2007 e70 3.0d SE Parking sensor system failure

[minesapasty]

I have had the car for over 12 months and she has been lovely, no issues at all, except for driver error for not being totally up to date with how things operate..... I tend to learn as I go, I've never been one of those "read the manual before touching", pfffftttt where is the excitement in that ?
Anyway, yesterday, all was well, other than the car reminding me that an oil change and rear brake check are due in the near future (she has already been booked in for my "tame mechanic with a ramp" to sort these), but this morning, out of the blue I have a warning telling me that I have a parking sensor system failure..... where did that come from ??? I thought to myself, so I started searching, then the site said that I couldn't search anymore
Is a single parking sensor likely to announce a total system failure, or is it going to be an ECU somewhere ? Any thoughts/pointers/ideas will be appreciated, before I have to raid the wifes piggy bank = my bank account

P.S. I don't have access to a code reader. Will buy one, if someone can recommend one for use by an amateur but capable spanner operator.

[minesapasty]

Update:

Having had an idea, I did a search on You Tube and found a couple of things to watch. I then rushed out to see if the tips worked...... only to find that the fault didn't show up..... there's nothing worse than an intermittent electrical fault..... anyway, I wandered around the car putting a finger lightly on each of the sensors, and yes, I could definitely feel something on each of them..... so if anyone needs to know how to check which sensor is faulty, that is what you do, and to answer my original question, one faulty sensor will trigger a fault saying system failure, not just a sensor failure..... hope that this helps.

I'm now planning on finding out what is causing my intermittent fault