HDC query

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htr

htr

Well-Known Member
Posts
1,552
Location
Central Otago, Southern New Zealand
When I'm in 1st gear and I've selected HDC, as I move off I feel rapid pulsing through the brake pedal and a rather metalic rattling from in front of me. I guess it should be smooth and quiet when moving off. Do I have a problem? and where would I began to look to sort it out?
 
Thats the abs system, which is what the hdc uses to control speed going down hills

What you can hear is probably the rapid application of the brakes
 
SES88 said:
Thats the abs system, which is what the hdc uses to control speed going down hills

What you can hear is probably the rapid application of the brakes
Click to expand...

Hi SES, so is what I'm experiencing normal operation? A very rapid pulsing felt through the brake pedal and a rattling/jangling type sound from in front of the drivers side?

I stop when this happens so can't say if it ceases with a rise in road speed - worried I may damage something.

I feels / sounds odd.
 
Is it pulsing all the time you're moving? I've never tried it to be honest - but if it pulses all the time, I'd have thought that wrong.

My take on HDC is that it it attempts to maintain a speed proportional to the accelerator position. When accelerating, speed is catching up with the throttle position so no ABS pulsing activity should occur. Lifting the throttle will cause the speed to be higher than the throttle position - so engine braking will slow the car assisted by the ABS pulsing.

So I'd have thought HDC/ABS/pulsing should only cut in during engine braking. Am I wrong?

The actual speed the ECU wants to keep to the car to will be slightly higher than the throttle position - so for example at throttle rest it may try to maintain 5 KMH.
 
You're only meant to engage it when necessary, not leave it on and drive

Idea is you'll reach the crest of a hill, engage it, lift off the brakes (in gear) and let the car roll down, the HDC will then maintain a "safe" low speed without any input from the driver on the accelerator or brake
 
I've been on a better test drive. I think all is well. HDC engaged and I crept down a steep gravely track. Feet off all pedals, obviously not pulsing felt, and when the speed rises to I guess 5km/h, the ABS makes a noise like an old wooden school ruler being 'boinged' on the side of a desk, otherwise all quiet at a very slow crawl down the hill. Good to see the TC come on when on the way back up.
 
SES88 said:
You're only meant to engage it when necessary, not leave it on and drive

Idea is you'll reach the crest of a hill, engage it, lift off the brakes (in gear) and let the car roll down, the HDC will then maintain a "safe" low speed without any input from the driver on the accelerator or brake
Click to expand...

Makes sense.

You could have just said RTFM.

You LZ guys are all b***ds. :rolleyes:

htr said:
I've been on a better test drive. I think all is well. HDC engaged and I crept down a steep gravely track. Feet off all pedals, obviously not pulsing felt, and when the speed rises to I guess 5km/h, the ABS makes a noise like an old wooden school ruler being 'boinged' on the side of a desk, otherwise all quiet at a very slow crawl down the hill. Good to see the TC come on when on the way back up.
Click to expand...

Cool - did you have to hold the wire on the gear stick button? That's one of the reasons I've never played with HDC - the wire's done its normal job of breaking away :)
 
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