Saturday, 30 April 2005 17:00

Troubleshooting parking assist systems

Written by I-CAR Advantage Online
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Rear and side view mirrors at one time were the only assistance that a vehicle offered a driver trying to back into a parking space. Today, several vehicle models are equipped with a type of parking assist system that not only helps when parking, but when backing up for any reason. Some parking assist systems also help drivers when moving forward. Parking assist systems are often standard on station wagons and SUVs and are usually optional on sedans. 

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Figure 1. Three or four of these circular patterns in the bumper is one indication that there is a parking assist system on board the vehicle.
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Figure 2. There may also be a sensor array in the front bumper.
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Figure 3. Each parking assist sensor is held to the bumper in a retainer.

There are basically two types of systems: one is an array of sensors on the bumper that trigger an audible "beep" when you get too close to an object and the other is an actual video camera that sends pictures to the navigation screen in the center console.

There is a third type, but it's not yet available outside of Japan. Toyota Japan offers an option on the Prius gasoline/electric hybrid called Intelligent Parking Assist that directs the car to park itself. The driver identifies the exact spot using a navigation screen, touches a "set" button, and the car backs into the spot without any human assistance.

Since the location of the more common bumper sensor arrays puts them in harm's way in many collision scenarios, it is helpful to know how to troubleshoot and replace these sensors.

Bumper sensors

The sensors in bumper sensor systems are visible by the circular sensor face in the bumper cover like on the rear of the 2005 Cadillac XLR shown in Figure 1. One of several models that have a similar sensor array in the front bumper is the 2005 Lexus ES sedan shown in Figure 2. There may be up to four sensors in each bumper, which are connected via a wiring harness to a dedicated control module that communicates to the main body computer. The sensors are either all ultrasonic, or a combination of ultrasonic and radar. The system does not have to be active at all times. There is typically a switch in the instrument panel to turn this system on and off, with a text message or LED lamp indicating the system status.

In the case of the rear parking assist system, which is the most common, the system will only sense when the reverse gear is selected. The beeping noise, indicating the bumper is getting close to an object, usually comes from a dedicated rear speaker. The sound may intensify as the vehicle gets nearer to an object, and turn to a constant tone when the object is extremely close, about 12 inches.

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Figure 4. When this vehicle is put in reverse, a view of what is lurking in back of the vehicle shows on the navigation screen.
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Figure 5. The eye of the on-board camera system is in a protected position on the liftgate.

What can go wrong with these systems?

A misaligned or loose fitting bumper or bump-er cover can affect system operation. The sensor mountings are separate parts that are inserted in holes in the bumper (see Figure 3). This mounting can also loosen or get misaligned. Visual inspection may reveal a loose or out-of-position sensor. Ford Motor Company has a procedure for checking the alignment of the sensor array on the Ford Expedition and Lincoln Navigator. There is a test for proper sensor height and another test for ensuring the sensors detect an object in five specific distances from the bumper.

The sensors can get dirty or iced over, which can interrupt the signal communication. Ford recommends washing the bumper and sensors with high-pressure water to determine if this is the problem. There may also be a problem with the finish on the faces of the sensors. Some sensors are not painted, but others require a finish on whatever is visible on the bumper cover.

Notice in Figure 1 that the sensors match the color of the bumper cover. For the finished bumper sensors on the 2005 Cadillac XLR, General Motors cautions to not exceed 6 mils of coating thickness on the face of the sensors. Along with that caution, there is a recommendation to not refinish previously finished sensors, since excess build-up will cause the sensor to be inoperative. There are also no recommendations for methods of removing excessive finish on the face of the sensors.

If visual inspection doesn't show a problem, a diagnostic check may. Electronic faults will usually trigger a fault code, which can be identified, and diagnosed using a scan tool and following the troubleshooting flowchart procedures in the service information. The diagnosis may lead to a fault, such as a cut or pinched wire, which can be repaired. The diagnosis may also indicate a control module or sensor malfunction, which usually requires replacement of one or the other, or both. If the testing shows a problem with only one sensor, one sensor can usually be replaced. It's typically not necessary to replace all of the sensors.

Rear Camera

Parking assist systems with an on-board camera not only sense behind the vehicle, but show on the navigation screen what is hidden in the lower back blind spot (see Figure 4). The camera eye looks down from a protected position; such as under the liftgate handle like on the 2005 Infiniti QX56 (see Figure 5). A rear camera system is only practical on vans, SUVs, or trucks where there is a large blind spot behind the vehicle. These types of systems go beyond parking assist. They could also be classified as collision avoidance or a pedestrian safety device.

Again, like all electronic systems, the on-board camera systems can be diagnosed using flowcharts.


Parking assist systems are becoming a common option or even standard equipment on more vehicles every model year. The sensors for the bumper sensor type of system are in a vulnerable location and will require inspection and testing after collisions affecting that part of the vehicle. Try a visual inspection first. If a visual inspection shows sensor damage, replacement is the only option. If there is no visible damage and the system does not work, the sensors may be obstructed, or the sensors or bumper may be out of position.

This Advantage Online article first appeared in the I-CAR e-newsletter, which is published and distributed free of charge. I-CAR, the Inter-Industry Conference on Auto Collision Repair, is a not-for-profit international training organization that researches and develops quality technical education programs related to collision repair. To learn more about I-CAR, and to subscribe to the free e-newsletter, visit or contact I-CAR Marketing Communications Specialist Brandon Eckenrode at


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