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The case of the blind-sided Jeep

Monday, May 27, 2019 - 06:00
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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.

Figure 1

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.

Figure 2
Figure 3

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.

Figure 4

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.

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