Unfortunately, there appear to be more reckless drivers on the road nowadays. The goal of this guide was to share my experience with a blind spot system that proved useful, particularly when we encountered unsafe drivers (i.e., distracted, aggressive, selfish, and so on). As you will see further down, the W203 chassis requires a simple modification to the inner rear bumper to accommodate both radar sensors. Of course, it will differ depending on the product purchased and the configuration of your rear bumper.
WARNING
Since this involves modification of the electrical circuit, please be careful to prevent any injury or even car damage.
WHICH TO CHOOSE
Each car brand has its own jargon, but they all serve the same purpose. As more and more newer cars come equipped with this safety feature, I've been considering installing one to step up my game on the road with the good old W203!
I purchased an aftermarket product from Driintel on AliExpress in 2021 but did not install it until the summer of 2022. It was their most recent 77 GHz BSD product, which is said to outperform 24 GHz. Unlike the others, their product appears to be the only one at the time with bundled BSD-enabled side mirrors for the W203 chassis, giving it a nice OEM look.
Before purchasing, the sales representative requested photos of my side mirrors to ensure compatibility. I was initially skeptical because there were few online reviews. In 2021, the price without shipping was around 533.44 CAD. In comparison, a single Mercedes radar sensor would have cost in the same price range.
PRODUCT PACKAGE
[2] LED side mirrors (either a red triangle [purchased] or a yellow 2-car icon). Because it is slightly convex on the outside, it has a wider field of view (FOV) than the originals. Theirs could be heated but not dimmed. Because the dimmable ones were out of stock, I had to settle for the non-dimmable ones. Unfortunately, without an auto-dimmable mirror, the glare is noticeable at night, so keep that in mind.
[2] 77 GHz radar sensors, each with two trigger lines (line 1 and line 2). I wasn't sure which line to hook up; tech support said either line 1 or line 2 would suffice. I believe it is for a dual warning system (1 outside and 1 inside on the A-pillar).
[2] Stainless-steel mounting bracket (not used)
[2] A rigid, serrated, flexible conduit protects the extension wire harness. The clip-on connectors are completely waterproof.
[1] Piezo buzzer with one end connected to a connector
[1] A triangular-shaped paper template for determining the proper angle
[1] round, small bubble level
[1] English photocopied manual and three installation videos were emailed to me after the purchase.
MATERIAL AND TOOLS USED
[1] Mercedes side mirror screwdriver (to remove the mirror completely from the chassis) HAZET 2715-20H or comparable
[1] Utility knife (for cutting through the plastic on the inside of the rear bumper)
[1] Drill (to make screw holes)
[1] Fuse Holder Add-a-Circuit *standard ATO size (not mini) (Fuse #7 is reused, another 7.5 Amp fuse is required)
[1] Heat-shrink tubing (to keep water out) wire harness cloth tape (to keep wires together while reducing noise and wear)
[1] Soldering iron or crimping tools (both useful if used correctly)
[1] Room-Temperature-Vulcanizing (RTV) silicone (to seal around wire entry points on side mirror rubber seals and trunk grommets).
[1] Optional: 12 V reverse camera stabilizer (1000 uF) (to keep 12 V stable if it fluctuates).
[1] OBD2 tools, MB Star C3 or C4 (to clear noncritical fault codes caused by side mirror disconnection), are highly recommended.
INSTALLATION
I've included a Mercedes WIS (Workshop Information System) document for side mirrors, rear bumpers, front door side panel, and so on for disassembly and reassembly instructions.
STEP-BY-STEP SUMMARY
1. Put on your authentic Mercedes-Benz white cloth gloves (for both style and safety).
2. Remove the trunk trim panel (to gain access to the rear bumper bolts).
3. Remove the rear bumper (in order to gain access to the inner bumper cover).
4. Repair the radar sensors by modifying the rear bumper.
5. Drill holes in both grommets to pass each wire through, then seal with RTV silicone.
6. Attach the two radar extension wires to the harness.
7. Attach the piezo buzzer to the wiring harness.
8. Reassemble the rear bumper (with the help of a stool).
9. Construct the add-in circuit and locate the ground screw (as shown in the photo).
10. Remove all four door molding strip panels (to conceal both side mirror wires).
11. Disconnect the side mirror assembly from the chassis (*special screwdriver required).
12. Install new BSD side mirrors.
13. Take off the interior door trim panel (to fish wires inside the vehicle).
14. Solder or crimp trigger line 1 to turn the signal line (cover the exposed end of line 2). To prevent shorts, wrap exposed metal in heatshrink tubing.
15. Apply RTV silicone around the wire hole on the side mirrors rubber seal.
16. Re-assemble the side mirrors.
17. Remove fuse #7 from its original socket (rear fuse box) and place it on the Add-In-Circuit before inserting the Add-In-Circuit into the fuse #7 socket.
18. Take it for a test drive.
I'll go over them in greater detail in the sections that follow.
REAR BUMPER
Like the latest Mercedes-Benz, the radar sensors will be installed on the inner plastic bumper shell. There may be no metal or reflective tape in front of the radar sensor; only plastic is permitted. We cut the plastic part of the bumper just enough to allow the radar sensor to pass. Please see the photos for a better illustration. Drilling two holes per sensor from the inside of the rear bumper (plastic outer shell, not steel inner rear bumper like in their videos) on an angled recessed plastic molding (refer to photos). I used the provided paper template to measure the angle, which is 20 degrees outward in my case.
I should have used blue Loctite on the screws to prevent vibration loosening, but I didn't. Unlike the instructional video, I did not install the steel bumper because there is insufficient clearance between the outer plastic shell and the reinforcement steel bumper on the W203. You'll notice that I had to make a larger hole to access the sensor. I highly doubt structural integrity was harmed by the removal of a small amount of ABS plastic near a hole.
I'm not sure if the Parktronic sensors in the rear bumper will block the BSD radar sensor because I don't have Parktronic. We connect the reverse trigger to the reverse light (for reverse camera wiring instructions, see the W203 forum). I chose the right side because I already had that line tapped in from a previous backup camera trigger line. The wire from the radar sensor is routed through a rubber grommet (see photo). It's probably for Parktronic wire. The rest of the wire extension can be found inside the spare tire compartment. If you want, zip tie it for cable management.
SIDE MIRRORS
To connect the trigger line to the side mirror LED light wire, you must first remove the entire side mirror assembly with a special long screwdriver. For wire connections, I prefer soldering, but some people prefer crimping. For an overview of the wiring diagram, please see the image. Both extension wire harnesses exit the trunk and travel under the door molding strip panels on each side of the car. Simply pull it up with a trim tool to remove it. To access the side mirrors, I recommend removing the door panel and fishing it through the rubber conduit for a cleaner look. A fishing technique similar to in-wall wiring installations can be used.
I use an add-on circuit on fuse #7, which is backup relay 1 (N10/2kD) 7.5 Amp, to power the system. This fuse is in the trunk's rear fuse box, on the inner left side. This fuse will not drain the battery when the car is turned off because it only works in ignition position 1. When the car is turned off, for example, fuse #3 (Parktronic dome light) and fuse #6 (spare) appear to be constantly on. The add-in-circuit's holds two 7.5 Amp fuses, leaving backup relay 1 unaffected from any shorts originating from the base unit.
***
You must establish which of the two fuse box contacts has power. The add-in-circuit contains a single power contact, which may change depending on the model. Check that it is properly positioned. To be safe, insert the add-in-circuit without the stabilizer first. The item will power on once the right orientation of the add-in-circuit has been determined.Otherwise, it will just not work. Disconnect everything; you may now add a stabilizer if desired.***
How do I know which fuse to use?
Knowing what it is for isn't enough in this case because some wires have a constant 12 volts even when the car is turned off, which we don't want. We must test each fuse while the car is turned off without prior knowledge of this information. Constant and switched fuses can coexist next to each other. I tested by connecting a multimeter and placing it on the back seat, where I could see the voltage value through the window. I choose a fuse that drops to 0 volts after locking the car (for the shutdown process); this is our switched fuse. Please see the rear box fuse pdf for more information.
STABILIZER
In case the voltage drops or fluctuates while driving, I've installed a stabilizer between fuse #7 and the BSD. Please keep in mind the importance of correctly connecting both wires (red and black) by following the direction of the arrow indicated on the stabilizer box ("out" goes to the BSD). Otherwise, you risk damaging the capacitor, which could explode and start a fire. To waterproof the 1000uF capacitor and prevent any potential shorts caused by water exposure or condensation, I injected black RTV silicone inside the plastic box containing it. When compared to using an epoxy resin waterproofing material, it can be easily removed for troubleshooting.
POST INSTALLATION
There is no need for calibration. When the ignition is in position 1, the LED on both side mirrors flashes twice to indicate that everything is in working order. I suppose keeping the rear bumper clean is a good idea.
LINE CHANGE ASSIST
Certain speed conditions must be met for it to be alerted, just like any other system with Line Change Assist. You cannot, for example, walk in front of sensors and expect them to sound an alarm. I tried it just for fun because I wanted to ensure that it worked before installing it. I did trip it once by running Amok at an angle into the sensor.
The piezo buzzer sound chime is quite loud and often startles the passenger. I'm considering implementing a custom audio sound with volume adjustment (similar to those customizable electronic kits found on a birthday card) or, even better, haptic feedback (as found in a cellphone). For the time being, I've hidden the speaker behind the driver's seat. This BSD system appears to work well even in bad Canadian weather (rain and snow).
REVERSE CROSS TRAFFIC ALERT
RCTA works when reversing into perpendicular incoming traffic.
ANGLE OF ATTACK
For example, if you backup at high speed into a rear obstacle on the left or right, regardless of the status of your turn signals, an audio alert will sound. At slow speeds, there appears to be a false positive for either AOA or LCA.
For example, when turning (with a flasher on) at an intersection in the city to engage a double-line road (you take the outer lane) (the driver behind you takes the inner lane and overtakes you). As a result, his car will hit your blind spot, triggering LCA or AOA, because the radar sensor predicts a linear motion, implying that it will hit your car. However, both cars are turning on the same curve at the same time, one slightly behind but slightly faster than you. In this scenario, I believe the BSD did not properly filter out non-linear motion in the tracking/prediction algorithm, though I could be wrong.
FALSE POSITIVE
It appears to happen when slowly turning into an intersection or a parking lot with the flasher on and a car driving by on your tail. It will generate an alert as if it were confused by a possible angle of attack scenario. Similarly, it appears that I am not the only one experiencing this; an online customer review on AliExpress mentions it as well. To avoid this, simply turn off your turn signal as soon as you reach the curb, or simply do not signal when turning in the city (obviously not recommended).
Perhaps we can design a circuit that disables this type of warning (LCA, AOA) at slower speeds while increasing the minimum speed from 10 km/h to 60 km/h, as Mercedes-Benz does. There is, in fact, a fine print in the manual about wiring the speed line, but this unit did not have it. In any case, the calculated algorithm is likely to be far more complex than I can imagine.
FUTURE
First and foremost, I have no idea how long this radar sensor will last or whether its accuracy will degrade over time. It has worked flawlessly for over a year, including during the winter. Fortunately, the radar sensor is located so that it gets protected by the rear bumper reinforcement structure located just below. The radar sensor housing is well-made and does not have a cheap feel to it. Because the wire is enclosed in a plastic conduit, it is well protected.
The plastic back cover of the side mirror appears to have been manually cut off in order for the LED to flash through the glass. In fact, they sell LED replacements. According to what I understand, they can custom-make from OEM glass using an in-house laser-cutting tool. I'm curious how this will affect the mirror's dimmable function.
Furthermore, with the proliferation of automotive radar on the road, it is unclear whether interference with other similar radar sensors will occur and how this will affect its performance. Meanwhile, this ADAS upgrade has saved my butt more than once. The best part is that your wallet can stay in your pocket. To activate this feature, there is no monthly Mercedes-Benz subscription fee!
Take care, and don’t forget to... Check your blind spot!
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