Parking sensor kit wiring

[kilou]

Hi,

thanks to you on the forum I have been able to solve the problem with my car not starting after installation of a parking sensor (the battery was drained). Hence I start a new topic here because I have a question on an alternative way to wire the parking sensor kit.

Basically the parking sensor kit is powered by a 12V controlled by ignition (terminal 15). However to sense when the unit becomes active, it is also linked to the positive reverse light cable (to activate both front and rear sensors when reversing) as well as to the positive brake light cable (to activate front sensors when driving ahead). My system is correctly triggered when the reverse gear is engaged but it doesn't work when the brake pedal is depressed although the brake light work. The wiring is correctly installed and has been checked but it appears I may have a defective unit that is not triggered by brakes.

I thought then about an alternative wiring solution to this problem. As the reverse light is able to trigger the parking sensor kit, all I would need is to install a switch so that the parking sensor kit can be triggered by either:
- selecting the reverse gear (this works yet)
- press down the switch

In order to achieve this, I thought about connecting that switch to a 12V continuously providing power. Please look below for a little drawing of the wiring I suggest.

This wiring would trigger the system:
- when the reverse gear is selected (12V provided by the red wire)
- when the switch is pressed down (12V provided by the green wire)

My questions are:
- will this wiring scheme work as descibed?
- what will occur if the reverse gear is selected while the switch is pressed down????? This would cause two 12V cables (red and green) to be linked one another!!!! Is it a problem?

Many thanks for your help

 

[chas3]

i suppose it will work.

when you press the button your reverse lights will come on even if you are not in reverse. you could put a diode in series with the connection to the reverse light signal to prevent this:

sensor box ---- button splice --- |
radioshack should carry a 50V/1A diode that would be plenty.

however, what is wrong with the brake signal? usually, the brake pedal switch grounds the circuit; so you see 12v unless someone presses the pedal and then you see 0v. its something like:

+12v ----- LAMP ------ PEDAL/SWITCH ---- GND

what does the parking sensor expect to see? is the volvo brake wiring different?

 

[kilou]

Actually the parking sensors are enabled either by the positive 12V for reverse light (for reversing) or by the positive 12V for brake light (when going forward).

As far as I could see, the Volvo brake pedal is not grounding the system when depressed. Once the pedal is pressed down, there is 12V reading at the brake light. I assume when the brake pedal is pressed down, the brake pedal switch closes the circuit so that the 12V can reach the brake light. At least this is what seems to be shown on the wiring diagram: the pedal switch is on the 12V line, not on the ground. Does this make sense?

The brake signal of the car is OK, I believe there is only something wrong inside the parking sensor controle module. In fact after depressing the brake pedal, the LCD screen of the parking kit should light up and the front sensors should get active AND these sensors should remain active for 30 seconds. The problem is that when I depress the brake pedal, the LCD screen lights up for 1 seconds and then goes off so I assume there is some problem with the "memory" that should hold the sensors active for 30 seconds. I believe that maybe I "burned" something in the control module when I plugged incorrectly the cables

This is why I'd like to solve this problem by using that switch to manually activate the system when driving forward.

You're right about the reversing light poping on when the switch is pressed! I've not thought about this

But if I use a diode to prevent this from happening, I guess the diode will also prevent the parking sensor to be triggered by the reverse light no????

 

[kilou]

And what about this wiring scheme with a 2 ways switch:

When the switch is on position 1, the control module is triggered by the green 12V cable (manual triggering).

When the switch is on position 2, the control module is triggered only if reverse gear is engaged (reverse light on).

This setup should avoid any problem no? The only problem I can think of is related to the earth wire on the reverse light. Imagine that the switch is on position 1 (system triggered by the green wire) and that the reverse gear is selected. In that precise situation, the earth wire of the reverse light would serve both to return current from the reverse light and to return current from the control module. Will this cause any problem??

Another question:

Since the control module has its own power supply controlled by ignition (blue wire), I guess the other 12V wires such as the red and green ones are used to trigger the system but no current is drawn through them. I assume that the control module has built-in voltmeters which sense if there is a 12V voltage between the earth and the violet wire. If there is a 12V voltage then the system becomes active but it is powered by the blue wire only no? If this is true, this means that no current (amperage) is going through the violet wire at any time and thus I do not need to install any fuse on this wire. Correct?

[ April 19, 2005, 04:06 PM: Message edited by: kilou ]

 

[chas3]

a diode allow current to flow in only one direction.

the signal voltage at your brake switch can be +12V. if could be the other way around though. automakers do strange things. if the wiring diagram says it switch +12V and not ground then that is what it does.

your latest circuit would seem to fine. i would not expect to get any "leaking" through the sensor to the purple wire. you can probably wire your switch to the switch ignition wire instead of the continuous power. does not make much difference since the module will only run when it has power.

so the sensor has two inputs: reverse and brake. are both supposed to activate all the sensors? i can understand the lcd only running when the brake pedal is depressed. with an auto transmission, parking you almost always have the brake depressed when going in the forward direction. however, yo u could wire both the brake and reverse 12V inputs to the reverse input using diodes. two diodes can be used as an "OR".


+12V brake ------>|-----O------|
O would be where you get the or'ed signal from the brakes and reverse lights and feed the parking sensor. without the diodes you would get reverse and brake lights when either was powered.

 

[kilou]

OK I thought the diode would "eat up" all the current but as you said it will prevent the current to run in only 1 direction. However I prefer the design with the 2 way switch for the followig reason: with the brakes triggering the parking sensors in forward direction, this would mean that the LCD screen will always light up once the brake pedal is depressed, even when slightly braking on the highway for example where you obviously do not need the help of parking sensors

This is why I prefer to have the ability to manually switch on the parking sensors in forward gears. On the other hand, the sensors are still "automatically" activated once the reverse gear is selected.

Both triggering method (either by selecting reverse gear or switching to manual) would activate both front and rear sensors. The original design with triggering by the brake pedal would have triggered only front sensors in forward gears. This is because the brake pedal triggering use another wire than the reverse light triggering. In reverse gear, all 8 sensors would have been activated but the front sensors should have remained active for 30 seconds after the reverse gear was disengaged. This is actually this 30 seconds countdown that doesn't work on my system, supposedly because I must have frozen something in the system by making wrong connections in the beginning...

Anyway, I try today the design with the 2 way switch and as you proposed, I'll use the blue wire (12V on ignition) to power the sensors AND as replacement of the green wire. I'll let you know how this works, hopefully tonight.

Thanks again for your help

 

[chas3]

quote:

---

Originally posted by kilou:
with the brakes triggering the parking sensors in forward direction, this would mean that the LCD screen will always light up once the brake pedal is depressed, even when slightly braking on the highway

---

i guess that might be why the brake signal only works momentarily. it would be annoying to have the parking sensor turn on for 30s every time you touch the brakes.

 

[kilou]

I finalized the installation and everything seems to run perfectly

The switch is working without a hitch and activate the sensors when I need them otherwise the reverse gear triggering method still works fine.

I find this to be much more convenient than to trigger the system with the brake pedal. Indeed, I test drove the car on the highway today and switched on the sensors at 120km/h to see if they read anything. What a surpise: they were all flashing and the sound was omnipresent in the car despite the lack of any object in the neighborhood......better like this on the highway no

I guess this is done by air turbulences fooling the sensors in thinking there is a nearby object as the sensors work with pressure difference. The conclusion of this is that if I had used brake pedal triggering method, I would have had sensors flashing and sounding every time when braking on the highway..........not very oprimal! Now with the switch the problem is solved

As you said Chas3, I used the blue wire to provide the 12V to the switch. This works fine and it was easier to do so because the blue wire was closer to the switch.

There is only one thing left that I must understand a little further: it seems that when the system detectes objects, even switching it off or disengaging the reverse gear doesn't shut down the sensors. In that case, I have to turn off the ignition. However when the system doesn't detect object in the neighborhood, it can be shut down by the switch command or by disengaging the reverse gear. Strange but nor a problem at all.

Anyway, I'd like to thank everybody on the forum and especially Chas3 for the help provided that was very very helpful for me because I do not understand too much things in electricity. Thanks agin!