This happens periodically. Crawl control typically engages and operates nominally. But---Routinely the system kicks out of crawl control on a downhill. Temperatures are 15F, I am going down the last quarter mile section of paved driveway and I set it to Rock and a speed of 2. That means I don't want to tolerate any slippage and the speed of 2 minimizes the anti lock brake action. I am on hard pack plowed snow and ice. The slope is very steep. Going up in the dry the LC wants to stay in 1st gear in hi range---so seriously steep. I drop an eight of a mile without drama and suddenly it hits the escape key and turns off crawl control. Is it over heating? Anti lock sounds are minimal. I don't think it is a time out. It is just few moments before it disengages. Typically only happens on severe grades. I could select something other than Rock but if it gets loose I will barrel roll a few times before finding the creek. I prefer control. Just riding the brake in 4LO and 1st gear tends to let the truck speed up too much. I am running Blizzacks and almost anything else is just a joke. So the question is why.
Crawl Control Overheating?
- Thread starter chilibit
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I haven't used crawl in this way or to this extent. Pretty interesting use of the system.
I can only guess why it's kicking out. How long or how far is the system operating before it kicks out? You said it doesn't feel like a time-out, so it's probably inconsistent how far it goes?
While 15F sounds cool enough to keep everything cool... The brake pump (actuator) is likely the thing that's performing a lot of work and building heat.
When it kicks out, I assume there's a buzzer? And does crawl blink then turn off? And perhaps the trac off light is then illuminated?
Here's the conditions the manual states for kicking off:
I can only guess why it's kicking out. How long or how far is the system operating before it kicks out? You said it doesn't feel like a time-out, so it's probably inconsistent how far it goes?
While 15F sounds cool enough to keep everything cool... The brake pump (actuator) is likely the thing that's performing a lot of work and building heat.
When it kicks out, I assume there's a buzzer? And does crawl blink then turn off? And perhaps the trac off light is then illuminated?
Here's the conditions the manual states for kicking off:
- When the Crawl Control system is operated continuously
- If Crawl Control is used continuously for a long time, the buzzer will sound, a malfunction notification will be displayed on the multi-information display, the Crawl Control indicator will go off, and Crawl Control will be temporarily inoperable as a result of the brake system overheating. In this event, stop the vehicle immediately in a safe place, and allow the brake system to cool down sufficiently until the “TRAC OFF” on the multiinformation display goes off. (In the meantime, normal driving is possible.)
- If Crawl Control is used continuously for a long time, the buzzer will sound, the system will be temporarily canceled, and a malfunction notification will be displayed on the multi-information display as a result of the automatic transmission system overheating. Stop the vehicle in a safe place until the display goes off.
These conditions may cause the system not to operate properly
When driving on the following surfaces, the system may not be able to maintain a fixed low speed, which may result in an accident:
• Extremely steep inclines.
• Extremely uneven surfaces.
• Snow-covered roads, or other slippery surfaces.
• Extremely steep inclines.
• Extremely uneven surfaces.
• Snow-covered roads, or other slippery surfaces.
Markuson
SILVER Star
You might be remembering that weird off-camber portion of the trail up Red Cone in Breck.
Not sure, but it wasn't shutting crawl off like what he describes. I haven't personally seen that. I'm also not accustomed to using crawl on down-hill (maybe once somewhere?)...
Though it does work pretty well...I personally find crawl control kind of annoying because I hate not having control over the trottle, momentum, etc. That's one thing crawl won't do--is identify where a burst of momentum would do it. It wants to feel its way up and over instead of doing a bump-over. That's where I really miss lockers... where you end up hanging (or nearly hanging) & spinning a wheel in soft spots . Or sometimes almost hanging two wheels on opposite corners. Crawl really does work well, but I wish for full control in those spots.
- Thread starter
- #5
The excerpts from the manual--- a flagrant oversight on my part as I did not look at it. Arrgh.
This happens fairly quickly. Leave building, go a quarter mile and start the drop to the gate. System pukes in 1/8 mile. When it happens to you it is surprising because your sense is that you have not stressed the systems at all. Downhill control with crawl control reduces tire slippage considerably over me doing the modulation. And I think I am pretty good. It is better. I think because it brakes a specific wheel while my foot on the petal is less specific. While I do acknowledge that it is steep it it disappointing not to be able to go down a paved driveway. I don't even get to the scary parts before it takes a hike. I have tried a short pause and retry. The time of engagement is even less which is understandable. I wandered around Ouray on my own for a couple of weeks last year. No issues. But I did not descend with crawl control. It makes you wonder just how much extra is going on in crawl control mode vs just feathering the brake in 4LO 1st gear. Must be quite a lot for the heat to build up so quickly. I'm not sure that my technical grip on the systems is as good as I imagined.
I appreciate the thoughts. I wonder if it pitches an OBDII code when this happens. I suspect not. It is working as designed. I just wish it was more robust. A lot more robust.
Rereading some of the comments: I don't remember a buzzer warning but I do get center display messages and your heart jumps up into your mouth, you stab the brake and if all is well you stop in a straight line. This is the best scenario, the others are much worse. I am just trying to go to my mailbox for Pete's sake. Oh well, it's a story and a part of the LC lore I guess. I need to learn more about the pumps in the system. I suspect I am stuck with it the way it is but then I might appreciate why.
This happens fairly quickly. Leave building, go a quarter mile and start the drop to the gate. System pukes in 1/8 mile. When it happens to you it is surprising because your sense is that you have not stressed the systems at all. Downhill control with crawl control reduces tire slippage considerably over me doing the modulation. And I think I am pretty good. It is better. I think because it brakes a specific wheel while my foot on the petal is less specific. While I do acknowledge that it is steep it it disappointing not to be able to go down a paved driveway. I don't even get to the scary parts before it takes a hike. I have tried a short pause and retry. The time of engagement is even less which is understandable. I wandered around Ouray on my own for a couple of weeks last year. No issues. But I did not descend with crawl control. It makes you wonder just how much extra is going on in crawl control mode vs just feathering the brake in 4LO 1st gear. Must be quite a lot for the heat to build up so quickly. I'm not sure that my technical grip on the systems is as good as I imagined.
I appreciate the thoughts. I wonder if it pitches an OBDII code when this happens. I suspect not. It is working as designed. I just wish it was more robust. A lot more robust.
Rereading some of the comments: I don't remember a buzzer warning but I do get center display messages and your heart jumps up into your mouth, you stab the brake and if all is well you stop in a straight line. This is the best scenario, the others are much worse. I am just trying to go to my mailbox for Pete's sake. Oh well, it's a story and a part of the LC lore I guess. I need to learn more about the pumps in the system. I suspect I am stuck with it the way it is but then I might appreciate why.
- Thread starter
- #6
A follow-on question: When you have heard the signature braking engagement sound during crawl control have you ever had the sense that it was activated on the rear axle? My hearing is not bat-like but I don't recall ever feeling that engagement sound was coming from the rear. Always from the front. Up hill or down hill it does not matter. I have used it a thousand times at least.
Good question. The noise is always up front in my experience. I believe the clickety/clackety noise is largely coming from the ABS system and brake actuators which are mounted underhood. The brake calipers themselves likely don't make any noise. Just the system that hydraulically drives the calipers.
- Thread starter
- #8
"brake actuators which are mounted under-hood"
That makes sense of it. Learned something new.
If you drop down a mountain, say in Colorado, in Hi Range and you are forced to use a heavy brake for an uncomfortable distance---you never hear the actuators. Yet, an eighth of a mile on a 25% slope in crawl control brings it to its knees. I remember having brakes on fire dropping into Vienna, Austria once. It left an impression. My VW bus had precious little compression braking. Usually we think of pads/rotors and then boiling brake fluid if we did not set the car up properly for a particular track --- but not actuators. I think that if a car has anti-lock it must have an actuator to pump the brake. I am trying to connect the dots and I am a bit short of understanding. An all too frequent occurrence for me.
That makes sense of it. Learned something new.
If you drop down a mountain, say in Colorado, in Hi Range and you are forced to use a heavy brake for an uncomfortable distance---you never hear the actuators. Yet, an eighth of a mile on a 25% slope in crawl control brings it to its knees. I remember having brakes on fire dropping into Vienna, Austria once. It left an impression. My VW bus had precious little compression braking. Usually we think of pads/rotors and then boiling brake fluid if we did not set the car up properly for a particular track --- but not actuators. I think that if a car has anti-lock it must have an actuator to pump the brake. I am trying to connect the dots and I am a bit short of understanding. An all too frequent occurrence for me.
Right. The crawl control system does operate a bit differently than our foot. Like ABS, it pulses the brakes. So instead of a single smooth brake application, it breaks up the braking event into multiple small brake applications. Lots of digital systems work in this fashion, known as pulse width modulation (PWM). It's a simplification for digital systems that operate on an on/off principle, to simulate fine motor control. And with that, comes a bunch of jarring on/off impulses and noise.
So the system is very busy pumping up hydraulic pressure, and madly applying brakes on/off, on a per wheel basis, as it attempts to simulate fine control.
So the system is very busy pumping up hydraulic pressure, and madly applying brakes on/off, on a per wheel basis, as it attempts to simulate fine control.
- Thread starter
- #10
Yes, I think the width of the pulse is fairly short. And there is a pressure drop after each pulse application unlike my mountain example. That ramps up pumping heat. I am surprised this does not come up very often. I appreciate the thoughts. For me it is a weak link in the chain. On the other hand, I seem be out beyond 4 standard deviations. I can "drive around it." Ciao
Markuson
SILVER Star
I'd wager most of us only tend to use Crawl for very short distances...so maybe it just hasn't come up. I rarely engage mine at all, and if I do it's usually for one specific spot of maybe a few yards of travel up and over something that leads to wheel spin. So who knows... Maybe we'd all report issues if left in crawl for a quarter mile down-hill... ?
- Thread starter
- #12
Markuson: That seems a perfectly reasonable position. I use it for a mile or less around the perimeters when I am looking for coyote and it is fine. Ironically, I don't really NEED it then, it is just a convenience so I can ignore the terrain somewhat and pay attention out the window. You used the word momentum earlier. On ice downhill I am looking for zero momentum. Well, almost zero. Most folks would see the world your way and my 40 liked a bit of moment occasionally. IH8MUD members have been generous with their comments and avoided being judgemental. That is a good thing. Good forum. Good people.
Markuson
SILVER Star
Of course you're right about not wanting momentum on a downhill. Certainly you are specifically needing to AVOID momentum on a slippery downhill...so no disagreement at all there.
I was referring only to my more typical use of crawl...where I am losing traction getting up and over an obstacle. That's where momentum is often needed for that extra bump...
