2017 Yukon Denali

[Blackcar]

Here is TSB on transmission might see if dealer will do TSB before purchase.

https://static.nhtsa.gov/odi/tsbs/2019/MC-10163890-9999.pdf

Here is extended warranty on A/C condenser.

https://static.nhtsa.gov/odi/tsbs/2020/MC-10178404-9999.pdf

On 2017 Denali there is extended warranty on Vacuum pump for brakes also.

 

[Jdlee2]

Here is TSB on transmission might see if dealer will do TSB before purchase.

https://static.nhtsa.gov/odi/tsbs/2019/MC-10163890-9999.pdf

Here is extended warranty on A/C condenser.

https://static.nhtsa.gov/odi/tsbs/2020/MC-10178404-9999.pdf

On 2017 Denali there is extended warranty on Vacuum pump for brakes also.

Awesome thank you for sending this.

 

[MobileHomie]

Could you further explain regarding the modification to the trans fluid t-stat? Thanks.

The guys on this forum call it "flip the pill". I have not seen a link or video of the procedure. It is turning something backward inside the t-stat, I think.
The Great Wise Ones at GM thought it was a good idea to put a thermostat in the transmission cooler lines. This prevents fluid from circulating to the radiator and gets the temp of the transmission up faster in the interest of improved fuel efficiency, allegedly. Without modifying the t-stat, even installing an aftermarket cooler won't help, cause the t-stat forces the temp up anyhow. Consequently the transmission fluid runs just a few degrees cooler than the temperature as the engine. Mine runs 175* unless I am pulling hills at 80 mph, then it's up to 190 pretty quick. Heat is the number one killer of auto transmissions.

 

[Jdlee2]

The guys on this forum call it "flip the pill". I have not seen a link or video of the procedure. It is turning something backward inside the t-stat, I think.
The Great Wise Ones at GM thought it was a good idea to put a thermostat in the transmission cooler lines. This prevents fluid from circulating to the radiator and gets the temp of the transmission up faster in the interest of improved fuel efficiency, allegedly. Without modifying the t-stat, even installing an aftermarket cooler won't help, cause the t-stat forces the temp up anyhow. Consequently the transmission fluid runs just a few degrees cooler than the temperature as the engine. Mine runs 175* unless I am pulling hills at 80 mph, then it's up to 190 pretty quick. Heat is the number one killer of auto transmissions.

Thanks for explaining more, very helping in understanding this more. Appreciate it.

 

[Blackcar]

I'm not positive but they reference problem with 8 spd as fluid getting moisture in it which the new fluid in TSB for 8spd the recommended fluid won't draw moisture which in my mind is why they want transmission at certain temperature to try and help with moisture situation,
I have no written prof of this but might be why they want trans to warm up to certain temp before opening thermostat on trans.

 

[RoadTrip]

I see a lot of the responses here focus on mechanical issues.

Let’s back up the electrical bus: So the polarity of the jumpers was reversed and so far the only telltale sign is a blown gauge cluster?

If the polarity is reversed on any modern car with a canbus network and several modules, any number of them could be damaged and/or glitch out at any time.

This vehicle could be a can of worms for you.

 

[Jdlee2]

I see a lot of the responses here focus on mechanical issues.

Let’s back up the electrical bus: So the polarity of the jumpers was reversed and so far the only telltale sign is a blown gauge cluster?

If the polarity is reversed on any modern car with a canbus network and several modules, any number of them could be damaged and/or glitch out at any time.

This vehicle could be a can of worms for you.

Yes you’re right about that. Have a refundable deposit on it while the dealer fixes it. Taking it to an independent mechanic before purchasing. I’m assuming the car would throw some codes if there was any residual damage still after repair?

 

[B-train]

In theory, yes electrical issues should show up right away if it let the smoke out of something, but that's not always the case. It may have weakened a component, but not killed it. Fortunately, most items are protected with fuses for overload, but not reverse power. I'm not sure if the ECMs have diodes to prevent damage for this scenario or not, but I would think GM anticipated something like this happening and put some safeguards in place.

I'd see if you can keep it for the weekend, have it inspected, and then drive it everywhere. Hit the freeway up to as fast as you normally go, do slow back roads, find some gravel roads with washboard bumps, etc. Give it a good test and shake down to see if any gremlins shown up. Actually........maybe do this first and then have it inspected, that way you can pass along anything you observe to the mechanic to look at.

As a side note, I bought the same year Denali from FL a few years back. Yours could be a real cream puff with that low of miles if there's no electrical gremlins from this.

I would follow the advice stated above plus some other additions:
1. Have them flush the trans before you buy it with the new fluid. I had the shudder issue caused by the fluid holding onto moisture. It was a ****** experience, but the new fluid has been perfect for over 100k now.
2. Shocks and struts should be fine, but as mentioned, it may be more of a dry-rot issue due to the heat and lack of use. Your mechanic can soap them up and look for cracks.
3. At the age you're at (not miles), I'd recommend new engine coolant. Service life is based off time, or miles, whichever comes first.
4. Engine lifters can't really be inspected, either they work, or make noise. I would recommend a RANGE Device, or custom tune to shut off AFM. I installed a RANGE in mine 110k miles ago and it's been great! Stick to 5k max for oil change intervals and you will have less likelihood of lifter issues - clean oil = happy sensitive parts.
5. The brake vacuum pump can fail on you. Ours failed at 45k. There is a new design in the TSB and I would push for it, or at least know what to expect when it needs to be replaced.

 

[Jdlee2]

In theory, yes electrical issues should show up right away if it let the smoke out of something, but that's not always the case. It may have weakened a component, but not killed it. Fortunately, most items are protected with fuses for overload, but not reverse power. I'm not sure if the ECMs have diodes to prevent damage for this scenario or not, but I would think GM anticipated something like this happening and put some safeguards in place.

I'd see if you can keep it for the weekend, have it inspected, and then drive it everywhere. Hit the freeway up to as fast as you normally go, do slow back roads, find some gravel roads with washboard bumps, etc. Give it a good test and shake down to see if any gremlins shown up. Actually........maybe do this first and then have it inspected, that way you can pass along anything you observe to the mechanic to look at.

As a side note, I bought the same year Denali from FL a few years back. Yours could be a real cream puff with that low of miles if there's no electrical gremlins from this.

I would follow the advice stated above plus some other additions:
1. Have them flush the trans before you buy it with the new fluid. I had the shudder issue caused by the fluid holding onto moisture. It was a ****** experience, but the new fluid has been perfect for over 100k now.
2. Shocks and struts should be fine, but as mentioned, it may be more of a dry-rot issue due to the heat and lack of use. Your mechanic can soap them up and look for cracks.
3. At the age you're at (not miles), I'd recommend new engine coolant. Service life is based off time, or miles, whichever comes first.
4. Engine lifters can't really be inspected, either they work, or make noise. I would recommend a RANGE Device, or custom tune to shut off AFM. I installed a RANGE in mine 110k miles ago and it's been great! Stick to 5k max for oil change intervals and you will have less likelihood of lifter issues - clean oil = happy sensitive parts.
5. The brake vacuum pump can fail on you. Ours failed at 45k. There is a new design in the TSB and I would push for it, or at least know what to expect when it needs to be replaced.

Thanks for the advice, this is all very helpful. Unfortunately we are out of town from this vehicle (2.5 hours) but will try to get a good test drive prior to.

I think I’m going to opt for a good comprehensive warranty as well to give me peace of mind.

 

[gjbfromplymouth]

Thanks for the heads up. Is this something that should be replaced every 25k or just the age of parts?

The air ride shocks need replacement about every 70,000 miles. Not sure if age is also an issue. Also see Technical Service Bulletin (TSB) 18-NA-355 for automatic transmission fluid replacement to eliminate shuddering and harsh shifting. It does not completely fix the problem but it helps.