C4 VTS with parking assist system fault

[mtank]

Hello!

I have a 2005 Citroen C4 VTS with front and rear parking sensors, which aren't working. When I turn the reverse rear I get the error "parking assist system fault". I bought the car recently with the error already, thinking that would be something simple to solve, but after some attempts to fix it, I changed my mind.
What I have checked so far:
- Touch test on the sensors (none is working)
- Diagbox, the first time I got the below error related to parking:
> BBDB | Sensors supply fault | Short circuit to negative
- Fuses (checked all of the ones suggested here in the forum)
- Parking ECU (I replaced it with another one (exactly the same) and after that, I checked again with Diagbox and got more 2 errors related to the parking system besides the BBDB)
> Interior rear right sensor fault
> Exterior rear right sensor fault
- Removed the front bumper and seems that the parking cables are ok, except for a loose cable (see attached image).
- Earth wire I tried to check, but I have no idea where this is.

VIN: VF7**************[VIN obfuscated, can be read by forum staff]

I appreciate any help, thanks!

[Hell Razor5543]

Hi, and to the Forum.

A simple test might be to swap a suspect sensor with a known working one (so, for example, swap the exterior rear right sensor with the exterior rear left sensor) and then run another Lexia check. Sensors can fail, and if the fault follows the sensor it proves the sensor is faulty.

[mtank]

Hi, thanks, this forum is awesome btw ;D
So even with this BBDB error (sensor supply fault) now it could just be a matter of replacing a sensor? Or could it be an error still related to the old ECU? Maybe I have to clean the errors and check again xD
I'll try it next Monday and let you know.

[Hell Razor5543]

Your pictures show 2 sensors are at fault (which implies the remaining sensors are in working order). Doing a sensor swap is (depending how difficult it is to remove them) is a very simple test. Yes, you have other issues, but a swap test can be effective at nailing down whether a sensor is faulty, or something else. If you swap two sensors over, and the fault follows the suspect sensor, that proves the sensor is faulty. Conversely, if the fault stays in the same location that would suggest the suspect sensor is in good working order, but the wiring (or ECU) is at fault instead.

It would be a good idea to note down all of the faults (as you have with your photos), make a simple change (such as swapping two sensors), clear all errors and try again. Then compare the new error report against the old one. Good practise is to deal with one fault at a time, using simple steps.

The advantage to using the good sensors on your C4 is that it is a 'free' test, as you are not having to buy extra sensors to test your parking system. It is likely (but NOT definite) that all of the rear sensors are of the same type.

[mtank]

Got it, it makes sense. Thanks ;D

[mtank]

So, I only had time today, but good news. I ended up ordering the rear sensors and changed them. It worked! No more errors. I still need to check if the BBDB error persists on diagbox, but on the car display it’s free of any errors. Also, I haven’t figured out the loose cable, but it seems to be an adapted installation for something that was removed, maybe a DRL?
Well, that’s it, thank you!

[Hell Razor5543]

If, by loose cable, you mean a cable with nothing connected to it, it may be possible that the wiring loom has connections for optional extras that were not selected for your vehicle when she was built.

[mtank]

Yes, that’s what I meant. It makes sense, the VTS also comes with the road assistance as optional, it could be that.
So, the BBDB error is also gone, the parking assistance is now fully functional. Thanks James!