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Discussion Starter #1
Hello all

Needed a larger car for the little ones. Got rid of my Honda and got a second hand 2010 Cmax. 1.8 tdci. With 60000 on the clock. So far so good a few niggling issues. On the center dash under the hazard lights there is a parking sensor button. Above that there is the word on. It keeps flashing all the time. Parking sensors on the rear work fine but not on the front so guessing somethings wrong there.

Washed the car yesterday and had some rain after and sadly there is mater in my boot. The to white bits of trim that the seat belt passes through in the boot, at the base of these was a little water?

Hope I can get these little bits sorted.
 

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Hi, welcome to the forum.
I understand the dashboard switch is only fitted to cars with front sensors. The switch turns all the sensors on, as the front ones don't work on their own. The gearbox reverse switch also turns them all on.
They only work at low speed, once on they stay on until you reach 10mph, or turn them off with the switch.
There's a high pitch warning tone for 3 seconds if a malfunction is detected so that can be ruled out.
If the light is flashing it could be a fault with the switch, if you press the switch does the light stay on? Does the light come on and stay on in reverse?
There's only one control unit but there are 2 sounders, one at the back and one in the dashboard. So the sounder could be at fault, as you say the back one works.

I had front sensors on my last C-Max but never had any issues. I didn't have any water leaks either, but my first C-Max had to have a new roof lining because there was a leak in the roof joint. I don't recall exactly where the water showed, but it was toward the back and could have been where yours is showing. The mechanics (this was 2003, before they were called technicians) damaged the roof lining taking it out the second time after the first attempt at a repair didn't work.
 

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Discussion Starter #3
Thank you for your response.

So basicly when I start the car there is a tone for 3 seconds then stops.

The light flashes constantly, doesn't matter if I push the button or not it doesn't seem to do anything.

A friend threw a laptop on it and the code that came up mentioned power supply no ground or something. So he thinks it could be a fukt in the wiring or a sensor.

So just to be clear so I understand
My back ones work and activate when I put it in reverse.

My front ones if they was working I'd have to press the button first and the on light would come on?

I've never seen the on light on solidly it's always flashed so far.

With the water in the boot going to check the rear light seals
 

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You're correct with the way the sensors normally work.
The 3 second tone is to alert you to the fact that the system is detecting a fault. If it stayed on it would be irritating to say the least. And the flashing light is an extension of the alert.
I misunderstood the flashing to be a random flicker.
So we know the malfunction is definitely with either the front wiring sensor loom or a sensor.
Maybe you can try unplugging each of the sensors one at a time and see if the fault is still there?
 

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Just an additional note, the front sensors do activate at the same time as the rear with the reverse switch.
The rear ones activate at the same time as the front sensors with the dashboard switch.
So they all work together, so for example if you're driving into a parking space you can switch the sensors on without selecting reverse and similarly if you don't want them on when you're in reverse you can turn them off.
I'm sure I've made it sound more complicated than it is but it just works.
When it's working.
Good luck with the fault finding.
 
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