reverse gear and start beeping when you get close to whatever is behind the vehicle.
You can find out if a car has parking sensors by checking the rear bumper. Sensors look like small circles one or two centimetres in diameter. If you’re still not sure, try reversing towards a solid object and see if the system beeps in warning.
Parking sensors have more pros than cons, but it's worth knowing their downsides. The first is that it’s possible to become over-reliant on them and lose some spatial awareness of your car. The beeping can also be annoying and may make some drivers feel stressed while parking, leading to mistakes. Finally, parking sensors aren’t always reliable. They sometimes struggle to detect flatter objects lying on the ground.
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Written by Ellie
Ellie is FixMyCar's Content Writer. She has over three years of experience writing about cars and regularly collaborates with automotive experts to provide trustworthy advice for drivers that is easy understand. Her work has been featured in Yahoo! Finance, iNews, The Daily Express and The Sun. She has a BA in English literature and an MA in creative writing from Durham University. Outside of work, Ellie follows F1 and eagerly awaits Ferrari's next era of dominance in the sport. She drives a Suzuki Swift.