C5 x7 rear parking sensors not working but computer says yes

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petef
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C5 x7 rear parking sensors not working but computer says yes

Unread post by petef »

The rear parking sensors on my 2009 C5 x7 Tourer have stopped working. The sat nav screen display still comes up when reverse is engaged with the customary beep, but as you reverse no warnings are given either on the display or audibly as you approach something. Connecting to Lexia shows no fault whatsovever - communication with Bosch parking ECU established and no fault found. Doing the parameter tests I can switch the sensors on and off via the Lexia; when on it declares the system 'active' But it just doesn't work.
Only clue is that yesterday when starting the car and engaging reverse there was immediate audible and visual warning and it showed close proximity of something behind when there was nothing there. Maybe one of the sensors has gone on the blink - but normally this just shuts the system down and shows fault on Lexia. Any ideas?

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GiveMeABreak
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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by GiveMeABreak »

If there is a fault, yes, the system usually stops working. Having said that, depending on the fault, the system can come on and off - indicative of a temporary fault.

First thing I suggest is having a look at the parking assistance ECU. It's in the boot area - should be on the rear right hand side - I've arrowed in red:
Parking ECU.PNG
Check to make sure none of the connectors are loose, but more importantly that no liquid has spilled onto / into the unit. Containers of screenwash or water are notorious for leaking and the liquid draining out below and onto these units.

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petef
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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by petef »

Thanks for the quick reply Marc. Forgot to say that I had checked the ECU . It's on the side of the spare wheel well on the Tourer and was bone dry. Connectors not loose. Just put a chair 1 foot way from the rear of the car and engaged reverse. Momentarily sensed it on display and audibly, but then stopped working whilst still displaying the car outline on screen. I fear the ECU may be on the blink even though Lexia says it's ok. This is wierd

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GiveMeABreak
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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by GiveMeABreak »

Ok, so try the finger test - as it were...

Ignition on, stick in reverse, then use your finger to very lightly almost touch the surface of the sensor - you should feel a tingling sensation / slight pulsing. That will tell you that the sensor is working. Normally, when one of these is not working, the ECU disables the system until it gets feedback from all the sensors. But if you are not getting any errors, it may well be the ECU itself as you suggested Pete.

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petef
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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by petef »

So, tried the finger test, definitely no tingling.....! Mind you tried it on the front sensors, which are a Citroen - Valeo branded - accessory activated by a switch on the steering column. No tingling there either - even though they work fine and were beeping away. So I have ordered a second hand but guaranteed ECU, we will see what happens. Does the change of ECU have 'notified' through Lexia, Marc, or can I just swap them?

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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by GiveMeABreak »

Ok so here's the thing...

Your VIN indicates no front sensors only a rear set - so is this an aftermarket add-on for the front? If so, I assume it has it's own system and independent of the car's other systems.

The parking assistance ECUs are option-specific on the X7. The unit will depend on Saloon / Tourer firstly, and will then be one of 2 options; an ECU for Rear Sensors only, with or without the later video option, and the second option of ECU for the Tourer is for front and rear assistance with or without video.

So make sure any replacement is the same as the ECU part number you are replacing Pete. :)

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petef
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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by petef »

Thanks Marc. Yes the front sensors were a dealer add on.The second hand ECU I found on ebay was only £14 so worth a punt. It is exactly the same part number as the one in my car. Seems like the same part was fitted to a variety of other Citroens including the C4.
Is it plug and play or is Lexia authorisation required?
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C5 parking sensor.jpg

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GiveMeABreak
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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by GiveMeABreak »

Configuration of the ECU only has a few parameters: Saloon / Tourer, Transmission Type: Auto / Manual or Piloted, Front Parking Assistance - configure 'Absent' in your case and then Presence of Measurement of Available Space Function - which should also be configured to 'Absent' in your case.

You may not have all those options listed anyway - but now you know what they should be.

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petef
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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by petef »

So new ECU fitted but system still not working.
To recap : Lexia says no fault found, as before.
New ECU was configured for Estate and Auto - the only two options.
Actuator test says sensors are working correctly
But display on screen shows only car silhouette with usual 'boing' when reverse engaged, no visual or audio display warnings on screen when reversing and approaching objects.
Also tried a known duff sensor - one I had previously replaced. Sure enough the parking assistance is shut down on display straight away, indicating ECU knows something is wrong.
I'm completely stumped....

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GiveMeABreak
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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by GiveMeABreak »

Ok, so I'm having a look at this, but you'll have to forgive me if I ask this.... but are you 100% sure that the parking assistance disable button has not been activated on the dash accidentally?
Parking.PNG
Parking.PNG (77.28 KiB) Viewed 69 times
Secondly, when replacing the ECU, did you follow the BSI Reset / Battery Disconnect / Reconnect Procedure? This is specifically mentioned when replacing it.

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petef
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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by petef »

I'll just about forgive you. Yes I'm 110% sure the disable button was not activated - except when I was checking that it worked in parameters on Lexia. If it was turned off nothing would show or be heard when reverse is engaged anyway. I haven't done a BSI reset, doesn't seem necessary, - new ECU was recognised fine and configured and settings saved on Lexia.

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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by Hell Razor5543 »

I would ALWAYS do a BSi reset when making any major electronic changes to a C Series Citroen. There is an awful lot of electronics in there, and doing the BSi reset will allow all of the ECUs to shut down properly, and then to do a clean start up cycle. Just turning off the ignition and removing the key puts the ECUs into a 'standby' state (and when a computer system is in standby any glitches that have occurred may be retained next time the ECUs start up. Yes, it takes time, but it will eliminate any glitches (REAL problems will remain, however, if there are any).

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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by GiveMeABreak »

petef wrote:
27 Jun 2020, 17:53
I'll just about forgive you. Yes I'm 110% sure the disable button was not activated - except when I was checking that it worked in parameters on Lexia. If it was turned off nothing would show or be heard when reverse is engaged anyway. I haven't done a BSI reset, doesn't seem necessary, - new ECU was recognised fine and configured and settings saved on Lexia.
:rofl2: Well I had to ask, as it's one of the official checks under fault finding!

So next - have you had anything changed instrument panel or dashboard wise? If not, then there is another possibility apart from electrical / multiplexing:

It is known to some of us that some of the clone interfaces can play havoc with the parking assistance ECU - in that once it has been interrogated by the VCI, it can leave the parking assistance ECU in an unconfigured state. So connect up Diagbox again, then run the Global test, then access the parking ECU, go to manual configuration, then change the vehicle from Estate / Tourer to Saloon, apply the configuration, then go back into the parameter and change it back to Estate.

Come out of the system, close everything down - do not activate the revering sensors yet! shut everything down, lock the car and leave it for 10 minutes for the BSI to close all the networks and put them to sleep.

Then see if that has resolved it.


It's another reason why the BSI Reset is there because it shuts down the ECUs properly and wakes them up correctly - and again, is part of t he official procedure when replacing the PA ECU.

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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by furriegurrie »

Did you by any chance use a 13 to 7 pin converter and leave it in the electrical socket? This often will deactivate the rear sensors.

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petef
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Re: C5 x7 rear parking sensors not working but computer says yes

Unread post by petef »

So I left the car to it's own devices yesterday. Didn't touch it or even go near it. Just glowered at it from a distance. Obviously piqued it a bit because today the sensors are working again. With the the original ECU and no BSI reset or reconfiguration or anything. A long sleep seems to have been the cure.....?