Parking: an eternal challenge for every driver
Admit it, we have all scraped a bumper at least once while trying to squeeze into a tight parking spot. Or missed a low bollard behind the car. Or got too close to a wall. Parking sensors and reversing cameras are inventions that have saved countless bumpers, and nerves too.
The trouble is that these systems are not cheap, especially when they need replacing. A new original parking sensor costs 30 to 100 euros each, and when you need four on the rear bumper, it adds up fast. A reversing camera can cost over 200 euros for an original part. Then there is the fitting.
Used parking sensors and cameras are an excellent chance to save. But there are specifics you need to know about, from the sensor colour to the camera's compatibility with your infotainment system.
How parking sensors work
Parking sensors use ultrasonic waves to measure the distance to obstacles. The principle is the same as with bats: the sensor emits an ultrasonic pulse, the pulse bounces off the obstacle and returns, and the system measures the travel time of the sound and works out the distance.
A typical system has 4 sensors on the rear bumper, and many cars also have 4 on the front. The sensors are usually 18 to 22 mm in diameter and fitted into holes drilled in the bumper. The control unit (ECU) processes the signals from all the sensors and gives the driver feedback through audio signals (beeps) or a visual display on the screen.
As you get closer to the obstacle, the beeping gets faster, and when you are at the critical distance (usually 20 to 30 cm), it turns into a continuous tone. Some systems also show a graphic distance display on the screen, with different colours for different distance zones.
Components of a parking sensor system
- Ultrasonic sensors - small round sensors in the bumper, usually 4 at the rear and optionally 4 at the front
- Control unit (ECU) - receives signals from the sensors and generates warnings
- Buzzer - produces audible warnings, usually placed inside the cabin
- Wiring harness - connects the sensors to the control unit
- Switch - turns the system on and off, usually automatically when reverse is engaged
The most common parking sensor faults
Parking sensors are exposed to the elements and to mechanical damage, so they fail fairly often:
Sensor damage - a knock on the bumper, even a light one, can damage a sensor. A crack in the sensor housing lets moisture in, which destroys the internal electronics.
Dirt and ice - mud, snow or ice on a sensor can block the ultrasonic signal. That is not a fault as such, but the system gives false warnings or fails to warn when it should. Cleaning usually fixes it.
Connector corrosion - connectors on the rear bumper are exposed to water and salt, especially in the winter months. Corrosion breaks the signal and the sensor stops working.
Damaged cable - the cable from the sensor to the control unit can be damaged mechanically or by corrosion. It is especially vulnerable at the transition between the bumper and the body.
Faulty ECU - the system's control unit can fail, usually because of moisture or a voltage spike. When the ECU fails, no sensors work.
Used parking sensors: what you need to know
Buying used parking sensors is a fairly safe thing, but there are a few things you must watch:
Sensor colour
Parking sensors are painted in the bumper colour. If you buy a used sensor, ideally find one in the same colour as your bumper. Otherwise, the sensor will stand out visually. Of course the sensor can be repainted, but that adds cost and work.
An alternative is to buy a sensor in any colour and paint it. Just be careful not to apply too thick a coat of paint, because that can affect the sensitivity of the ultrasonic sensor. A thin coat of paint is fine, but a thick coat can absorb ultrasound and reduce the range.
Compatibility
Parking sensors must be compatible with your vehicle's control unit. As a rule, sensors of the same make and generation are interchangeable. But if you have a specific system (e.g. with a graphic display on the screen), check that the sensor matches.
There are also differences in the operating frequency of sensors. Some run at 40 kHz, others at 48 kHz. If you swap in a sensor that runs on a different frequency, the system may not recognise it.
Testing
Testing a parking sensor is simple: connect it to a power source (12V) and hold your hand in front of it. You should feel or hear a faint clicking, which is the ultrasonic pulse. If there is no clicking, the sensor is faulty.
A more advanced test is to connect the sensor to the control unit and check whether it responds to obstacles. But for that you need access to the vehicle.
Reversing cameras
A reversing camera gives you a picture of what is behind your car. It is usually placed above the licence plate or in the boot handle, and the image appears on a screen in the cabin when you engage reverse.
Modern cameras also show guide lines on the screen that move with the steering position, showing where the car will go when it moves backwards. Some have night recording, a wide-angle lens (170 degrees), and dynamic guide lines.
Types of cameras
- OEM cameras - original cameras fitted by the maker. They are integrated with the infotainment system and show up on the factory screen. Usually the best picture quality and integration.
- Aftermarket cameras - cameras fitted later. They are cheaper but need an extra screen or an adapter for the existing screen.
- Mirror cameras - they replace the interior mirror and have a built-in screen that activates when reverse is engaged.
Used cameras: what to watch for
Reversing cameras are more delicate than parking sensors and need more attention when buying:
Picture quality - over time, the camera lens can fog up or get scratched, giving a blurry image. If possible, ask the seller to show you the picture from the camera before buying.
Compatibility with the screen - OEM cameras must be compatible with your infotainment system. A camera from a newer model may not work with a screen from an older model, even within the same brand.
Water resistance - the camera is exposed to water, especially when you wash the car or drive in the rain. Check that the rubber seals are not damaged or hardened.
Cable connector - the camera's connector must be clean and undamaged. Corrosion on the connector is a common cause of poor picture or complete failure.
Prices of used parking sensors and cameras
Here is a price overview so you know what to expect:
- Used parking sensor (each): 5 to 20 euros
- New parking sensor (each): 15 to 80 euros
- Used ECU for parking sensors: 20 to 80 euros
- Used OEM camera: 30 to 120 euros
- New OEM camera: 100 to 400 euros
- Used kit (4 sensors + ECU): 40 to 150 euros
As you can see, the saving on used parts is significant, especially with kits and cameras.
Fitting parking sensors
Replacing a single sensor is a trivial job:
- Remove the bumper or access the sensor from the inside
- Unplug the old sensor's connector
- Pull out the old sensor (it usually just presses into the hole)
- Fit the new sensor
- Plug in the connector
- Test
On some cars, the sensors are accessible without taking the bumper off. On others, the bumper has to come off, which adds 30 to 60 minutes to the job but is not technically demanding.
If you are upgrading a car that does not have factory parking sensors, the job is more involved: you have to drill holes in the bumper, run cables, and fit a control unit. A used kit from another car of the same make can be an ideal solution for such an upgrade because it comes with all the needed components.
Upgrade: parking sensors and a camera from a higher trim
An interesting option is upgrading with used parts from a higher trim of the same brand. For example, if you have a basic trim without parking sensors, you can source used sensors, an ECU and a wiring harness from a higher trim and fit them.
This takes a bit more know-how and sometimes a software activation (coding) via a diagnostic tool, but it is doable on many brands, especially VW/Audi/Skoda/Seat (the VAG group), BMW and Mercedes.
On the PoDi platform you can specify exactly what you need for the upgrade and get offers from suppliers who have experience with such projects.
360-degree cameras and advanced systems
Newer cars have advanced systems with multiple cameras (front, rear, left, right) that together create a top-down view, the so-called bird's eye view. These systems are more complex and replacing them with used parts needs more attention around compatibility.
Every camera in a 360-degree system has to be calibrated so the image is stitched properly. Replacing one camera with a used one usually calls for recalibration on specialist equipment. Even so, the saving on used cameras can be significant because new cameras for these systems are exceptionally expensive.
Tips for a longer parking sensor life
- Clean the sensors regularly of mud and salt, especially in winter
- Avoid washing the sensors with high-pressure water from close up
- When you wash the bumper, be careful around the sensors so you do not dislodge the seals
- If you notice that one sensor is not working, replace it as soon as possible because driving with a partial system can create a false sense of safety
- In winter, clean ice off the sensors before driving because ice blocks ultrasound
Parking sensors and cameras are parts that significantly raise the safety and comfort of driving. With used parts, that technology becomes accessible to anyone regardless of budget. Check the part before buying, watch for compatibility, and enjoy worry-free parking.