Hill descent control failing
 

Hello all,

yesterday it was the second time that this happened. Heavy snow storm here and I had to use the HDC. I used it really long like more then half an hour. After that time it stopped working and showed me the DSC light (yellow), parking brake light (red) and ABS light (yellow).
ABS had stopped to work and I tried to reset the system by restarting the car. That did not fix the problem but after about a quarter of an hour - still drinving down but without ABS - I could fix it with another restart.

This happened half a year ago in summer on a very steep track also.
Is that due to overheated brakes? They were still working perfect.

Maybe anybody has an explanation for that behavior.

Thanks in advance

Helmuth

I wonder if the brakes overheated and that cause the system to shut down until they cooled off?

Just curious how or where do you get to use HDC for an hour straight? That's over 5 or 6 miles of really, really, really, steep decent! I don't think HDC was intended to be use for that length of time. Agreed with Phil that it's most likely the overheated brakes that cause the system to shut down. Or your ABS modulator can be beaten up for that much usage.

Did you also have your foot on the brake whilst going down hill? The reason I ask this is that a couple of weeks ago I took my X out at night, got about a mile down the road and my dash came up with the same lights as you quoted. I also noticed that my brake lights were staying on... After investigating I realised that earlier that day my two young sons were in my car whilst I washed it,one of them must have kicked the switch unit above the brake pedal which made the brake lights stay on. This I can only think confused the car as I was driving it, thinking I also wanted to brake which resulted in the above.
I reset the switch as its on a ratched type thing and all has been well since...
Dweeb

All,

no foot on any pedal during that time. Of course it was a long time on HDC but did I have a chance? All else would have failed on that road with that amount of snow.

For the ones who thought about brake temperature: I was thinking the same until I stumbled across the question: does the car know brake temperatures? I would think no.

For me it is still unclear why that function fails after some time. And why you do not even have ABS afterwards.

Have fun,

Helmuth

In my 2004 manual it states that HDC only works in a certain range (approx. 3-15 mph). It automatically disengages when speed is over approx. 35 mph.

Also, it states that in case of HDC malfunction (HDC light can't be turned on, switch does not work) its because HDC is temporarily unavailable because brake temperature is too high.

So, the system must have a way to know.

However, it does not say you would receive those other lights if in this temporary mode. Maybe its normal to get those lights when its in this temporary mode?

EDIT: Looking at the manual again. I believe that these lights come on normally when the HDC is unavailable. The DSC seems to be related to the HDC and of course the ABS.

Manual says DSC light comes on if DSC and HDC or the xDrive all-wheel system has failed.

If the brakes are overheated would it make sense for the ABS to still be functioning? I don't know. :dunno:

ABS Controller may be the item that overheated and had to cool to restore the system/s.

Hello Zulu95,

that sounds like it would make sense.

I have a couple VERY steep and often icy sections of road on my commute home. I find that manually gearing down to first or second gear allows me to maintain a very slow and stable speed without use of HDC or brakes. Very effective.

I was just recently on a very steep hill. I was surprised that the car actually coasted down on its own without the HDC or brakes. It seems like it just locked up first gear. I have a 4.8, so don't know if the trans does something different.

What I do know that it is aggressive like no other, and when flying around, it also seems to hold gear in the power band. Which is supper cool for a big truck, especially when it holds 2nd gear for a block. Bliping the throttle gets it out of this "insane" mode.

Back on topic, what about transfer case actuator motor. There is a thread below, where the same lights turn on. Seems like the worm gear in the actuator motor fails, causing similar systems.

Next time it happens, get into some snow and floor it. See if you still have 4x4, or if only your rears spin.

http://www.xoutpost.com/bmw-sav-foru...tor-motor.html