Hello. My 2005 Sport 2.7 V6 diesel has developed a fault which is puzzling me and I am hoping for wisdom from here. After start up, when I press the brake in order to select drive, the two amber warning lights for HDC and stability control come on, accompanied by a "bong". The dashboard display says "HDC fault system not available" and the ride height control shuts off, sometimes seeming to dump the air from the air bags. At the same time the brake lights at the rear do not work. If I am driving when the fault occurs, still initiated by touching the brake pedal, a third amber light for dynamic response also comes on.

If I switch off and back on again, it clears until I touch the brake again. Weirdly, this is intermittent and it has happened before, but then righted itself. It has not done it for about a year, but it now does it all the time.

I am suspicious of the brakelight circuit, but the bulbs light up fine when the fault is not occuring. I did wonder about the brake light switch. Or is it something more substantial? The fact that it is intermittent makes me think that a poor connection somewhere may be involved.

All advice gratefully received !

Adam..

All the symptoms of the rear brake switch. Cheapest option to try first as well.

Thanks. I think I will give that a try as a first step, unless anyone has any further thoughts?

I have found that if I switch off, then switch on again and immediately press the ride height adjustment the suspension will reactivate and the fault will clear, but as soon as I press the brake pedal, the fault reoccurs with amber warning lights and no suspension or special programmes. Since all this happens before it is even possible to engage drive, and the brake lights stop working at the same time, I am suspicious of the brake light switch.

I will report back on what I find.
Adam..

Brake light bulbs will also cause this fault. Even cheaper and easier to try out.

Unplug the back lights, and see if the fault still occurs

Thanks DM.

At the moment, all bulbs light up if I try pressing the brake pedal before starting the engine and I have never changed a bulb on it. However, I will have a look tonight and see what happens if I disconnect the bulb holders.

What I find strange is that the bulbs light up as I said above, but as soon as the fault is detected the brake lights don`t work either.

I had better see what I find tonight. I may be back !!

The reason a brake bulb or switch throws up a HDC error and some other errors is that the HDC relay is hardwired in to the brake light circuit. This is because HDC activates the brake lights when HDC is controlling the vehicle's speed. An error in the circuitry means that HDC doesn't know if it's able to work properly so it throws the error. Terrain Response uses HDC so a fault on HDC will cause a fault in TR.

One of the side effects of having all of the systems so closely linked is that you can get a cascade of errors caused by a simple issue like a blown bulb or a dodgy brake switch. It's annoying, but when you've experienced the systems working properly to control 2.5 tonnes of 4x4 on a steep, slippery gardient you realise it's a brilliant system. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Ahh, that helps clarify my thinking. Thanks very much.

I will check out the bulbs, switch and associated wiring and see where I go from there.

Thanks again
Adam..

Well explained RRSTDV8 Just what i was going to say.

Well, I set about Black Bess with all the intentions of changing the brake light switch when I made a shocking discovery.

With the HDC/everything else fault registered on the dashboard (and brake lights not working you will remember), I pressed the brake pedal with my hand (engine running) whilst looking at the switch. I heard an impressive gurgling sound from the brake fluid reservoir. At least i think it was there as my head was in the driver`s footwell.

After that, I switched off and back on again and the fault was cleared and stayed that way for the next 20 miles.

It come back this morning, but again, I pressed the pedal, to get the bubbling from the reservoir, which incidentaly goes on indefinitely if you hold the pedal down, and sure enough the fault cleared again.

Throughout all this, the pedal feels normal and the brakes are fine, indeed it only passed the MOT last week.

Now, my question to you LR experts is this:- Is the servo supplied with vacuum or compressed air? Could it be air and I have a split servo diaphragm which is letting air get to the end of the master cylinder, which, when the piston is forward because of the pedal being pressed, is allowing air into the fluid reservoir????

I can`t think what else could be causing what I have got, nor how the fault is being sensed, or why the brake lights go out, but come right back when the fault is cleared.

It is all very rum.

Anybody heard of anything similar?

Adam..

Has it had the brake vacuum pipe recall done to stop oil entering the servo?
Regards
Barry 2017 Range Rover Sport TDV6 L494 SE Fuji White
2011 Range Rover Sport SDV6 L320 SE Fuji White Loved but GONE
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Ex Member Range Rover Club NSW

http://www.rrsport.co.uk/forum/topic16517.html before you ask where to find info about the servo recall...  2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Black Bess wrote:

Now, my question to you LR experts is this:- Is the servo supplied with vacuum or compressed air?

You took the words right out of my mouth RRSTDV8! My car was first registered on 01/09/2005, so it seems to pre date the recall. I certainly never received any notification.

And it is a vacuum pump and conventional servo, so that clears that up, thanks.

I will have to investigate further at the weekend, when I can get my wife to press the pedal whilst I rummage about under the bonnet.

I have never seen anything quite like this before.

Adam..

I have brought this back up to the top in the hope that someone with similar experiences can shed any light on the problem. I have yet to get into it in earnest, but the fault is still there, as described above and is really, really annoying!

Adam..

Black Bess wrote:

You took the words right out of my mouth RRSTDV8! My car was first registered on 01/09/2005, so it seems to pre date the recall. I certainly never received any notification.

And it is a vacuum pump and conventional servo, so that clears that up, thanks.

I will have to investigate further at the weekend, when I can get my wife to press the pedal whilst I rummage about under the bonnet.

I have never seen anything quite like this before.

Adam..

Ignore the fact that it pre dates the re-call, ALL were affected and you should test the servo pipe for oil in it. If oil is present, get it to a Dealer and they should sort the problem out.  Bodsys Brake Bible
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