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Scenic accelerating at max revs by itself

18K views 22 replies 9 participants last post by  theengravingartisan 
#1 ·
Good evening forum,

My apologies if I am posting this in the wrong section but I would be grateful for some advice.

A little background first... I purchased my ex mobility Grand Scenic (10) 1.5 dCi Dyn last thursday from a independent dealer. 16,000 miles, FSH and no obvious (to a noob anyway) mechanical faults on either of my test drives.

Aside from short term clicking/typewriter after parking the car it has been a pleasure to drive. Until today.

Upon merging onto a dual carriageway, I changed gear from 3rd to 4th and the engine went into max revs for about 10 secs but returned to normal and I was able to finish my journey (nursery run) with no further problems and put it down to my inexperience of the car and diesel engines.

After picking up my kid we left the sleepy village roads and turned onto the main B road back to the dual carriageway. After I changed up from 2nd to 3rd gear the max revving kicked in again. I quickly changed up to 4th and the revving calmed down somewhat but the accelerator pedal was fully depressed (my foot was nowhere near it) and the car continued to gain speed at an alarming rate. I had the brakes fully pushed in to avoid ramming into a truck in front but this only seemed to limit the acceleration, not stop it. When I took my foot off the brake the car accelerated at high revs. After some frantic banging on the accelerator pedal and changing gears up and down the pedal eventually returned to its normal position and the acceleration returned to normal. It was quite a scary 20 seconds or so, especially with my two wee ones in the back. I arrived home with no further problems.

Does anyone have any experience of this?

I have searched online and this forum but have been unable to find a problem similar to this one except for a short thread about the pedal possibly being stuck by the carpet which is definitely not what happened in my case.

Today was the first time I drove the car without putting the keycard into the slot (had it in my pocket). Would this have anything to do with it?

Cruise control and speed limiters were off.

I would be very thankful for any similar problems experienced by GS users and how you went about fixing it.

I will be contacting the dealer tomorrow and will no doubt be told to bring the car in but it's a 30 mile drive on the motorway and I'm a little apprehensive about it.

Sorry for the long winded first post.

Thank you for your time.
 
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#2 ·
Clearly the throttle cable or its potentiometer are sticking open, there is a spring that usually closes the throttle when you take your foot off the gas but it is not doing its job. I would not be happy driving it and I am what you might call experienced mainly because of the risk of engine damaging itself as it runs away. I would insist the dealer arranges for it to be collected or sends one of his mechanics to you.
 
#4 ·
Sorry thought of another reason why you should not drive it, your car insurers require you to maintain the car in a roadworthy condition, if you have an accident they could exclude liability on the basis that you knew of the sticking throttle and should not have been driving the car in this unroadworthy condition leaving you personally liable for the damage and whiplash clams from the peeps in the car in front.....
 
#6 ·
Still trying to figure out this reply function thingy...

Got in touch with the dealer. They absolutely agreed with you Wyn about it not being safe to drive and are in the process of arranging someone to come pick it up.

They're also bringing a courtesy car so I'm guessing it could a wee while to fix.

It's annoying but I'm impressed by their level of service. I guess these things happen. Or should I be angry that they never spotted it before they sold it to me?

I'll update later.
 
#7 ·
Hi scenicfifer, I have recently bought a pre owned megane which has also heaved exactly as you describe. I have taken it to the dealer to which they can not find an issue. I am not happy to take it away till a fault is found as I drive my kids around in it. If you can remember what the source problem was I would greatly appreciate hearing how you fixed the problem. Thanks in a advance
 
#9 ·
Hi Ralph, it is a diesel but it runs very clean. It seems quite sporadic when it misbehaves. When I was driving on due carriage way at a constant speed. I felt the pedal depress itself and the speed increase. It felt like the cruse control however it was not enabled and when I pressed the break. The car fought against it and dI'd not slow efficiency. I had to press the clutch to regain control.
 
#11 ·
Sounds like a cruse control problem and as Ours says the switches on the
pedals could be the problem, have a look at them they sometimes come loose
or unplugged or just fail.
 
#12 ·
Could also be throttle pedal wiring or resistor.
Sogginess / corrosion as well.
Especially if the Cruise control is off. How about setting speed limiter to lowest setting, for if it happens again?

Curious about "feeling the pedal depress itself" as these motors are fly by wire. When I use cruise the pedal doesn't move & if I touch it, cruise automatically disengages,as it does with brake & clutch.
 
#17 ·
My first though was the turbo oil seals but no smoke so that is very unlikely,
Next thought was the cruise control pressing the clutch/brake or accelerator should disconnect this and allow the car to drive as normal, but it only responded
to the clutch and the cruise was not enabled so the run away should not have
happened in the first place so if it is the cruise what caused it to come on,
one thought is has the car been wet is there any sign of damp in any of the
fuse of relay boxes? water in any of the electronics can cause strange things to
happen, Ours mentioned the switches on the pedals, have you looked at these.
 
#18 ·
Thanks for all the input. I sent the car the dealer strait awaw as I was driving my kids and didon't feel safe. They ran there diagnostics and found no fault. This is really frustrating as it was clearly not right. That said, The breakdown technician aud he found a accelerator fault but seemed to have cleared the fault! I asked the dealer if they could speak to breakdown company to see if there was a record of the fault. To go to a comment about the pedal moving. I agree I think I may have been more showed with the car accelerating on its own and may have felt something I didn't. I was called by the dealer today to come to the garage to drive the car with the technician as they could not replicate the issue. The fault did not raise its head however. I am starting to believe it may be a bug in the programming that a exact series of events would trigger. The dealer are continuing to carry out extensive testing but fear the fault will not happen again. By biggest fear is putting my children in a car I know may do that again!!
 
#21 ·
Not saying that it wouldn't be the accelerator pedal.

But saying that I have had a similar fault. And first the dealer replaced the accelerator pedal, then they replaced the throttle body and the fault was finally found in the ECU multiplug being an intermittent contact. The ECU lost the throttle pedal signal from time to time and thought it would be a good Renault humour to go WOT for a while.

The Renault diagnostics system is really not that good in pointing out faults, especially intermittent wiring faults.

Overall, it seems like Renault cars have probably the worst electrics design and/or quality of all makes. But that's one of the reasons Renaults are so damn cheap and THAT FOLKS, is why I like these cars. I can buy it cheap and then with little elbow grease you got a working automobile.
 
#23 ·
I had the grand scenic. Had passed its vrt test. Went to visit my father, left as soon as I turned to roundabout the car accelerated on its own and brakes pedal flat and not working. I had no other choice to navigate it without injuring anybody as I was near a school but had to crash it into a parking area. I'm still not over it, cannot fathom why that happened. We traveled overland with it never gave me any problems
 
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