The adaptive speed control sensor is the heart of the adaptive speed control system (see the related article in this issue of Mopar® Magazine). It’s also known as the adaptive cruise control (ACC) sensor or module, or by its more common name, the radar sensor. It is mounted in the front fascia below the bumper. As you can see from Figure 1, this sensor is in a very vulnerable spot; however, not all radar
sensors are this vulnerable. To withstand the impact from stones, rocks and other debris from the road, the lens is made from a very durable material. The lens material, however, cannot keep the sensor from becoming dirty from bugs, road tar, mud and other natural elements, like snow.
Whenever the front fascia is damaged and is removed, or replaced, the radar sensor has to be realigned. Failure to properly align the radar sensor will result in improper operation of the adaptive speed control system.
Radar Sensor Basics
The radar sensor, or ACC module, is mounted to the front bumper beam at the centerline of the vehicle. The number of fasteners varies from model year to model year. Basically, the radar sensor is mounted to a bracket, which is mounted to the bumper. Usually, there is one fixed ball stud and two adjustable ball studs (vertical adjustable and horizontal adjustable) that secure the module housing of the radar sensor through a pressed fit into the molded plastic ball socket clips installed in the mounting bracket
The radar sensor pivots on the fixed ball stud while the upper adjustable ball stud allows the module to be vertically aligned. On earlier modules, horizontal alignment is performed electronically using a scan tool. On newer models, such as the 2017 Chrysler Pacifica, the lower ball stud allows the module to be horizontally aligned after installation. It has a molded plastic module cover with a center clearance hole for the module lens/radar dome that snaps over the module. This cover conceals a small square mirror and the adjustment screws. The mirror is only used for calibration purposes during the vehicle assembly process.
On all models, the adjustable ball studs and the radar sensor cannot be repaired. If ineffective or damaged, the entire module unit must be replaced. The module bracket assembly must be replaced if service is needed. This is to ensure proper functionality and the press fit nature of the clips.
Replacing the Radar Sensor
Replacing the radar sensor is rather straightforward. Start by disconnecting and isolating the battery negative cable. Next, raise and support the vehicle. Remove the front lower fascia closeout cover.
Replacement procedures vary depending on the year and model (this design of adaptive speed control was introduced in 2011). For this article, we will look at the removal/installation procedures for the 2011 Chrysler 300. First things first, though. Regardless of the model and year, remove the fascia.
Refer to Figure 2. If equipped, unsnap and remove the sensor bezel (mirror cover) #3 from the face of the radar, or ACC, sensor. The sensor is located below the right side of the front bumper support bar. Disconnect the wire harness connector (#5) from the connector receptacle.
Firmly grasp the sensor housing and pull it sharply forward from the sensor mounting bracket (#2) until the one fixed and two adjustable ball studs unsnap from the three molded plastic ball socket clips in the bracket.
NOTE: The three molded plastic ball socket clips in the bracket MUST be replaced with new ball socket clips whenever the sensor is removed from the bracket; the ball socket clips are removed by rotating the clips counter-clockwise.
Before installing the new radar sensor, remember to replace the ball socket clips in the mounting bracket. To install the new radar sensor (refer to Figure 2), position the new sensor to the mounting bracket. Align the three ball studs (one fixed and two adjustable) with the three ball socket clips. Using hand pressure on the face of the sensor unit, press firmly and evenly until the ball studs snap into the ball sockets.
Reconnect the wire harness connector (#5) to the connector receptacle. If equipped, snap the sensor bezel (mirror cover) (#3) over the face of the sensor. Check the vertical alignment of the sensor, then re-install the fascia. Use a scan tool to perform the horizontal sensor alignment procedure.
Aligning the Radar Sensor
After the radar sensor has been replaced, or re-installed in the fascia, it must be re-aligned. To accurately align the radar sensor, place the vehicle on a wheel alignment or frame rack to achieve the proper sensor vertical alignment results. If a wheel alignment or frame rack is not available, then a verified level surface can be used. When using the wheel alignment rack, the fore-aft specifications must be within 0 +/- .2 degrees. Verify that the normal tire pressure and vehicle suspension height are normal. Rock the vehicle side-to-side three times, then jounce the front and rear suspensions three times.
Radar Sensor Alignment Procedure for 2011 Chrysler 300:
- Unsnap and remove the molded plastic fascia closeout bezel in the center of the grille of the front fascia to gain access to the sensor adjustment screws.
- Remove the smaller plastic mirror cover bezel from over the front of the sensor housing.
- Using standard glass cleaner and a clean soft towel, remove any dirt or road salt from the convex molded dark plastic lens
(radar dome) on the face of the sensor as well as from the suction cup of the vertical alignment tool.
- Carefully slide the vertical alignment tool over the sensor housing until the suction cup rests against the lens of the sensor.
NOTE: It may take several attempts to get the suction cup of the special tool to fasten securely to the sensor; if necessary, lightly wet the suction cup with clean water to help improve adhesion.
- Depress the plunger of the vertical alignment tool to engage the suction cup and attach the special tool securely to the lens of the sensor.
- Check the location of the bubble of the spirit level on the vertical alignment tool; it should be centered between the two center marks; if it is not centered, use the 3.5-millimeter hex nut driver to rotate the vertical adjustment ball stud as necessary to center the bubble.
- Depress the center release button of the special tool to release the suction cup from the sensor lens and remove the special tool from the sensor.
- Re-install the smaller plastic bezel (mirror cover) and the molded plastic ACC fascia closeout bezel onto the front of the sensor housing.
- Perform the radar sensor horizontal alignment using a diagnostic scan tool and the appropriate diagnostic information.
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