Rear Parking Sensors

[Stanley]

Good Afternoon.

At the risk of sounding like a numpty, can anyone advise me on when the rear parking sensors kick in?

I have only had my car for a week and I am happy to accept the issue could be me, so here goes.

When the car is in park and I select reverse I get one short beep followed by a continuous one.

However, when I select reverse after being in drive, I get one short beep and then the sensors work.

I have tried putting the car into neutral then reverse and get the continuous bleep.

Any advice or ideas?

 

In every other auto I have driven with parking sensors they worked when selecting reverse from park?

 

[James]

Sounds like you have a fault with the sensors to me. The sensors should always work in reverse.

[Stanley]

Thank you, I tend to agree with you but have taken the car to auto electricians and they cannot find any fault. It only seems to be an issue when staring up and selecting reverse for the first time, i.e. not going from drive to reverse. After any long journey they work as they should do? Thisd presensta  problem as when driving somewhere to have them looked at I can never replicate the fault?

Someone did suggest it may be a bad earth?

[James]

So if you put it into drive first after a cold start and then reverse they work ok?

[Stanley]

I have had all four sensors replaced and once the car is warm there is no audible beep other than selecting reverse.The problem seems to be when staring up first thing in the morning.

I turn they key engage drive then the OK sign appears, I drive off no problem.

If however my first direction is reverse after I engage reverse, the first beep tells me I am in reverse, this is followed by a long continuous beep .The sensors do still seem to be working though, or do now I have had them replaced.

I have tried putting into drive then neutral then reverse, sometimes this cures it sometimes not?

Whilst checking once without the engine running I do recall seeing and image of the car with reverse sensors showing as a solid red light pushing out from rear of car but have never seen this appear again?

 

[James]

Just a thought - might be worth plugging it into VAGCOM to see if there are any fault codes stored? Might point you in the right direction?

[Stanley]

Thank you, I have done that, it showed a fault in one, the place I bought the car from replaced all four but i still get the same issue, sometimes not for days. The reversing lights come on so the message is getting there from the gear lever. I am intrigued by the image on the dash of the car with beam emanating from the rear of said image but can only replicate this image with engine off and even then only one in 10 . Should this red image show up each time reverse is engaged? only when something is in range? I cannot find any reference to this in the manual.

[Brucielee]

Can you get access to the sensors wiring, I was going to suggest unplugging them one by one to see if there is one of them that maybe has a bad wire that's causing the fault, I'm not sure if they work independently or as a one, I know you said they are all new sensors, but fractured or corroded wiring is always a possibility, and not sending the information, which could be why and it sounds daft that it's working OK after you drive and warm up, which could be also why the auto sparks couldn't find a fault, 

[Stanley]

Thank you, the only access involves taking the bumper off. From what I can see the wiring harness is all in one piece that plugs into the control unit.My guess would be that is the problem only because when the sensors work there is no display on the dash. It is a bit like going to the dentist with tooth ache, each time I take it to a garage they work when I drive away they do not.no faults are ever displayed as the sensors do all be intermittently work.

 

[Brucielee]

That would be my first port of call Stanley, see if you can source a wiring loom cheap and change it, I had a bad door wiring loom and it worked intermittently while driving, the conclusion was that the vibrations of driving were making a bad wire connect and disconnect, I know it's not sensors but you'll maybe find that the wiring is doing something similar, hope you get it sorted, 

[James]

Let us know how you get on Stanley 

[Stanley]

Right, I had the wiring checked and all was ok so went for broke and got a new control unit. Drove 130 miles all ok on outward journey, stopped on way back to get something to eat and hey presto another fault ! When selecting reverse I got the initial bleep followeed by some rapid repeating beeps, nothing behind the car. When moving of the rapid beep became a continuous one.

Tried again this morning and no problems at all.

I guess the only thing left to swap out is the wiring? I have not been able to find one for a B7 yet but will keep looking.

Someone did suggest that over painting may also be an issue?

The garage I bought the car from sourced some replacements, and had them painted, I went to collect the car and they had been painted the wrong colour so the garage went to Halfords and bought a spray can and painted them again.

In my mind this could mean that there are at least three layers of paint on the sensors.

I know this should mean that they would not work at all but..................

[James]

Thick paint on the sensor wouldn't show as a fault, they would either not pick up anything or beep like crazy thinking you're touching something.

[Stanley]

After much deliberation and several auto electrician visits, the consensus of opinion is that my rear sensors have too much paint.

I am guessing that the sensors sourced by the garage were not new so assuming they were painted to match that would be two coats?

They admitted to painting them the wrong colour so added another coat.

I spoke to the Audi dealer where the car was first registered who confirmed that if too much paint the slightest increase be it dust rain or salt would cause the sensors to react as if close to an object.

This conclusion was reached recently when after a long drive where the sensors worked at the start they stopped after parking up. On close inspection one sensor had one rain drop on it which gave the impression of being close to something. With the car in reverse and handbrake on I wiped the sensor and the continual bleep stopped.

It does not help that I live next to the M275 so my car is covered in dust most mornings, But so far this week cleaning the sensors before moving off seems to work. This is not an ideal solution but it is a start.

[James]

Looks like you could do with sourcing a new set of sensors then?

[Stanley]

Thank you, i have sourced some from Germany and will have then fitted without re painting to see if that cures the issue. I am guessing that this may have been a long standing problem as when i had them checked before, the four that are fitted now were not identical so could have had multiple layers of paint on them. 

[James]

20 hours ago, Stanley said:

Thank you, i have sourced some from Germany and will have then fitted without re painting to see if that cures the issue. I am guessing that this may have been a long standing problem as when i had them checked before, the four that are fitted now were not identical so could have had multiple layers of paint on them. 

Sounds like a good bet. Let us know how you get on when they arrive! How much did that set you back from Germany?

[Stanley]

Good Morning

Sorry for the delay. The sensors I sourced from eBay that said genuine parts made in Germany actually came from Poland and cost £10.79 each.

They looked identical to the first set of sensors the garage replaced, and nothing like the ones the garage fitted.

I would like to believe the painting or over painting was the issue all along so I am loathe to have the new ones painted.

For reference the ones I purchased were Parking Sensor PDC AUDI A3 S3 A4 S4 RS4 A6 S6 RS6 - 7H0919275A

http://www.ebay.co.uk/itm/271890597029?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

So, as it stands I have the four sensors the garage took out, one of which had failed, it would be too easy to say that the one that failed was 7H0919275B and the four that they replaced them with.

i doubt there is anyway to check each sensor or to clean them but if anyone thinks they can then feel free to contact me.