strange thing - Cadillac XT4 Forum
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post #1 of 14 (permalink) Old 12-06-2018, 07:16 PM Thread Starter
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strange thing

my wifes new XT4 is doing something strange.. I'm not going to explain it all right now, but.. it has my local dealer completely baffled as well as the GM tech folks..

what I would like is to ask, is, anyone else that is currently driving an XT4 to try something for me..

when you are on a fairly steep incline, stop, and put it into park.. when you put it into park, watch and see if the park brake applies itself.. both in the park brake symbol, as well as in the DIC saying "park brake set".. please try this facing both uphill, as well as down hill... then with the vehicle on a fairly level surface try it again and see if the park brake is automatically applied.. mine does not on the level, only on a substantial slope, say around a 10 degree slope..

GM says it should not be doing this, but then they're not really sure..

this is only part of the issue.. once anyone else confirms as to whether or not their vehicle exhibits the same characteristic I'll explain the rest of the weirdness..

Bernie
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post #2 of 14 (permalink) Old 12-10-2018, 06:17 AM
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I believe that it is "Hill Start Assist" (HSA).Look at page 200 of the Owner Manual.
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post #3 of 14 (permalink) Old 12-10-2018, 04:14 PM
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Yes, mine does this also. As stated above it is the "Hill Assist". As soon as you tap the gas pedal or wait 3 seconds the break releases. It auto applies the parking break I believe when you are on a hill.

Felipe
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post #4 of 14 (permalink) Old 12-10-2018, 09:37 PM Thread Starter
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appreciate the input guys but this doesn't answer my question..
I'm familiar with the "hill start assist" function but here's what I'm trying to determine..

any other vehicle I've owned hillstart assist will become active when you're on an incline (pointing uphill or downhill) and you shift the vehicle into park, but none of them would automatically apply the park brake at the same time.. this is specifically what I would appreciate any other XT4 owner to confirm for me.. does your vehicle apply park brake when you would be in a hill start assist condition and shift into park..

as I mentioned earlier there's another issue we're dealing with that could be part of the hill start assist function.. both my local dealer and GM technical don't feel the park brake should be applied automatically but are not 100% sure on that.. so before we dig much deeper it would be nice if someone could say "yup, mine does too, or nope, it doesn't"..

thx again
Bernie
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post #5 of 14 (permalink) Old 12-11-2018, 10:28 AM
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I recommend reading the Owner Manual at page 200 and follow the steps it describes. Many new models that have electric parking brake also does the same, applying the parking on any incline until you step on the accelerator. Some brands do it by locking the transmission.

I know that others, such as the Ford Fusion will automatically release the electric parking brake when you shift into "D".This is different but does represent how modern cars have some "intelligence" and help the driver. I consider the Cadillac XT4 as one of the next generation.
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post #6 of 14 (permalink) Old 12-11-2018, 08:29 PM Thread Starter
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appreciate the input Raymond but the owners manual really doesn't address my issues (page 200 included)

this vehicle does not have any forward sensing systems (adaptive cruise, pedestrian braking or even lane departure, those are all extra's on the XT4 which means extra cost)

here's the main issue.. wife backs out of the garage and into a turn around area (about a 100 feet) she then puts the vehicle in drive and starts to roll down the driveway which is about a 10 degree slope (relatively steep) because of this she has neither her foot on the brake (yet, but will soon as the vehicle accelerates) nor her foot on the gas.. at this point the vehicle is going at a brisk walk or close to a jogging speed.. the vehicle has just done an up shift, and then immediately after that a downshift, and then it lurches a couple times and brakes itself to a complete stop..

all this has been video'd and demonstrated to the service manager of the dealership where the vehicle was purchased.. GM's response is "it shouldn't do that".. this failure mode does not occur every time but probably about 1 in 5.. in the video GM technical can see everything that's displayed on the dash..

when the vehicle is in this situation (lets call it failure mode) this is what we've tried.. setting park brake with park brake switch and then releasing bark brake by pushing brake peddle.. (as the manual says) .. if you give the vehicle any gas it will creep forward but has resistance as though your holding the brake pedal.. the moment you take your foot off the gas the car returns to a complete stop.. now keep in mind the driveway in this location is steep enough that the car should be rolling like crazy.. we've also tried pressing the brake peddle firmly a number of times with no result.. the only way the vehicle can be made to "resume normal operation" is to either shift it into either neutral or park and then back into drive and then off you go..

okay so now the good stuff.. the shop foreman is in the car, scanner plugged in and he's ready for anything.. car goes into failure mode and he see's nothing on the scanner.. he searches through all the BCM's and nothing.. so now I put the vehicle into park and the dash displays the park brake symbol as well as the DIC saying "park brake set".. the only problem is the scanner says it isn't.. it says that the park brake switch is "applied" but non of the park brake components are active.. we tried this a number of times with the same results.. if you applied the park brake yourself by utilizing the park brake switch the system worked as advertised, but if you got the "park brake applied" indication when in the hill assist situation it was in fact not..

So now GM Technical has the video's, scanner snap shots from the dealers service people and the questions about why does the park brake say it's set, when in fact it's not (according to the dealers expensive scanner).. and here is what GM has come up with to date..

they want the dealer to check for contamination of the transmission fluid..

they noticed in the video the drivers seatbelt warning lamp illuminated.. this is because about 300 feet down the driveway you need to get out and open a gate.. neither my wife or I can honestly say whether or not this failure mode has happened when wearing the seatbelt.. GM says the car is breaking to a stop possibly because the driver isn't wearing their seatbelt.. really?

now Raymond you refer to the newer vehicles being intelligent? I find it unusual that the vehicle would be so intelligent that the people that built it don't even know what it's doing.. makes me think that I'm not driving a vehicle but a HAL 9000..



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post #7 of 14 (permalink) Old 12-13-2018, 12:57 PM
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Built in 'semi autonomous' safety features like this often do more harm than good, and it is a bit worrisome that the technicians scanner isn't even picking up on the parking brake being activated. I would be very surprised if this was traced back to the tranny fluid or something like having your seatbelt on. Sounds like typical deflection from the real problem.
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post #8 of 14 (permalink) Old 12-13-2018, 10:18 PM Thread Starter
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update time

so this morning off I go down the hill seatbelt on... and sure enough I come to a stop.. soooooo, the vehicle is still in drive, I set the park brake with the switch.. i release the park brake with the switch.. no joy.. I then take the shifter and pop it into neutral and off I go..

so now I go to the dealer so they can look at the trans fluid.. I explain how the park brake made no difference and how popping it into neutral allowed the vehicle to move again.. they look at the trans fluid and don't really see anything so I jump back into the car and off I go.. about 30 minutes later I get a call from the dealership saying GM is shipping a new transmission and transmission cooler.. they don't say if they found anything or not but GM decided to replace the transmission.. the interesting thing is they are told that when they install the new trans and cooler to service with fluid, run it for 5 minutes on the hoist and then drain and flush the trans and then service with new fluid.. this has me puzzled.. I don't know of any other system that could be contaminated by the trans so why the run, flush deal.. unless these new trans are creating contaminants in initial startup and then creating problems down the road so to speak.. so by running for 5 minutes and then flushing takes care of this issue.. the vehicle has 2K miles on it..

As an aside..
while I'm at the dealership there's another XT4 there that has been brought in on a flatbed after the transmission puked out all the fluid.. turns out a gasket was left out at assembly.. I haven't had a chance to look into who builds this 9 speed for GM and whether it's used on other vehicles yet, but I'm certainly going to look into that..

Bernie
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post #9 of 14 (permalink) Old 12-16-2018, 01:08 PM
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Replacing the transmission does seem a bit premature, but if its being done at no cost to you then so be it. It sounds to me more more like something software/electrical related but your dealer is obviously just going to start throwing new parts at the problem. And a gasket left out during assembly...oh no.
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post #10 of 14 (permalink) Old 12-16-2018, 08:07 PM Thread Starter
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I had a chance to talk to the shop foreman later that day.. asked him what GM technical was getting at re the trans fluid.. he said they were asked to pull a sample and determine if it was "cloudy".. he said they pulled a sample and said yes, it was cloudy.. that's when GM said they were shipping a new transmission and cooler.. GM obviously knows something is amiss but aren't saying anything..

Bernie
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