Sensation of braking when going downhill

[damianscott71]

I had a real bad bout of loss of power yesterday on a country road, crested a hill and went to put my foot down, it felt like I'd put my foot on the bloody brake (it was THAT pronounced)....... It was really distracting and would have been quite dangerous had I been attempting an overtake. I might get in touch with one of the car mags and have them chase VAG for a qualified response.

[Wet Kipper]

glad I found this thread and it's not just my new Blackline.

My commute is over many hills on a country road, so this "feature" has plenty chances to show itself.

seems to only happen when using light throttle to go downhill. putting the clutch down to coast stops it, and accelerating hard seems to override it, but most of the hills i go down have sharp turns at the bottom so you don't really want to go storming down.

Doesn't happen in my 1.4 Tsi Octy, never had it in my Fabia vRS diesel

[zacherynuk]

If the road feels skitterish then ESP will apply some braking to one or more wheels. ESP cannot apply power.

When driving within the envelope; "Skitterish" most often happens when you are not applying power to the two front wheels, eg going down an decline or coasting over an uneven surface.

The ECU does not apply fuel to the engine if the engine is in gear and under revved (decelerating) - this is an awesome fuel saving feature many do not appreciate and contributes solely to the figures more than you realise! (basically leaving in gear when decelerating to a junction uses less fuel than neutral)

So if you are heading down an incline without positive power, then the system has to adjust for every little flex, bump and change of rotation of the tyre - it can only do this, by design, by applying light braking - it then knows what it did is changing things the way it expected. If it didn't do this it wouldn't have any 'expected' telemetry and wouldn't know what was happening or what it was capable of if it had to step in to (for example) save your life. This is, as you have pointed out wasted energy which decreases your speed, but without it the system may njot have enough information to ensure it can properly stabilise the car.

The worse the bumps the more the braking. The worse your balancing, tyre wear or geometrical setup, the worse the effect. This includes dissimilar inflated tyres - both front and rear - not just side to side.

I think.

Turn your ESP off and see.

Edited 9 March, 2013 by zacherynuk

[stever750]

I'm not sure esp has to go through some kind of learning mode. AFAIK it uses the abs sensor information plus yaw, and steering angle info to assess whether the vehicle is skidding or not. The system doesn't need to check the envelope, it's already programmed.

Sent from my GT-I9300 using Tapatalk 2

[Fatbloke]

Octy cuts the throttle when you touch the brake so you can't left foot brake or dry the brakes after going through water.

The brakes have a wiping function that regularly 'dabs' the pads onto the disc when you have your wipers on, effectively keeping your brakes dry automatically

[zacherynuk]

I'm not sure esp has to go through some kind of learning mode. AFAIK it uses the abs sensor information plus yaw, and steering angle info to assess whether the vehicle is skidding or not. The system doesn't need to check the envelope, it's already programmed.

Sent from my GT-I9300 using Tapatalk 2

Ahh fair enough, though I was thinking about the uneven surface for that bit, though I guess you would notice the yellow light flicker...

The Engine management ceasing all petrol and power to the engine would be enough to slow the vehicle down under normal circumstances of in gear foot off decline, was my primary not well made point

[dbayman]

My Octy 2.0 CR does exactly the same and has done since new. Spoke to the head engineer when it was serviced and he said he had never heard of this type of problem before. To be fair I mostly only see it at one particular spot where after going through a double roundabout there is a downhill dip for about 100 meters. It always happens there it's as if the fuel was cut off for a second or so. I was pretty certain it was a feature of the engine management system so I didn't press to get the issue resolved.

It is great to know that it is indeed a feature of VAG cars

[nickguzzi]

Disc brakes are designed for the pads to be "just" touching the disc surface.  This was found to keep the disc clean and ready for action at all times with no detriment to braking efficiency.  Customers also complained if the discs looked rusty.

Ford did a lot of work in this area after a bit of a problem with brake shudder on one of the later model Cortinas.  Its was widely thought to be discs "warping".   It turned out to be slight varitations in braking surface composition.  The constant contact sorted it - they claimed.

[Phildo]

Hi All,

Searched the forum and found this thread.... exactly what has started to happen with my car! Octavia VRS Tdi CR 170.

 

Anybody got anywhere with this issue? I swear it has just started in the last month with my car and wasn't happening before. (Had it since August)

 

I can't believe it is anything but a fault. If it's a feature, it's ****, annoying and bordering on dangerous. It's NOT the ESP

 

Can anyone shed any light. Please please? 

[WookieeM]

I think everyone who has experienced it has learnt to live with the 'feature'

Mine does it but only over crests never any other time.

On one route home it does it every time, but never at any other point during normal driving.

If you can replicate the issue on the same stretch of road a few times then it's prob not an issue.

If it's random or happening on smooth downhills ie not over crests then may be something else.

[philbes]

My car, a FL Octavia vRS CR DSG, does not exhibit the behaviour being discussed.  I live in the Cotswold so regularly drive over the crests of hills.  Next time I'm driving I will try accelerating just before a crest and see if I can invoke what has been described.

 

If travelling downhill a light touch on the brakes will induce the DSG to change down a gear (or two) but I see changing down on a downhill run, rather than constant braking, as good driving technique.

[Phildo]

It's just over crests with mine so it seems to be the common issue. I'm 99% sure that this is a new thing because I'd not noticed it until a few weeks ago. I live on the edge of the lakes and so I'm surrounded by undulating roads. I WOULD have noticed! One day I felt it and thought "what the hell was that?" I just put it down to a blip in the fuel delivery and hoped it would go away. It hasn't and it's annoying me.

Seems to be when at a constant speed so if you've got your foot off or down it doesn't do it

[Exportio_vRS]

My 10 plate FL vRS doesnt do this when driving using normal throttle, however it does when I am using cruise and i go down a hill, you can feel slight braking to maintain the cruise speed.

[RainbowFire]

My 10 plate FL vRS doesnt do this when driving using normal throttle, however it does when I am using cruise and i go down a hill, you can feel slight braking to maintain the cruise speed.

 

Cruise doesn't apply the brakes, it will only shut the throttle right back to reduce speed.

[_redders_]

I have this in mine, thought I had warped front discs as I only get it when braking downhill to a stop, tested my theory last night coming off the m62 at 90mph, jammed the brakes on, car braked in a straight line with no back pressure/pulsing off the pedal until it got to about 10mph then I felt it pump again, doesn't bother me, I've learned to live with it, although I might try it with the traction control off and see if that makes a difference, can't see why it would.