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Rostra Obstacle Sensing System

Author: Alex
Date: Mon Jun 16, 2003 12:37 pm

Mazda MPV is a big vehicle and it requires to be very cautious when reversing. It might be a challenge to ensure that there's nothing in your way. That's why I decided to install a back-up aid. After looking into some models available I chose to go with Rostra Obstacle Sensing System (ROSS) because the sensors can be placed behind the plastic bumper which doesn't require drilling any holes in it.

Anyway, I ordered the unit from Automotive Safety Technologies. Sure enough the package was delivered within a week as promised. Installation of a ROSS unit isn't difficult if you know where to mount all the components and how to run wires. I hope these instructions will make it simpler.

The package contains almost everything needed to install the unit.

Additional instruments needed: Drill, 10 mm wrench or drill attachment.

The contents of the package. A control module and two microwave sensors are the heart of the system. Sensors are mounted behind the bumper on a special mounting brackets. The original kit comes with generic brackets that can be cut and bent for the MPV. However I ordered pre-bent and cut brackets (for US$5) so I don't have to deal with the hassle of doing this myself. However on a second thought, it would be very easy to do it myself. If you decide to cut the bracket yourself, cut it a little more than specified in the manual. When done as suggested, the bracket appears to be a little bit too long to fit behind the bumper. I had to drill out the bolt holes in it to make them wider.


Mounting position. The two sensors are placed behind the bumper at the point where the bumper fascia is bolted to the body.


Bumper fascia mounts. The two mounts to which ROSS sensors are also attached. As viewed from passenger side of MPV.


Installing the passenger side (right) sensor.

1. Remove the outboard 10 mm bolt.


2. Attach the sensors to mounting brackets using supplied 10 mm bolts, nuts and serrated washers. You might want to cut additional 5 mm off the brackets because sensors still seat too far even if you slide them completely in.


3. Place the bracket on top of the bumper mount and use the same MPV bolt to attach the bracket. Make sure that the sensor faces the rear of the car and is parallel to ground (it should be OK if you bent the brackets correctly or if you use the pre-bent ones). Also make sure the sensor is flush with the bumper fascia. If it is not, release the 10 mm bolt holding the sensor on the bracket and slide it to proper position.


4. Drill 5 mm hole as shown.


5. Using self-tapping bolt supplied in the kit, secure the bracket to van's body. The bolt is covered with glue-like resin, so when it is screwed in, the resin seals any gaps. Cool Smile


Now one senor is mounted. Repeat the same steps for driver's side (left) sensor.

Installing control module. That was one of the biggest challenges. The manual doesn't state where to place it. I didn't want to drill any more holes, so I mounted the module on the bumper itself. It has a hole right next to its mount. I bolted the control module using kit-supplied mounting bolt (the long one). Note, mount the module on the left side of the van (driver's side) otherwise the wiring harness will not be long enough to route it inside. Now cut the mounting bolt close to the nut so it doesn't stick out.


Secure all the wires underneath the bumper by using the supplied plastic straps.


Routing the wiring harness inside the van. Now, that's a challenge! Again, the manual doesn't say how to do this. And from what I've discovered, Mazda didn't leave a single hole in MPV's body unsealed. Everything is sealed with polymer rubber... I guess MPV will float on the water Smile Anyway, I found the air vent in the jack area. It is covered with rubber stripes (like horizontal window blinds). I guess that's where the air, sucked by HVAC, goes outside. That's the only way I see to put the wires through inside without drilling new holes or removing sealing from existing ones. Route the harness from control module around the corner between the bumper and the van's body. I actually put another wire from the jack compartment outside, then tied the harness to it and pulled everything back inside.


Now connect power to the unit by using supplied tap-in connectors. Attach ROSS's black wire to the black wire going to the left rear combination light (in the jack compartment right after the connector. ROSS's blue wire should be tapped in to red wire with green stripe. This is the power to reverse lights. Connect the audio control unit and LEDs, put the transmission in reverse (without starting the engine) and test the sensors by approaching the vehicle from behind.


I didn't put the audio module and LEDs in suggested location on the rear hatch for two reasons:

  1. The wiring harness seems to be too short and needs to be extended
  2. The beeper isn't loud enough to hear from the front of the van when the stereo is playing.
Therefore I'm planning to move the audio control module to the front and place it behind the dashboard. While I'm still going to mount the LEDs onto the rear hatch glass as suggested in the installation manual. It will be my next project. So far the audio module is lying in the jack compartment and seems to work just fine. I will post additional instructions on how to place the audio module in the front and the LEDs onto the rear hatch. Stay tuned...
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