C4 Parking System Fault

[gosnoid72]

When I start the car, without the parking assist system disabled, I get a fault message on the dash 'Parking Assist System Fault' or something similar. Last night I disconnected all eight sensors, thinking that by removing a faulty sensor, it would remove the fault. It didn't make any difference, so I'm wondering if a disconnected sensor is actually a system fault? If so, can I short out each plug to make the system think that the sensor is fitted? I've read the other posts about feeling the 'buzzing' sensors, if they're working and I'll try that (does that still apply if the system is in fault?). I assume that the system is split and the rear sensors are only live in reverse and vice versa for the front ones?

[GiveMeABreak]

That isn't going to help! The parking assistance ECU does a self-check each time the vehicle is started. By disconnecting the sensors you have basically created more faults.

Try my touch test as you have referred to, but otherwise you need a decent diagnostic system like Lexia / Diagbox to determine which part of the system or which sensor is faulty.

Shorting them out is only going to destroy them.... but won't make the warning go away.

If you don't want the system working then it will need disabling with the diagnostic tools I mentioned above.

[gosnoid72]

Cheers Marc, I thought as much. I'll try the vibration test at the weekend.

[gosnoid72]

Lexia scan complete. Faulty sensor identified and changed. Parking system fixed!

[GiveMeABreak]

Great, thanks for the update.

When my C5 started playing up I changed one sensor, then a couple of weeks later the parking system fault message reappeared - but diagnostics confirmed a different sensor - changed and no problems. A month later it happened again - another sensor on a different location! So be aware that if you get this happening to you it may just be the end of service life of some of the sensors - so that's why it's important to check positions.

[gosnoid72]

I shall bear that in mind and glow in my small victory for a while! Thanks.

[Colinf73]

OK guys I had this problem on my wife's 2018 c4gp and managed to fix it as follows.....
Same fault on start up "Park assistance fault" flashes up.

I can confirm that this model needs to be started in order to activate the parking sensors. It cannot be done just by powering the ignition and selecting reverse.
Even although the fault is there the system will still send power to the sensors when reverse selected but will not give any indications on the display.
So with my wife sat in the driver seat I got her to start up and select reverse.
This allowed me to do the "tick test" at all sensors.
Only one was not ticking (rear middle right).
I swapped it with the middle left and the fault stayed with the original position.
I then knew that the fault was not a sensor but wiring to that position.
Easy con checks first.....
Looking at the wiring manual all pin 1's are linked to each other so I took the connector off the aft left corner sensor and con checked between both pin 1s......all good.
All pin 3s are also linked to each other and a similar check was done.... all good.
The tricky one to check is pin 2 on each sensor connector as each is a separate wire back to the control unit.
You could remove the connector at the control unit and identify the wire colour for the pin 2 you are looking at and con check from the unit connector to the sensor connector.
In my case it was a white wire going to this sensor pin 2.
I was lucky though....tracing the loom back on the underside of the car I noticed the loom wrapping was scuffed and just under the hole was ......yep the white wire covered in verdigris!
When I pulled gently on this the wire broke in half! (See pic one)

I then crimped in a section of spare wire I had (pic 2) and that was that. Job done.
Started up and fault gone.
Hope this info may help with future diagnosis of the same problem (don't dive in and change a sensor if one is not ticking, swap it with a known good one).

[dinomerlin]

I'm sorry for posting here because I couldn't find an answer. Does it have to be the same BOSCH number if it matches the PSA on the blind spot sensor for it to work properly. Mine is broken, the number is PSA 9665468077; BOSCH 0263013236. On ebay I found a used PSA 9665468077WP; BOSCH 0263013131. thanks

[GiveMeABreak]

You must have exactly the correct part number as the sensors can differ (especially blind spot sensors, which are usually different part numbers to the other standard parking sensors). The main part number would seem to be correct minus the 'WP' at the end, but as far as the main part number is concerned that should be fine.

[dinomerlin]

You must have exactly the correct part number as the sensors can differ (especially blind spot sensors, which are usually different part numbers to the other standard parking sensors). The main part number would seem to be correct minus the 'WP' at the end, but as far as the main part number is concerned that should be fine.

Thanks, but I'm not sure what the BOSCH number is. If the main PSA is adequate, perhaps the letters WP are not so essential for the correct operation of the sensor.