Does HDC work if car stalled?

[Spence]

So I’ve been wondering about this for quite some time now and coincidentally I just watched a video on YouTube of the exact question I have. In the video, a fella was going up a very steep and rocky hill in a D4. His vehicle stalled and he flew down the hill backwards, went off the edge of the cliff, and rolled several times. When filming the aftermath, another fella in the convoy was saying that if you have your HDC on while going uphill, and your engine stalls, HDC will still work. Can anybody shed some light on this? Cheers guys.

[460cixy]

Yes as long as the ignition is on and hdc is turned on it works I watched the same video I think it was a big case of driver error

[Spence]

Yes as long as the ignition is on and hdc is turned on it works I watched the same video I think it was a big case of driver error
Good to know. That is quite a neat little feature. My engine has shut off on me going up a steep gravel track before, it was a simple roll backwards, but scary to know that could happen on an epic incline.

[460cixy]

Id suggest going out some place safe and testing it out

[101RRS]

While HDC may still try to work with the engine off, as with normal brakes wont effectiveness drop off as vacuum in the brake system drops off.

[101RRS]

Ok my curiosity got the better of me and as I live on top of a hill why not try it [thumbsupbig].

Driving forward down hill at 40kph - ignition off, very hard brake pedal, and when HDC is switched on - nothing as there is no power to it.

Driving forward down hill at 40kph - ignition on, and engine off, very hard brake pedal, and when HDC is switched on, it kicks in straight away and continues to work. Obviously the ABS pump by itself provides brakes pressure and no vacuum assist is needed. No vacuum assist to the foot brake but HDC continues to work well.

Driving backward down hill at 40kph - ignition off, very hard brake pedal, and when HDC is switched on - nothing as there is no power to it.

Driving backward down hill at 40kph - ignition on, and engine off, very hard brake pedal, and when HDC is switched on, it kicks in straight away and continues to work.

So as long as the ignition is turned on and HDC is selected - HDC works forward and backwards even when the engine is not running.

Garry

[Macadamia]

maybe I'm misunderstanding your post (or I have the wrong idea completely) but I thought HDC worked when not brake is being applied and stopped if you put your foot on the brake.

[101RRS]

maybe I'm misunderstanding your post (or I have the wrong idea completely) but I thought HDC worked when not brake is being applied and stopped if you put your foot on the brake.

Simply as part of the test I did - I also tested to see how quickly I lost the vacuum on the foot pedals - just highlighting that when ignition is on but engine is off you loose your brakes but HDC still works and does not need vacuum to work. Remember with HDC on and the engine running, you can still drive through it and you can still use your brakes if you want too. When driving along on a track with HDC on - it will kick in as soon as you lift the throttle but if you push the throttle down you can drive through HDC but it is still on but not activated - foot off and it kicks back in.

Personally I rarely use HDC as the constant shuddering and noise annoys me and I have found that low range, first gear where the torque converter locks and no throttle, means the car travels down very steep hills at about the same speed as the slowest HDC setting.

Garry

[DieselLSE]

Personally I rarely use HDC as the constant shuddering and noise annoys me and I have found that low range, first gear where the torque converter locks and no throttle, means the car travels down very steep hills at about the same speed as the slowest HDC setting.Garry
I never use it downhill either, for exactly the same reason. However, I switch it on for steep uphill climbs (low range of course) as an insurance policy should the engine stall. I also find that leaving the Terrain Response in Normal and selecting gears manually (Command Shift mode - everything is a "mode" these days!) works best for me and the type of terrain I cross. It's a pain having to remember to switch off Dynamic Stability Control each time you start the car and, when travelling in hilly country, to keep switching off HDC once you've finished climbing and switch it back on again as you reach the next steep climb.
Still, it's nice to comfortably negotiate the roughest tracks without spilling any champagne!

[Discodicky]

I never use it downhill either, for exactly the same reason. However, I switch it on for steep uphill climbs (low range of course) as an insurance policy should the engine stall. I also find that leaving the Terrain Response in Normal and selecting gears manually (Command Shift mode - everything is a "mode" these days!) works best for me and the type of terrain I cross. It's a pain having to remember to switch off Dynamic Stability Control each time you start the car and, when travelling in hilly country, to keep switching off HDC once you've finished climbing and switch it back on again as you reach the next steep climb.
Still, it's nice to comfortably negotiate the roughest tracks without spilling any champagne!

I realise that it is preferential to switch off DSC when sand driving but I am interested why do you do it for hilly country, and also why do you switch HDC off and on all the time?
Can't you just leave it on to simplify matters?
I've not done serious 4WDing with my D4 so am very interested in people's driving mode choices.

[Spence]

Ok my curiosity got the better of me and as I live on top of a hill why not try it [thumbsupbig].

Driving forward down hill at 40kph - ignition off, very hard brake pedal, and when HDC is switched on - nothing as there is no power to it.

Driving forward down hill at 40kph - ignition on, and engine off, very hard brake pedal, and when HDC is switched on, it kicks in straight away and continues to work. Obviously the ABS pump by itself provides brakes pressure and no vacuum assist is needed. No vacuum assist to the foot brake but HDC continues to work well.

Driving backward down hill at 40kph - ignition off, very hard brake pedal, and when HDC is switched on - nothing as there is no power to it.

Driving backward down hill at 40kph - ignition on, and engine off, very hard brake pedal, and when HDC is switched on, it kicks in straight away and continues to work.

So as long as the ignition is turned on and HDC is selected - HDC works forward and backwards even when the engine is not running.

GarryVery cool, well done.

[101RRS]

I realise that it is preferential to switch off DSC when sand driving but I am interested why do you do it for hilly country, and also why do you switch HDC off and on all the time?
Can't you just leave it on to simplify matters?
I've not done serious 4WDing with my D4 so am very interested in people's driving mode choices.

I will leave DieselLSE to answer for himself but for me, DSC if it comes on at the wrong time it will cut power if it detects sideways movement so I leave it off - noting that the car will override this 'DSC Off" setting in extreme circumstances like too much power.

As far as HDC is concerned - in extreme damp steep conditions I do use HDC just to be safe. If you leave HDC on and you are going relatively slow, if you take your foot off the throttle the HDC may very well activate and bring you to a screaming halt pretty quick - a bit disconcerting. So I normally have it off as indicated above - but in tight technical sections particularly going up steep hills I might have it on. You really dont want a runaway backwards if you stuff things up.

So like most settings there is a time to use and a time not to use and everyone has their own preferences - there is not one answer.

[DieselLSE]

I realise that it is preferential to switch off DSC when sand driving but I am interested why do you do it for hilly country, and also why do you switch HDC off and on all the time?
Can't you just leave it on to simplify matters?
I've not done serious 4WDing with my D4 so am very interested in people's driving mode choices.
DSC: There's been a few occasions where the engine seemed to "die" for no apparent reason. Remember that hilly country still has patches of loose surface like dust, shale, little rocks etc., plus snow and clay and whatever. I just don't need the car thinking that I'm about to go careening off in a slide when all I'm really doing is preparing for the terrain a few metres in front.
HDC: If the car thinks you are driving too fast it applies the brakes. In hilly low range country you often get little dips that you are happy to let the car run on into (maybe flick it up into 4th or 5th) as you can see that a rise is a few metres ahead and the path is smooth. Or you crest a washout and face a steep immediate descent of a metre or two. In such cases, whilst you can see and adjust to what's ahead, the reactive HDC can't and wants to pull you up. The system is very heavy on discs and pads and, as 101RRS says, you just don't need it: low range with a locked torque converter and diesel engine braking ('though I admit I'm not sure if this is actually a factor anymore with modern engine management) does a perfect job on the steepest of declines. You can set the speed at which HDC operates and you can do it on the fly but I've never bothered playing with it I must admit.

FYI, I find that on most inclines, third low is my preferred gear, allowing me to shift up and down as appropriate.

[Spence]

DSC: There's been a few occasions where the engine seemed to "die" for no apparent reason. Remember that hilly country still has patches of loose surface like dust, shale, little rocks etc., plus snow and clay and whatever. I just don't need the car thinking that I'm about to go careening off in a slide when all I'm really doing is preparing for the terrain a few metres in front.
HDC: If the car thinks you are driving too fast it applies the brakes. In hilly low range country you often get little dips that you are happy to let the car run on into (maybe flick it up into 4th or 5th) as you can see that a rise is a few metres ahead and the path is smooth. Or you crest a washout and face a steep immediate descent of a metre or two. In such cases, whilst you can see and adjust to what's ahead, the reactive HDC can't and wants to pull you up. The system is very heavy on discs and pads and, as 101RRS says, you just don't need it: low range with a locked torque converter and diesel engine braking ('though I admit I'm not sure if this is actually a factor anymore with modern engine management) does a perfect job on the steepest of declines. You can set the speed at which HDC operates and you can do it on the fly but I've never bothered playing with it I must admit.

FYI, I find that on most inclines, third low is my preferred gear, allowing me to shift up and down as appropriate.
I agree with the low range doing a good job, without needing HDC. But I have 32 inch tires, and find that now low 1st is a little bit too quick in some circumstances.

[Spence]

Fun fact... The fella in the video who rolled was wearing a AULRO T-shirt

[kelvo]

Fun fact... The fella in the video who rolled was wearing a AULRO T-shirt
Here is the original thread on the incident, where the driver comments on what happened D4 Rollover (https://www.aulro.com/afvb/l319-discovery-3-and-4-a/258994-d4-rollover.html)

[SimmAus]

Fun fact... The fella in the video who rolled was wearing a AULRO T-shirt

Fun Fact....that’s cos the fella is on AULRO. Re reading my comments...yep, that’s what happened.

[RANDLOVER]

DSC: There's been a few occasions where the engine seemed to "die" for no apparent reason..................

HDC:.............................You can set the speed at which HDC operates and you can do it on the fly but I've never bothered playing with it I must admit.

FYI, I find that on most inclines, third low is my preferred gear, allowing me to shift up and down as appropriate.

I've only stalled the D3 once, I was out exploring tracks and came to a gate on a bit of an incline, so I decided to let it roll back a few metres to a place where I could turn around, but I forgot it was still in 1st, so it stalled.

The crucial part about HDC on the fly I want to know is, will it come on if you press the button after it has stalled, in case things go wrong?

Re: driving in low range, if you think it is going downhill too fast, let it roll a bit until the torque convertor locks up, that really retards it, or at least that is what I think happens from my experience.

[101RRS]

The crucial part about HDC on the fly I want to know is, will it come on if you press the button after it has stalled, in case things go wrong?

As long as the ignition is on - when you switch HDC on it will come on - but at the speed setting it is set too.