All of a sudden, whenever we put our 2006 XJ8L VDP in reverse, the rear parking sensor blares a steady tone - like we're 1 foot from something. I can silence it by hitting the overide P button on the overhead console.
Any ideas where to start?
Module, disconnect sensor wires one at a time (how?), etc. ??
BTW - the front sensors work fine.
Any help would be appreciated. Thx.

 

Hi 200Volts,

We have the same issue on our '04, and if I recall correctly, reports by others on the forum indicate this is due to a failed rear park assist sensor or a problem with its electrical connector or harness (for example, chafed insulation allowing a wire to short to ground). I've had other more pressing repairs to attend to so I haven't gotten far enough to tell if you can access the electrical connectors without removing the rear bumper cover, but I'm sure other members will be able to tell us.

One simple test you can conduct yourself is this:

Set the park brake or chock the wheels. Turn the key to Position II but do not start the engine. Put the gear shift lever in Reverse. Now go to the back of the car and put your ear close to each sensor (the round circles in the bumper cover). You should hear a faint clicking sound. The sensor that doesn't click is the one with the problem.

I'll look forward to hearing from our knowledgeable members who have resolved this problem.

Cheers,

Don

 

There is a TSB regarding faulty front sensors, but it talks about both front and rear sensors and the system:

"DIAGNOSTICS
When the ignition is turned to position II, the system carries out a self-check. If a fault is
detected the control module will generate a fault code, a continuous warning tone will
be emitted for 3.5 seconds and the system will be deactivated. Therefore unless a fault
code is generated and the 3.5 sec warning heard, it should be assumed that the system
is operating correctly.

SPURIOUS WARNINGS
There are some conditions that will activate the system when there is no obvious
obstruction. If the vehicle is moving on loose gravel, which has a totally random surface,
the sensor could receive a return signal and operate the warning. It is known that
anything that emits sound waves at a frequency between 15-150 kHz may affect the
sensors. Known influences include fire engine klaxons, pneumatic tools, air brakes, high
performance motorcycle/auto engine exhausts. Any of these can cause the warning
sounder to be activated. In harsh weather conditions, such as very heavy rainfall, the
volume of water passing over the sensor can cause it to operate.
This will also happen if the sensor is covered by ice, frost or grime buildup. In none of
these circumstances is there anything wrong with the system."


From your description, it sounds like you are getting the warning/fault tone and it should be recording a DTC that can be read with IDS/SDD software.

The first thing I would do before anything else is to clean each sensor lens to be sure it isn't reflecting the signal back to the sensor due to dirt or grime.

 

I ran into the same issue a while back. I cleaned the backup sensors with windshield cleaner and that did the trick. Apparently they are real sensitive. My car had some salt from winter driving that affected the sensors.

 

I had the same problem when my battery went flat and had to get a jump start also the reverse lights where on whilst still in park then after that the reverse beeper would go off when put in reverse so checked all sensors all where making a clicking sound . Car was dirty so gave it a good wash a few days later the beeping stopped and the reverse sensors have worked properly ever since ( touch wood)

 

The Park Assist system alerts you to a sensor failure by sounding the beeper continuously for eight or more seconds when you put the car in reverse. Once you are up to speed, the noise will stop, until you slow down for an intersection, etc., and then it starts to blare again. You can manually turn it off with the button on the overhead consol, but it reactivates everytime you put the car the reverse. You can check to see if one or more of the eight sensors (four on each of the front and back bumpers) are out of commission by turning the ignition to position two (power on but engine off), manually engaging the hand brake lever, and then putting the gear shift selector to Reverse. With the car in this condition put your ear up to each sensor and your proximity to the sensor will cause it to make a faint rapid clicking noise. If it doesn't you have a problem with that particular sensor. Before you go to all the labour of removing the front or back bumper to replace the bad sensor, try an old WD 40 trick. Liberally spray each sensor with copious amounts of WD 40. Wipe off the excess and let the sensors dry for an hour, then turn your car on. I'm on my third Vanden Plas (I have kept the '08 as they stopped making them in early '09) and I've had your annoying problem on each car. Each time it has happened I've used the WD 40 trick and the problem went away for a year or more. Common causes are water getting into the sensor housing after driving in rain, or having your car buried in snow during a blizzard, and my favourite - having the car detailed. Car wax in particular will trigger the problem. In these cases the 4D 40 drives out the moisture or wax and problem solved. It may not work for you - but WD 40 certainly won't hurt anything and if it works for you then you've saved yourself time and money.