C5 cruise control limiting

[Richard Stevens]

Really been enjoying using the cruise control, for better economy, smoothness and that general relaxation so good on long journeys.
On my last trip, however, I found that on the steeper climbs (French motorways, so not desperate stuff!) the selected speed gradually drops off. Application of the right foot gives me the power, so there is more in there.
Oil and water temps are fine, and idle is also. No other signs or symptoms; it seems the control is not giving sufficient 'authorisation' for more power.

I haven't seen a thread on this before though I would not be surprised if there is one in here somewhere.

Haven't been to anywhere commercial for advice yet, thought this is the best place to start.... anyone got some ideas?

RichS

[rmunns]

Haven't learnt yet how to use Cruise, but did engage the limiter and found it spooky that there is no more power when you reach the set speed. But useful on motorways to avoid exceeding speed limits?

[hamster99]

Haven't learnt yet how to use Cruise, but did engage the limiter and found it spooky that there is no more power when you reach the set speed. But useful on motorways to avoid exceeding speed limits?

It's a speed limiter so it's designed to not exceed the speed you set, even if you want it to.
There is a safety feature which overrides the limit if you jam the accelerator to the floor (there's a switch there) so that you can get out of trouble if needed.

[PompeyLad]

Yes, the limiter is the other function of the cruise control system.
Haven't found the need to use it though, the real benefit is from steady cruising.

It's easy to use; you turn the bezel down and press in the end button on the stalk when you're at the speed you want. The car controls at that speed unless you a) press the button again b) accelerate or c) brake. If you accelerate, the selected control speed remains and will flash. If you then take your foot off the accelerator the car will drop back to the selected speed and carry on controlling. You alter the controlled speed by the top and bottom finger presses on the control arm.

But what actually inputs the fuel signals to control and supply power when required? That's the problem here.

[VertVega]

... On my last trip, however, I found that on the steeper climbs (French motorways, so not desperate stuff!) the selected speed gradually drops off....

Several times I admired how fine the cruise control of my C5 II works. It works smoothly and keeps up perfectly with the speed setpoint. Passenger never knows if the cruise control is set ON or OFF. Of course I compare all this with my previous car Xantia's cruise control Usually I don't use the cruise control if I am driving a rental car. Never used the speed limiter function in C5 II. I think it's an "useless" feature.

French highway sections like Lille -> Paris and Paris -> Reims -> Metz have been tested with no complaints. Also a bit more steeper climbs between Innsbruck (Austria) - Bolzano (Italy) have also been tested Mine is a 2 l petrol engine and I use only E98 or E100 as sold in some countries.

[wheeler]

strange one this, the first thing I would do here is make sure the injection ECU software is updated to the latest version, if you have an autobox this should also be updated at the same time.

[Richard Stevens]

Thanks, Wheeler; yes it is strange, and I shall monitor it closely on my next trip. Like VertVega, I've previously found it amazingly accurate and reliable - it's a great feature.
Should the 'injection EGU software' need updating? I mean I haven't taken the car to any workshops where it could get corrupted, so should it need any action?
But I will run it into a local workshop, they may have encountered it before.
It's as if it's not trying hard enough. It recovers as the hill levels out, so it seems it's simply not opening the throttle enough.

[DickieG]

One possible issue is that someone has been there before you in Lexia and altered the cruise parameters as in the amount of leeway cruise allows, normally it'll be 2 maybe 3 mph but if the setting is higher it may explain the "lazy" response of cruise.

[Richard Stevens]

Thanks, but I've had the car a couple of years and the fault, if it is a fault, has just come up in the last month or so.
No-one else has been close to it.
I'm in deepest Norfolk, but will get to a suitable garage in the next few days for an opinion or a check.
Any answer will be posted here.....

[Richard Stevens]

Well, I went to my 'nearby' Citroen garage and described the symptoms.
My man would not admit to having heard of the problem before, but said they could put the car onto their
diagnostics and see what there was.
I said I'd get more detail first, which I will when I'm off to France again in a couple of days.
As a precaution I have replaced the fuel filter, not due for another 15k miles. It was perfectly clean, so at least that's off the list of suspects.

[Bandit12]

Hi Richard

Which car is this as you have several listed. I use the cruise control on my C5 alot for motorway driving when there are average speed cameras like the A14 to the A1M and A127 in to southend. It should maintain the speed set no matter what the terrain. How often does it do this?

I have had on the rare occasion my C5 start accelerating even with the cruise control on! I simply switched it off and then back on again and it was fine. I put it down to the famous quirky citroen electrics Latest one is that using the tilt switch to close the sunroof actually then operates the slide function! Bit annoying when it rains and you want to close the sunroof to have it let even more rain in. I'll lexia it at the weekend. Point is that this seems normal behaviour for some older citroens.
Good luck with the diagnostic at the garage tho mate

[myglaren]

C5 sunroof should close automatically when it starts to rain.

[Bandit12]

I agree, it should but there ahve been a few occasions where closing the tilt has caused the sunroof to then open the slide. I've done a lexia and it flagged up a fault, something about voltage to sunroof out of range or accepted parameter. Maybe a BSI reset will help. Not a big deal but just goes to highlight that C5 electrics are a little quirky

[Richard Stevens]

Just got back from France. Cruise control working as originally reported. The car is the 2006 2.0 HDI, by the way.
Having tried various things on the trip, I can sum it up by saying that it works well when not asked to try too hard!
But give it a steep-ish incline or descent and it wanders away from the set figure. It will adjust as normal according to demands on the switches, but won't accelerate on a hill once it drops below the set speed, no matter how far you select above the set speed. Put your foot down and the power's there, though, which is reassuring.
It has improved the economy, though. I mean, why charge up the hill at 75mph when it's almost as good getting to the top at 68mph? I did a 450 mile trip at 56 mph average, at 50.3 mpg. So I'm not desperate to spend too much on fixing it!
And some commentators say the C5 has no charisma!