Cruise Control cutting out at certain speed

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

User avatar
patriotbarrow
Posts: 21
Joined: 18 Sep 2017, 12:01
x 1

Cruise Control cutting out at certain speed

Post by patriotbarrow »

Hello, everyone!

Got a bit of a head-scratcher for you today. Usual google searches turned up empty. Will probably end up having to get it diagnosed, but money's really tight due to the pandemic, so I figured I'd try my luck here.

Got a 2009 C3 Picasso 1.6 HDI 109 that likes to cut out its cruise control when going at a certain speed. I haven't been able to determine the exact number, but it's at around 100 km/h (60 mph). The cruise and/or limiter readings on the dash turn into "- -" and ignores any other inputs on the cruise controls until I stop and restart the engine. Cruise control works normally as long as the car is under the cut-out threshold. The cut-out depends on vehicle speed, not on selected speed value in cruise/limiter settings.

Things of note and things I have tried:

- faulty BSI changed last year, replaced with new unit (if at all relevant) and updated to latest firmware as of April-ish 2019.
- wiggling, pushing or moving clutch or brake pedals did not help.
- have changed the brake switch as it was touted as the most common problem. Did not help.
- squirted a small amount of contact cleaner on cruise control switches and fiddled with them for a bit. Did not help.

Apart from changing the clutch switch, I'm out of ideas. Anybody ever had similar issues?

Thank you!

User avatar
GiveMeABreak
Forum Admin Team
Posts: 21577
Joined: 15 Sep 2015, 19:38
x 2163

Re: Cruise Control cutting out at certain speed

Post by GiveMeABreak »

There's a reason for this:

The engine ECU has detected a fault with the system and is therefore going into a backup mode. The result of which is reduced engine power (to prevent damage whilst the fault is in effect) and another consequence is deactivation of the speed control functions (cruise control and speed limiter).

That's why when the fault kicks in, you have a maximum amount of engine power available and the cruise function is disabled. When the car is stopped, ignition off and restarted, the fault resets and speed functions are allowed again (cruise) - that is until the fault happens again.

So you will need to get it diagnosed to find out what the fault code is, which will give us a better idea. Without this there could be a hundred reasons and they will all be pure guesses. You don't want to be changing parts and spraying anything anywhere - there is a specific reason for the fault and it needs to be identified and fixed.

Be aware that you will have limited engine power when the fault is active - so you will not have the full power of the engine for overtaking or in an emergency - so be aware of that and drive accordingly until you can get it fixed. :wink:

If you don't have Diagbox and your own diagnostic code reader, you can always ask friends if they have a code reader. Generic third party code readers can't always read all the engine ECUs nor the specific constructor fault codes so be aware of that - but it might just be able to pick up a code if it's a general OBDII code.

User avatar
patriotbarrow
Posts: 21
Joined: 18 Sep 2017, 12:01
x 1

Re: Cruise Control cutting out at certain speed

Post by patriotbarrow »

Ouch! Thank you for replying! I'm surprised to find out the car can go into limp mode without any sort of any warning light turning on. The service light came on a few times when one of the parking sensors froze, but not for something engine-related. Going to have to ask around for people with code readers. Would a professional non-Diagbox scanner have a higher chance of catching faults than a cheapo ELM Bluetooth OBD dongle?

How much of a reduction in engine power would there be? I'm asking because last weekend I drove on the motorway with a fully laden car with a headwind and AC on and the car got up to 93 mph with no fanfare.

User avatar
GiveMeABreak
Forum Admin Team
Posts: 21577
Joined: 15 Sep 2015, 19:38
x 2163

Re: Cruise Control cutting out at certain speed

Post by GiveMeABreak »

Ok, so as for code readers: most professional mechanics will have a decent code reader able to talk to most cars - that's your best bet. If not, a cheaper OBD II scanner may work - but may not - it depends on the type of fault code. That's why professional tools are more expensive as they have to be updated regularly with newer software to keep pace with newer systems and there is a cost to this.

As for the fault: The engine management light does not always come on. It really depends on the exact fault as to whether it is lit or not. Again, if the fault is a temporary fault - it may reset itself when the ignition is switched off - until the conditions arise that trigger it again. That's why you were probably able to do warp speeds the other day - the fault may not have been triggered. As soon as conditions appear that trigger the fault, engine speed will possibly be limited again and your cruise control will be disengaged.

Power reduction depends on the engine, but can be typically limited at anywhere from 2500 to 3000 RPM.

User avatar
patriotbarrow
Posts: 21
Joined: 18 Sep 2017, 12:01
x 1

Re: Cruise Control cutting out at certain speed

Post by patriotbarrow »

Oh, the cruise control was disabled with the brisk trip the other day. My point is I've had this car for a few years and I am acquainted with its power output. I don't ever feel a drop in power whenever CC cuts out.
In any case, I'll try to find someone in my area with one of the better code scanners or Diagbox if I can find any. Thanks so much for your help :)

User avatar
Doo
Donor 2020
Posts: 126
Joined: 09 Sep 2019, 16:53
x 26

Re: Cruise Control cutting out at certain speed

Post by Doo »

I'd be tempted to check a wheel bearing... Could be ABS sensor, but often times they can be affected by a worn wheel bearing. Had this few times in various cars.

Cheap check. Jack up each corner at a time and wiggle up/down & side to side.

At least that's a free test.

User avatar
GiveMeABreak
Forum Admin Team
Posts: 21577
Joined: 15 Sep 2015, 19:38
x 2163

Re: Cruise Control cutting out at certain speed

Post by GiveMeABreak »

patriotbarrow wrote:
27 Jul 2020, 13:24
Oh, the cruise control was disabled with the brisk trip the other day. My point is I've had this car for a few years and I am acquainted with its power output. I don't ever feel a drop in power whenever CC cuts out.
In any case, I'll try to find someone in my area with one of the better code scanners or Diagbox if I can find any. Thanks so much for your help :)
Without knowing the exact fault code I can't tell you for certain what the exact back up mode is. They vary - so the fault may disable speed cruise control but not limit the engine power - so that's why it's important to get the codes. Once we have those I can tell you what they mean.

User avatar
patriotbarrow
Posts: 21
Joined: 18 Sep 2017, 12:01
x 1

Re: Cruise Control cutting out at certain speed

Post by patriotbarrow »

Doo wrote:
27 Jul 2020, 22:04
Cheap check. Jack up each corner at a time and wiggle up/down & side to side.
I'd only really have to check the front; the wheel bearings on the rear were replaced in March along with the brake disks.

Buuuut a tester would probably yield a better result.