C5 BHI investigation query

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MaxyBoy2000
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C5 BHI investigation query

Post by MaxyBoy2000 »

Hi All,

I have a 2002 Citroen C5, which is my favourite car of all time.

I've seen people talking about the BHI ( Built-in Hydroelectronic Interface ) which is just a wonderful bit
of technology.

I'd like to do some investigation, treating the BHI as a black box, I want to put an oscilloscope on the control
inputs to this device to see what PWM signals, or whatever, are used to make the front suspension go up or down.

I'm not interested in the general complexity of the suspension system, with all that gets monitored electronically.
Just, what it takes to make the BHI valves cause the front of the car to rise, and then fall.
I propose parking my C5 on level ground and turn the steering wheel to make the wheels at an angle.
A fault with my C5 causes the front to 'cycle' up and down, even when the key is out of the ignition.
Then I intend to connect the input of the BHI to an oscilloscope and note down the recordings.

What does anyone think here? Any suggestions would be greatly appreciated.

I'm not trying to fix this, as it's a minor irritation really and I find it quite amusing.

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GiveMeABreak
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Re: C5 BHI investigation query

Post by GiveMeABreak »

The 'hunting' or 'nodding' is a well-known issue - more so on early C5s.

Depending on the version of BHI you have, it may or may not be able to get a software update. The only way to tell is to get to a dealer and they will be able to determine if yours is upgradable or not. An upgrade to the BHI software should cure this, otherwise if the BHI is a non-upgradable version, the official solution was to replace the complete BHI. So my advice is always try to park with the wheels dead ahead to reduce the frequency of it.

As for the system overall - you can't really ignore some parts of the system to properly understand it. Very basically - the system relies on various sensors to determine ride mode / adaptation and height correction. There are several versions of the system depending on whether you have Hydractive 3 or Hydractive 3+.

Components such as the engine ECU, the ABS / ESP ECU, Steering Wheel Angle Sensor, Front & Rear Height Correctors all get input into the suspension ECU incorporated into the BHI, which makes height corrections as required or changes the ride from comfort to sport mode as required by the driving and road conditions (depending on the system you have).

The input and exhaust valves are controlled by the electrovalves as required, but the actual pump is only operated occasionally to maintain the required pressure and does not run all the time.

wheeler
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Re: C5 BHI investigation query

Post by wheeler »

There is a official wiring modification you can do to the MK1 C5 that cuts the power to the BHI after a few minutes that stops the suspension nodding when parked.

MaxyBoy2000
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Re: C5 BHI investigation query

Post by MaxyBoy2000 »

Thanks Marc & wheeler.

Does anyone know why my MK1 C5 ( Non sport ) reverts to 'nodding' when parked with the front wheels at an angle,
( i.e. not straight ahead ) ?

I understand it's a fault, but what's is the car trying to do ? Self level ?

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GiveMeABreak
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Re: C5 BHI investigation query

Post by GiveMeABreak »

It was a calibration issue which the software update corrected according to the Technical Service Bulletin at the time IIRC - which as I said on some units could be applied to fix the issue.

wheeler
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Re: C5 BHI investigation query

Post by wheeler »

From build date 13/10/03 the BHI unit had modified software that was meant to stop this however it was not always successful. The BHI can be updated with Lexia to the later version however again its not always successful in curing the issue. Citroen released a wiring modification to fit a relay that cuts the power to the BHI after a few minutes so that worst case it will only do it for a couple of minutes then stop so that it wont flatten the battery.
If you are interested in doing the mod i can look out the parts list & instructions. You will need to be confident in splicing into wires in the BSI & crimping relay terminals.

MaxyBoy2000
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Re: C5 BHI investigation query

Post by MaxyBoy2000 »

Thanks Wheeler.

I would like to see those instructions if they are easy to hand for you.

Regards,

Max

MaxyBoy2000
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Re: C5 BHI investigation query

Post by MaxyBoy2000 »

Does anyone know if the BHI receives CAN BUS data into it's Electronic Control Unit ?

Thanks.

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GiveMeABreak
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Re: C5 BHI investigation query

Post by GiveMeABreak »

Yes the BHI has direct CAN Bus connections to the BSI - from where there are CAN connections to the rest of the vehicle's systems.

wheeler
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Re: C5 BHI investigation query

Post by wheeler »

MaxyBoy2000 wrote:
09 Apr 2021, 11:20
Thanks Wheeler.

I would like to see those instructions if they are easy to hand for you.

Regards,

Max
I dig them out over the weekend at some point & will need to scan them first.

If you have Lexia check the software version, if its below version 000000730 the software update will not work anyway and this is the when BHI would need replaced to even attempt the update. This workaround was released to remove the need to replace the BHI.

wheeler
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Re: C5 BHI investigation query

Post by wheeler »

It was easier just to take pictures.
In the wiring diagram at the end the relay with the dotted line around it is the one you are adding.
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MaxyBoy2000
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Re: C5 BHI investigation query

Post by MaxyBoy2000 »

Brilliant Wheeler.

Thanks for going to all that trouble. I appreciate it.

Thanks Marc for your Can bus answer.

wheeler
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Re: C5 BHI investigation query

Post by wheeler »

The CAN lines can be seen at the bottom of the diagram, they are the 2 thicker pairs of wires shown on each side of the BHI in the diagram.