2002 Mercedes A-Class Parking Sensors

Grant Tiller

This was posted on a Mercedes Forum many years ago – I have been asked to re-post, as the article and pictures have long since disappeared.

The original article had a few thousand hits, so I guess there is still demand for it!

Fitting a Reverse Parking Aid to my 2002 Mercedes A-Class (A170 CDi) 

This was a very simple job that took only a couple of hours to complete.

I used the four sensor parking aid called Parkmaster 4 by Cobra.

I spent some time researching what was considered the most reliable and best quality.


I purchased the unit from www.incardiscount.co.uk

The unit cost £100 all in.

The Cobra was the best compromise of price vs. quality and has received many positive accolades by the aftermarket specialists.


The Cobra kit came with very clear and concise installation instructions in a multitude of different languages.

Grant Tiller

Manuals, drilling templates, warranty – in all European languages

Grant Tiller

I used this as a chance to give the rear of the bumper a good clean

Grant Tiller

The close ups here show that there are four markings on the rear of the bumper for the factory fitted sensors

Grant Tiller
Grant Tiller

Drilling for the sensors – i first drilled a very small pilot hole from the rear of the bumper using the markings kindly provided by our friends at Mercedes Benz!

Grant Tiller

With the holes drilled, I could attach the self adhesive templates provided.

The reason for this is that you must drill a 2mm diameter hole (numbered 2 in the diagram) on the edge of the large hole.

This enables the ultrasonic sensor to locate nicely, and not swivel in it’s hole.

Grant Tiller

And now for the scary bit – using a holesaw to cut the large hole.

Grant Tiller

Be careful to drill at the correct speed (not too fast) as we don’t want to melt the plastic.

Grant Tiller

Similarly don’t go too slow, as we want a nice clean finish to our hole.

Grant Tiller

If you need to, clean the edge of the hole with some fine sand paper. 

Grant Tiller

With all the plastic blown away, we can now reassemble the bumper.

Putting the foam insert in place first, and then clipping in the Ultrasonic Sensors

Grant Tiller

Once again our friends at Mercedes Benz have kindly left grooves in the foam insert for us to route our cables!

Grant Tiller

I loomed my four sensors, as it makes life a lot easier, and things tidier.

Simply measure out where the sensors are positioned and then wrap pvc insulation tape around the cables – this will keep them all together, and help them stay in the groove of the foam insert.

The sensors have waterproof rubber boots on them to prevent ingress of dust, dirt and moisture.

I liberally spread some silicone grease around the boot after fitting it, to help keep out the elements!

Grant Tiller

Now offer the bumper up to the rear of the car – you will find two unused rubber grommets on the left hand side of the car in exactly the right place!

Pierce a hole in the grommet, and push the cable through (it is easiest to remove the grommet to make the hole)

Grant Tiller

I then refitted the grommet and used some silicone sealant around the hole, to ensure moisture doesn’t sneak in.

Grant Tiller

There are plenty of places to site the piezo buzzer.

I screwed it to the high density foam block between the cubby hole in the rear quarter panel and the air vent just below the rear window.

That way, it is completely out of site, but very easy to hear.

Alternatively Cobra provide self adhesive pads so you can stick it anywhere in or around the boot area.

Grant Tiller

Once again, I made the cables into a loom.

This is not a necessity, but I think it makes thinks look tidier and more professional.

… this time I used some foam tape, as the cables were to be placed in the cavity between the skins of the rear section.

I used foam tape to stop the cables from rattling around in the cavity.

Grant Tiller

Plugging the control unit in is very simple. Just match up the letters and numbers!

When it is connected, poke the unit back through the hole in the rear cavity.

There is a large piece of sound proofing sponge already in this hole – you can jam the control unit in here to stop it from rattling.

Grant Tiller

There are two connections for power – there is an earth stud near the rear light cluster.

Grant Tiller

The positive cable then attaches to the reversing light wire in the rear light cluster.

This is easily located by taking out the reversing light bulb, and following along the track.

Grant Tiller

Here you can see that all the cables have been wrapped in pvc tape.

Its worth mentioning that Cobra provide a Scotchlok cable fastener that allows you to easily tee off the positive power connection from the reversing light.

I am not a fan of these fasteners, so I soldered the cable in-line instead – this is much preferred, as it provides a stronger and more reliable connection.

Grant Tiller

With the control unit and all the cabling neatly installed and hidden away, I can begin to put the inside of the boot trim back together.

Grant Tiller

The finished article – the factory fitted ones are finished in the same colour as the bumper, but I think they look fine in black.

The Cobra kit comes with detailed instructions on how to paint them if you wish.

Grant Tiller

With everything in place, all I need to do is calibrate the system.

This is easily done by reversing up to a brick wall.

Park a set distance away (as determined in the instructions) and then cut the blue cable that plugs into the control unit (which I left neatly coiled up by the light bulb holder, so it is accessible through the carpet flap)

If you every need to re-calibrate (i.e. if you have a towbar fitted) you simply cross the two cut wires.


THAT’S IT – easily done!

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