How to check bad parking sensors

Parking sensors are a standard feature in cars nowadays. Although they rarely fail, it’s good to know how you can check them when there are some problems.

There are some easy ways for you to check parking sensors that are not functioning properly. These checks include a simple tactile examination, a multimeter, or even a smartphone. Scanners are also another good way to perform the check

I will describe each method later in this article.

How do parking sensors work?

There are two types of parking sensors, ultrasonic, which is more common, and electromagnetic. The principle of ultrasonic parking sensors operation is based on the fact that they emit ultrasonic waves and catch their reflection from an obstacle. The distance between the sensor and the interference is calculated by the main unit based on the difference in radiation time.

Electromagnetic sensors are tape that emits an electromagnetic field. The tape is installed on the inside of the front and rear bumper. These sensors are more modern and reliable, but quite expensive, so they are quite rare and only on premium cars.

Parking sensor malfunctions

  • contact corrosion, moisture entering the housing through cracks;
  • failing electronic component of the sensor;
  • contamination of the working surface of the parking sensor;
  • mechanical damage to the sensor as a result of an accident or impact;
  • damage to the wiring (especially typical for the front sensors due to dirt and chemicals);
  • manufacturing defect of the parking sensor, or its low quality (most often aftermarket, fake).

As a result of damage to one or more sensors, the Parktronic system may either not work at all, or, on the contrary, constantly beep, triggering false signals. And when the sensor wires are shortcircuited, especially, in rainy weather, a parking sensor error may display on the dashboard.

Also, sometimes car owners think that the fault occurred due to dirt on the sensor’s working surface or the fact that it was painted to match the color of the front or rear bumper.

How to check the parking sensors?

You can check the ultrasonic parking sensors in four ways: tactile, using a smartphone, using an electronic tester, and using an electronic error scanner.

Tactile check

It makes sense to start checking the parking sensor with a visual inspection. However, before doing this, you must start the engine and put the car in the first gear or reverse, but not drive. To work, you will need another person who will perform these actions in the car, while you inspect the sensors.

To check the rear parking sensors, put the gearshift in reverse. To check the front sensors, you need to engage in the first gear on the manual transmission or set the “Drive” mode on the automatic transmission.

When the sensor is operational and activated, it emits barely discernible clicks (about 5…10 clicks per second) when an object is directly approaching it (it is easiest to check with your finger).

If you put your finger on it, the sensor surface should vibrate slightly. For a better feeling of vibration, you need to move your finger a little over it.

Then, you need to check each parking sensor. At the same time, the partner in the cabin should monitor how the system reacts to touching the sensors.

This will help you determine which sensor is bad. If all the sensors do not work, there are most likely problems with the parking sensor module or the wiring.

Checking the parking sensors with a smartphone

There are parking sensors that have a very weak vibration and the sound emanating from them is practically not captured by the ear. In this case, it makes sense to use a voice recorder on a smartphone for diagnosis. 

However, you don’t need just a simple voice recorder, but an application that allows you to build a diagram of the incoming sound. The operating system and the application itself are irrelevant in this case.

Checking the parking sensors with a smartphone

For diagnostics, you need to activate the app and bring the microphone to the parking sensor. Recording the signal should take about 30 seconds.

In the end, you need to listen to the recording. First, if there are signals, they will be visible on the chart. And second, there will be audible clicks on the recording from a functioning sensor.

It’s best to do this in a very quiet place.

Checking the parking sensor with a multimeter

The most reliable method of checking the parking sensors is to use a multimeter. To do this, the tester must be set to the electrical resistance measurement mode, and the sensors need to be removed from the car.

The resistance value for different sensors will differ, however, it is important to check that there is no break or short circuit. Three-contact parking sensors usually have the following Pinout: the first contact is a “plus”, the second contact is a signal, and the third contact is a “minus”.

In a working sensor between “plus” and “minus”, the resistance should be more than 0.5 megohms (the higher – the better). 

Between the” minus ” and the signal contact, there should be a resistance of the order of 2 – 40 kOhm (depending on the sensor). There will be a similar resistance between the signal contact and the “plus”, about 2 – 40 kOhm.

In some cases, even for bad parking sensors, the value of the measured resistances will be normal, so if this is the case, then additional diagnostics must be performed.

Checking the parking sensors with a piezoelectric element

Parktronic sensors are essentially piezoelectric elements. They change their shape (vibrate) from the voltage applied to them. There is also a reverse effect.

When the piezoelectric element vibrates, it generates a voltage. This effect can be used for checking. To do this, you will need a different Parking sensor (only not standard) with a shielded wire and two LEDs.

These LEDs must be soldered to the output wire of the sensor in a counter-parallel circuit. This will allow the LEDs to glow alternately in their polarity.

Next, you need to wipe the sensor membrane and attach it to the sensor being tested on the car. If it vibrates, the LEDs will flash. This method is well suited for testing those parking sensors that do not vibrate when you touch them.

Checking the parking sensors with a scanner

You can also use software to diagnose parking sensors in your car. To do this, you need to have an electronic scanner.

The easiest way is a portable one on an ELM327 chip, and a diagnostic program installed on your smartphone. One of the most popular is ELM Config.

The program allows you to read errors from various car systems, including parking sensors. The section where you need to check for errors in the parking sensor is called PAM in English. After clicking on the error reading button, the program will provide the appropriate information.

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