C5 Tail Lights

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Re: C5 Tail Lights

Post by GiveMeABreak »

sparksie wrote: 20 Dec 2018, 00:27
sparksie wrote: 20 Dec 2018, 00:11 ...That's 3 of them in a very short time.


Or put another way, a 100% failure rate for all of this model I've ever had any dealings with!
How can such a failure mode even be possible, let alone at that frequency?
Surely, if the lighting circuit is going to be split, common sense dictates that it should be split side:side, not front:rear.
That way, should one circuit fail, there will be a noticeable drop in light output, from the driver's perspective.
The present setup is so dangerous.
Even my 1985 Volvo 7 series has a very obvious bulb failure indicator, so how is it acceptable, over 20 years later, for a high end car to be totally unlit at the rear without any way for the driver to know?
I'm not aware of any particular lighting issues and there isn't any TSBs for the lights.

The only bulb warning systems are as follows (note - for any indicator bulb that is out, the flashing speed is doubled). But as you can see there is no warning for the rear tail lamps....
Lights ConcernedMessage Displayed
Main BeamsMain Beam Headlamps Bulb Faulty
Dipped BeamsDipped Beam Headlamps Bulb Faulty
Fog LampsFog Lamps Bulb Faulty
Reversing Lamps (Left Hand )Reversing Lamps Bulb Faulty
Reversing Lamps (Right Hand )Reversing Lamps Bulb Faulty
Rear Stop Lights (Left Hand )Brake Lights Bulb Faulty
Rear Stop Lights (Right Hand )Main Beam Headlamps Bulb Faulty
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Re: C5 Tail Lights

Post by sparksie »

bobins wrote: 20 Dec 2018, 20:39 It's a good job we still have an annual MOT test over here to pick up such things as non-working rear lights. To think there were moves to make it a 2 yearly check :shock:

Hi bobins
Yes, we also have annual testing and, as I said, the latest two were only over here on holiday from the UK, where they presumably went through the MOT.
I'm so lucky not to be sporting a French bonnet mascot!
I certainly gave my non-ABS brakes a workout and my better half can vouch for the inertia reel seat belts effectiveness.
If this is what we can expect from CAN, I think I'll stick to my elderly scrappy-dodgers.
That way I can, at least, guarantee my fellow road users they'll be able to see me when they're driving into me.
I think I can make a design improvement that will guarantee tail light illumination when ANY front lighting is active, without upsetting the ecu.
Obviously, I'd have to own any car I was experimenting on, so it may be a while before I get to do that, but I won't be driving one in the dark without checking the tail, unless such a mod has been carried out!
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Re: C5 Tail Lights

Post by GiveMeABreak »

That might be more of a challenge than you realise, given that there is a whole heap of control mechanisms involved for the lighting systems, each controlled by a series of conditions and ECUs, as these are variable involving the control module inside the steering wheel, the BSI and the engine fuse box or a combo of these depending on lighting conditions and other calculated factors, plus back up mode logic. And then there is the controller CAN networks to be wary of in that these can affect other systems if interfered with. 💣
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Re: C5 Tail Lights

Post by sparksie »

No, not especially difficult.
A dummy load (just a resistor) in place of the bulbs, leaving the existing BSI control hash blissfully unaware of any change.
Once that's happy, you can then do whatever you like to power the bulbs.
When I was typing that yesterday, I was thinking of a rudimentary OR gate, with a power transistor and a reed relay on a small circuit board. This would monitor all front lights and if any of them was lit, supply power out which could be used to light the rear bulbs.
However, on reflection, I realised I was over thinking it and there's a much simpler way, using off-the-shelf parts.
In these modern times, daytime running lights are the norm, so if the engine is running, the lights should be illuminated.
So, an ignition controlled supply, feeding a voltage sensing relay (vsr), via a fuse, would achieve this.cheaply and easily.
Ignition on and voltage exceeds 13.5V trips the vsr and the lights come on. Simple and reasonably elegant and doesn't upset the BSI in the least.
For added reliability, use a separate vsr for each side.
Of course, this system would douse the lights if the alternator fails, but at least the driver would know there was a problem.
Caveat: I have not done this and if anybody wants to take the idea and run with it, they do so at their own risk!!!
However, I design analogue systems such as this in my daily job. I'm also comfortable with rudimentary logic circuits and have designed traffic light controllers for experiments/exams, so I'm pretty happy that I can build a workable, safe and reliable system that will be better than the beta system installed as standard.
I'm now wondering, if QC didn't pick up on this design flaw, what else might they have missed?
Could ghosts in the CAN be the C5's equivalent of the Xantia strut tops?
Scary!
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Re: C5 Tail Lights

Post by GiveMeABreak »

I believe the rear tail lights have separate circuits as 2 are in the tailgate and 2 are on the body rear wing clusters and I know these have different wiring. I will be following with interest!
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Re: C5 Tail Lights

Post by admiral51 »

It only takes 60 seconds to do a walk round and check the lights are working and it is easy to check the brake lights are working in the dark, no need for anyone to assist, just a little common sense.
As for the indicator bulbs i have found that if you put the hazards on it does not show a bulb out, left and right on the stalk will show a bulb out by the quicker flashing.

Side note i have seen lots of cars with no rear lights but front lights on during the daytime, maybe a DRL issue, i think the old saying is see and be seen :)
Just because it has an MOT does not mean it is roadworthy the day after, maybe people are already in the lax habit of not checking a vehicle is roadworthy before they drive it.
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Re: C5 Tail Lights

Post by sparksie »

Ahem
Very few people indeed are going to stop on the motorway hard shoulder, in heavy rain, climb out and walk around their car, simply because it has got dark enough to require lighting during their journey. Any that do have much bigger problems than a lack of rear illumination!
Admittedly, that is an extreme example, but seriously, in 2018, does anybody really do pre-flight checks before nipping to the shops?
Most modern motorists don't know how to open the bonnet.
Responsible ones check their tyres once or twice a month and routinely run an eye over the dash to check for any bulb failure warnings, or other fault indications.
This particular fault condition, being a design flaw, doesn't give any indication. The bulbs are intact, but the BSI has decided not to light them, despite being requested to. IMHO, it should not have this option.
I'll have access to the 2008 one again next week, during the holiday.
I still need to get to the bottom of a wiper problem with it, so I can have a play with the lights and see can I provoke the problem.
I noticed there is a setting called "automatic" on the headlight switch, last time I was in it. What is the purpose of this and how should it be used, does anyone know?
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Re: C5 Tail Lights

Post by myglaren »

sparksie wrote: 23 Dec 2018, 03:27 I noticed there is a setting called "automatic" on the headlight switch, last time I was in it. What is the purpose of this and how should it be used, does anyone know?


On auto, the lights come on at dusk - equates approximately to when street lights come on. Also they will come on after a few sweeps of the wipers - which will also close any open windows.
Wipers have an auto setting too.
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Re: C5 Tail Lights

Post by Paul-R »

sparksie wrote: 23 Dec 2018, 03:27I'll have access to the 2008 one again next week, during the holiday.
That will be an X7 then surely?
myglaren wrote: 23 Dec 2018, 03:34 - which will also close any open windows.
Wasn't that useful function removed on the X7?
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Re: C5 Tail Lights

Post by GiveMeABreak »

Yes, correct Paul, the automatic window closing when raining function has been dropped quite early on. I suspect it was due to safety issues in that the windows would raise when wipers were on more than intermittent speed. The window motors (despite those models fitted with anti-pinch) were still powerful enough to seriously damage the fingers of a child or cause a lot of damage to children / frail adults or animals if caught when closing. The speed at which the windows closed was significant to have a 'chopping effect'. I remember trying it on my MK I C5 with a small branch and I was quite surprised at the force it exerted.

Going back to what Sparksie said. that was what I was trying to convey about the BSI and the electronics involved on these modern cars. The lighting system has a lot of 'and', 'or' 'if' logic to determine what and when lighting comes on and for how long and under what circumstances. Of course manual switching on of the lighting always takes preference over the automatic functions. However the digital Body CAN and Comfort CAN and LIN data networks also play a significant role in the sending of communications between all the components.

These are the functions managed by the exterior and signalling lighting on an X7 and also the systems equipment used in their operation:
  • Automatic switching on of the dipped headlamps by means of exterior brightness management (Rain and brightness sensor )
  • Flash of headlamps
  • Directional headlamps (dynamic cornering lighting and automatic beam height correction) or manual beam height correction
  • Manual follow me home lighting (Switching on of the lights on unlocking)
  • Automatic guide-me-home lighting (Follow me home)
  • Remote switching on of the lights
  • Remote location of the vehicle
  • Management of the daylight lamps
  • Automatic lighting of hazard warning light on high deceleration
  • Management of the priority of the direction indicator lamps
  • Switching on of the lights for the trailer
  • Number plate lighting
  • Detection of faulty bulbs
  • Management of the lights-on warning buzzer
  • Instrument panel - Central instrument panel display.
  • Hazard warning light indicator.
  • RT4 audio/telephone.
  • Manual headlamp beam adjustment.
  • Switch module at the steering wheel (Lighting switch part).
  • Steering wheel with fixed central controls.
  • Rain and brightness sensor .
  • Trailer relay unit.
  • Built-in systems interface .
  • Connection board - fuse box(Engine compartment).
Example Flow Chart (for Halogen System only) Dipped / Main Beam
X7  Halogen Dipped Beam Flow.PNG
Faulty Bulb Reporting:
When a bulb is faulty, the display of the message of type "headlamp bulb faulty" is forwarded to the user via the instrument panel display.
The warning lamp corresponding to the faulty lights comes on for 19 seconds, accompanied by a brief sound when the fault occurs.
Lights ConcernedMessage Displayed
Main BeamsMain Beam Headlamps Bulb Faulty
Dipped BeamsDipped Beam Headlamps Bulb Faulty
Fog LampsFog Lamps Bulb Faulty
Reversing Lamps (Left Hand )Reversing Lamps Bulb Faulty
Reversing Lamps (Right Hand )Reversing Lamps Bulb Faulty
Rear Stop Lights (Left Hand )Brake Lights Bulb Faulty
Rear Stop Lights (Right Hand )Main Beam Headlamps Bulb Faulty
As you can see nothing for the tail lamps - and considering there are 4 of them on the X7 at the rear, that's quite an oversight.
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Re: C5 Tail Lights

Post by myglaren »

Surely the 'anti-pinch' would preclude the excision of digits? May try it one day - or not, lost too many already :(

My son had an interesting experience with it - he had come off his motorbike and broken some bones, including his leg.

He had to go to the hospital a couple of times a week for follow-up procedures, he went in my C5.
Leaving the hospital one day, he tried to put his ticket in the reader but each time he opened the window, the rain sensor closed it again. In the end he had to get out of the car, not rasy with a broken leg and only a few inches clearance for the door. The queue behind him wasn't particularly amused, not knowing the problem.
Shame he didn't realise that turning the wipers or engine off would defeat the window closer.
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Re: C5 Tail Lights

Post by GiveMeABreak »

It would seem that the auto closing function for all windows was deactivated if a window command button was pressed whilst the wipers are working - so that switched it off according to this:
  • The vehicle windows close when the wipers have been operating in continuous slow or fast speed for at least 5 seconds, except when the washers are operating.
  • The command of a front window deactivates the closing function for the 4 windows, if the window command is made when the wipers are operating.
  • The automatic closing function is deactivated until the next time ignition is switched off.
All I know it that is was still quite a powerful closing force. I also miss the remote opening of the windows from the MK I, which again was dropped on the C5 MK 2 on - and only the closing of the windows and sunroof are maintained using the fob on the MK II & III :(
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Re: C5 Tail Lights

Post by sparksie »

Just a quick update.
I was down in the devil car today and, while waiting for the laptop to boot up, I had a play with the lights.
The headlights always come on with the ignition, unless the switch is in sidelights position.
If the switch is either OFF or AUTO, the tail lights and number plate lights don't illuminate, but high/low beam work as requested.
If the switch is in either SIDE or HEAD, the lights appear to work correctly, with 4 tail lights and the number plate lights all in action.
I forgot to check the rear fog lights, but assuming the British cars were like this one, it seems the fogs will work regardless of headlight switch position.
There appears to be no way to have ignition on without headlights, so my diagnostic session had to be kept short, to preserve the battery.
This seems as though it must be a fault, given these cars' well documented voltage issues. Starting, especially on a cold day, with headlights blazing is a sure way to bring the battery voltage down.
Given the fact that I'm able to make the lights operate legally, I think I'll retrain the owner, rather than try to fix it.
This car is accumulating problems faster than I can hope to remedy them.
Pretty important for other owners, too, I think.
Just because the headlights are on and you can toggle between high and low beam, does NOT mean you're correctly lit. Make sure the lights are actually switched on, or if possible, check the back of the car.
Unless something changes, I'm considering this issue solved by workaround, though not truly fixed.
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Re: C5 Tail Lights

Post by GiveMeABreak »

Not correct on the fogs, Sparksie.

The fogs only work directly in relation to the headlamps being on - so will ONLY work when the dipped or main beam light are on, by turning the lighting barrel forward once to activate front fogs, and a second roll forward to activate the rears too. then reverse roll to deactivate rears and a second roll rearwards to deactivate fronts. In either case, fogs automatically switch off with the extinguishing of the headlamps. The fogs also do not work with sidelights only on.

You don't say what you have done, but the headlights on '0' or off should not operate at all and on 'AUTO' only according to whether it is raining or in dim lighting.
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Re: C5 Tail Lights

Post by sparksie »

Hi Marc
I don't say what I have done simply because, so far, I've done nothing.
I've observed 3 different cars illegally lit and played with different switch positions on the one I have access to, in order to establish the true extent of the problem.
As found, with everything entirely original, the symptoms are as I indicated.
Yes, following my visit today, I can confirm you're correct, the fog lights on this one don't work in SIDE, but they do in OFF, AUTO and HEAD. I repeat, the only way to extinguish the headlights is to turn the ignition off.
There are no faults in the BSI relating to lighting.
This not being my car, and given the extraordinary rate at which faults are developing with no interference from me, I'm very reluctant to touch it at all, let alone deviate from the standard.
If I ever find myself in the unfortunate position of owning one of these, I'll cheerfully chop out all nonsensical computerised gimmicks at the first sign of trouble and design my own loom for required functions, secure in the knowledge that, if it all goes wrong, it can be weighed in and all I'll have lost is some free time.
With this one, my fingers have been badly burned and my charitable streak has been virtually erased.
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