Learning, Multimeter,

How to Test Parking Sensors with a Multimeter (6 Steps)

Parking sensors are position sensors that help the driver recognize nearby objects when parking a car.

They are commonly installed on the bumpers of automobiles. Technically, they are classified as park assist sensors. However, despite having one, a parking sensor issue can still occur, causing a challenging condition. It may be hard to diagnose it unless you use a multimeter.

To test a parking sensor with a multimeter:

  • Remove the sensor from the car and set the multimeter to electrical resistance mode.
  • Locate the three-contact parking sensor (plus, signal, minus).
  • The resistance of a functional sensor between “plus” and “minus” exceeds 0.5 MΩ, but there should be a 2–40 kΩ resistance between each of the two and the signal contact.
  • If the value on either test changes dramatically, the parking sensor is damaged and must be replaced.

This article will guide you to use a multimeter to test parking sensors and what to look for when they are damaged.

Why a Parking Sensor Might Fail and What to Do

faulty car parking assistance system

A parking sensor often fails due to two common reasons:

  • Accumulation of dirt or debris on the camera’s lens
  • Loose or disconnected wiring

If you notice dirt or debris, clean it off. Use isopropyl alcohol or WD-40 with a soft cloth. Don’t use anything abrasive. Or, reattach and secure a loose wire if that’s the case. Then, re-check to see if the sensors start working.

If you still have an issue with one installed already, you must test it further using a multimeter.


Testing a Parking Sensor with a Multimeter

Step 1: Disconnect the Battery

Disconnect the wire from the battery’s negative terminal.

This is a safety precaution to avoid damaging the system while testing the sensor.

Step 2: Test the Wire Harness

Locate the parking sensor’s wire harness, usually near the front or rear bumper.

Set the multimeter to measure resistance and conduct a continuity test to see if the wires are damaged. If damaged, this may cause the sensor’s not to work. Otherwise, reconnect the battery’s negative terminal if the wires are in good condition.

We will now continue to test the sensor itself.

Step 3: Remove the Parking Sensor

man showing a park assist sensor (on the left)
Video | Jase777jase

You must remove the sensor from the vehicle to test it.

It’s usually inside a rectangular or circular box attached to either side of the bumper.

Step 4: Identify the Contact Points

Identify the sensor’s contact points or pins.

A 3-contact sensor has plus, signal, and minus contacts. A 4-contact sensor, as used on front bumpers, has an additional ground contact.

These are the two most common types of parking sensors, i.e., three-contact (pink wire) and four-contact (ground straight ahead in the front bumper).

a hand holding a pin of a 3-contact sensor
Video | Jase777jase

Step 5: Set the Multimeter

To test the parking sensor, set the multimeter to measure electrical resistance again.

Set it to the highest resistance range initially. Then, connect the black probe to the ground terminal (top or center; Pin 2) and the red probe to the live terminal (right side; Pin 1).

man testing the resistance at a lower range with a multimeter
Video | Jase777jase

Step 6: Check the Reading

The resistance of a functional sensor between the “plus” and “minus” contacts should be greater than 0.5 MΩ (the higher, the better).

Additionally, there should be a 2-40 kΩ resistance between the “minus” and the signal contact and between the “positive” and the signal contact. The exact value depends on the sensor. See its manual for the expected value.

There must be no break or short circuit at any of the connections. Otherwise, the sensor will not perform as designed when placed on the car again and could even put one in danger if it malfunctions while driving.


Park-Assist Sensor Advantages and Operation

sound wave in a car

With varying car dimensions and parking spots reducing, park-assist sensors are becoming increasingly common. They are a vital safety feature.

Advantages of Park Assist Sensors

Parking sensors offer several advantages:

  • They reduce blind spots around the car, making the complex process of parking in tight places easier.
  • They help lower driver stress and fatigue.
  • They help create a better understanding of the environment behind the vehicle.
  • They minimize the possibility of harming the car and surrounding areas.

How Park-Assist Sensors Operate

Depending on their location, there are two primary types of sensors: front bumper sensors and rear bumper sensors.

The rear parking sensors activate when the driver shifts into reverse gear. They send ultrasonic waves. When these waves collide with a nearby object, the sensors reflect and recapture them. The ECU determines the distance of the item from the vehicle based on the time elapsed between the transmitting and recapturing waves. [Britannica]

If the car gets too close to an object, the parking system warns the driver with an audible tone or a visual indicator. As the vehicle approaches the object, the loudness of the alarm tone increases, urging the driver to stop immediately.

Aside from these sensors, some carmakers use reverse parking sensor cameras to offer a more precise picture of the environment behind the vehicle. Vehicle reverse-parking sensors are often built to provide an update from a significant distance away from other objects. [Greatist]

Differences between Ultrasonic and Ultramagnetic Parking Sensors

They operate on either an ultrasonic or an electromagnetic principle. The table below lists a few differences between ultrasonic and ultramagnetic parking sensors.

Ultrasonic Parking SensorUltramagnetic Parking Sensor
InstallationFour or six sensors are commonly mounted on the bumper.Installed on the inside of a bumper.
Operation
They produce ultrasonic waves that bounce off items in their path. When the sensor detects a reflection, it transmits information to its central unit. It finds how far away the item is based on the time difference between the arrival of each wave back to the sensor.
Use more current and are more reliable but more expensive.
UsageCommon in most automobiles
Very uncommon; not as widespread as ultrasonic parking sensors.
DrillingNo drilling is required.
Drilling is usually necessary, but they are rugged and engineered to survive harsh weather conditions.




References

Britannica. Electromagnetic principle. https://www.britannica.com/science/electromagnetism

Greatist. Ways to help the environment. https://greatist.com/happiness/ways-help-environment

Video Reference

Jase777jase

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About Sam Orlovsky

AvatarCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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