I was called to a shop for a complaint of a Blind Spot Monitoring Issue on a 2015 Jeep Grand Cherokee (Figure 1). The Jeep was recently repaired after a rear end collision and was delivered to the customer who drove the vehicle for about a week. There were no telltale signs that anything was wrong with the vehicle, but while driving on the highway, the Blind Spot indicators would come on at random while no vehicles were near the rear quarter panels and if there were vehicles present, the system would not alert you.
My first thoughts were a possibly of some type of electrical failure so I decided that I would perform a quick operational check on the system. When I arrived at the shop, I got in the Jeep and started up the engine. I did not see ANY warning signs on the dash directing me to an onboard problem, so this was a good thing (Figure 2). My next move was to shut the vehicle off and wait a few seconds and again start the vehicle, but quickly looking at both Blind Spot indicators in the side view mirrors to make sure they were following system strategy. This vehicle used a triangular orange indicator in the side view mirrors to alert the driver (Figure 3). These lights should come on momentarily and then go out. If they don’t come on, then the icon circuit is open or the Blind Spot Module on the affected side is inoperative. If the icon stays on constant then the icon circuit is shorted to ground or there is a failure of the Blind Spot Module operation on the affected side. In this case, the lights both came on momentarily and then they both went out. The vehicle passed this quick integrity check, so now it was time to do some intrusive testing.
I next hooked up my scan tool and did a full vehicle scan (Figure 4). There were no codes in the entire network of computers except for a Code B259B01 stored in the Radio Frequency Hub Control Module for a right front door handle sensing circuit that was no longer present. This code can be easily set by a body tech who might have removed the right front door handle of the vehicle and then turned the ignition key on, so this code I basically ignored. Both the right and left Blind Spot modules were free of trouble codes and they seemed to be functioning properly in the key on mode in the service bay. When driving on the road it becomes a different set of rules because the radar control unit will not look for objects near its location until the vehicle is moving at a certain speed. It is hard to test this system without driving the vehicle and testing its response on the roadway.
This particular vehicle did not have radar units mounted to the car body itself with a bracket so if the car was damaged, the possibility of a bent mounting bracket or a rear quarter panel not structurally correct was out of the equation. This I was told by the body assembler who worked on the Jeep. He also told me that the bumper was new and that the radar control modules were both secured into the bumper assembly.
I’m guessing that many manufacturers have opted to put these radar control modules into the bumpers for a cost issue because if the body of the vehicle is compromised within a few degrees then it would render an entire body panel as inadequate and not allow the tolerance for that “close enough” factor. The important factor to know is if the radar assembly is mounted on the body of the vehicle, a strategy must be in place to put the vehicle on level ground and actually use a bubble gauge to make sure the module housing is vertically and horizontally correct. It would not be a bad idea to check the right and left sides of the rear body to compare your results. The last thing you need would be to remove a whole bumper assembly again if there were issues with the Blind Spot mounting system.
I decided to take the car for a ride to see if I could experience what the customer was complaining about because everything at the shop was checking okay. The customer has a right to make sure their car is put back the way it was before the accident and that the vehicle functions the correct way. I started driving the vehicle on a local highway near the shop and I noticed that the Blind Spot indicators in the mirrors would go off randomly with no vehicle on either side of me. It was as if the system was not calibrated properly, but I know on this vehicle unlike a few other manufacturers that these modules will self-calibrate as you drive. Some manufacturers will offer a static or dynamic procedure for calibration while others may only offer a static procedure and if these calibrations are not performed, you will have a trouble code in the radar control modules or a message on the dashboard to alert you and the system will not operate until the calibrations are successfully performed. I now needed to head back to the shop to make sure the radar control modules were not loose in the bumper or had a harness that was rubbing and shorting out the indicator circuits without setting trouble codes.
I got back to the shop and instructed the body shop installer to pull the bumper so we could look over the wiring and components (Figure 5). I could not see anything damaged and both control modules seemed properly secured into the bumper housing. I removed the left rear control module to check it for structural damage and could not see any cracks or loose connections (Figure 6). When I was placing it back where it was mounted, I noticed that the module could fit facing in either direction. Then it dawned on me!! These modules were both facing the wrong direction and were picking up the vehicle’s quarter panel as the obstruction.
The flat metal part of the housing had to be facing towards the vehicle body and the plastic side had to be facing the bumper. This was a VERY easy mistake for anybody to make and it’s more the manufacturers fault to allow a dual positioning possibility. I was very surprised that the manufacturer would not simply have a marking that said “This Side Facing Out.” I positioned the left radar module in the proper direction (Figure 7) and secured the other module in the proper direction as well. I then instructed the body assembler to put the bumper back on and I would go for another ride to make sure all was well before the car was released back to the customer.
The bumper was quickly installed and I went back to the highway and it was like night and day. The Blind Spot system was now working as designed and it was no longer blind-sided by the vehicle body while driving down the road. What a roller coaster ride this vehicle turned out to be. It was nothing real technical, but rather a “thinking out of the box “moment. These are the type of jobs that a normal text book is not going to find because this car entered the “Twilight Zone” where nothing could apply to its fix. It is always good to keep open minded and be very visual in your Diagnostic Interrogation process. I just hope this story will hit home with a lot of you body techs out there and help you to understand how critical it is for radar module installation procedures.
