Update: 99 Yukon NP8 codes 1-2 shift scan tool?

[the 18th letter]

Is this scan tool really 1100 bucks? I'm not sure I can justify that when I cant do much more than change oil what's the most economical for the least mechanical mechanic.

 

[Smooth_Rider]

If a scanner isn’t in the immediate future, I’d try dropping by a tire shop or similar chain-store type place and ask the guy if they’d pull the codes for you real quick.

You might also consider getting a copy of the GM service manual. It has the diagnostic procedure tables associated with each code (once you get them) and are pretty straightforward. It’s largely written around the Tech2 scanner and can include references to special ($) Kent Moore tools, but it’s certainly worth looking into as you can usually workaround those things.

I don’t think that they have them for 1999, but the site below does have free PDF copies for 1998. While that should suffice for the majority of things on the truck, I couldn’t speak to any differences in the 4l60e for those two years. Best look for a 99 manual if you’re getting into the weeds on a transmission.

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

Alldatadiy.com is a subscription service which has nearly verbatim copies of the GM manual and is pretty easy to use. Used paper manuals (eBay) are another option.

Good luck!

Edit: Here are some sample pages from the 98 manual…

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Thanks east, this is helpful- these sample pages are my kind of deal (way of thinking/working through things). Like others on here are saying and I knew would all-too-soon be the case, I broke down and ordered a Launch bidirectional scan tool today (so much conflicting info on Autel models, verions, etc I caved on it).

I will for sure download the manual on that link for my 98 Tahoe!

 

[Smooth_Rider]

If you are going to any more than put gas in and check the oil you should own a scan tool and a digital multi meter just for starters. The Autel is a good one for basics and very reasonably priced.
If I was a guessing man the first guess for the T case would be the switch on the dash, they are a common failure.
I always like the references to a not a modern/computer car deal. Kind of limits you to over 40yo vehicles.

Fair enough, but as a matter of fact, I have done a lot of maintenance and repairs on two gmt400s (I have a very cheap scan tool but its limited abilities haven't come in useful) and haven't needed a fancy scanner until now (and I did just order one). I may be an old dog learning new plastic computer car tricks, but if the apocalypse comes (or a really good EMP) guys like me can get and keep old cars running with a matchbook, bailing wire, chewing gum and a handful of tools while these plastic throw away cars are dead. I wonder how many young mechanics learn any of the old stuff? How to diagnose the old ways? How to tune or rebuild a carburetor? Road time a distributor? What the hell is dwell? Lol...
Thanks for the tip on the dash switch- I swapped it out with the one in my Tahoe and it works in the Tahoe, Tahoe switch same (nothing) in Yukon, so that was eliminated today.

One thing I keep coming back to is this 1-2 shifting issue generally improves as temps increase. So that could be Trans/Tcase fluid temp and/OR ambient temps in and about the truck/engine bay/undercarriage increasing enough to effect the functionality of a sensor, switch, or computer...ah all knowing magical scan tool where art thou?

 

[Eman85]

When it comes to old trucks like the 91-99 models a good used Snap-On "brick" or a Tech II can't be beat. Don't need a whiz bang newer scan tool on this stuff.
As for the apocalypse I've been through Y2K and all of the tin foil people waiting for all of the computer cars to die so they could show off with their 7mpg smoker.
91-99 is primitive sys terms in comparison to anything made in the late 2000's forget about in the 2020's. I can set points with the best of them. Owned plenty of daily drivers with points, glad those days are over.

 

[dmhscorpio]

Hoping someone can send me in the right direction. My 99 4wd Yukon had two previous owners. Original owner was OCD on maintenance, put 130k on it, second owner was good on maintenance, but harder on truck, put 70k. I bought at 200k, and been "fixing" since. Now at 202k. I'm an old gear head and do most work myself, but not a modern/computer car savy guy. I did a trans service on her about 1k ago and was pleased with the lack of gunk in the pan and a relatively clean magnet. Prior service 30k back. At this point the biggest issue was the dash is gone/rotten and shakes to hell over potholes, and the front end is shot- everything was worn out. Including axle boots, CA bushings, tie rods, just all of it.

So before I get to installing this pile of new front end parts, the truck starts shifting strange. Mostly just when its cold, and mostly just 1-2 shift. Like its short shifting into second...lugging and almost stalling out. I can manually shift it and it's ok. After it warms up, it shift better, but still not perfectly correct. So I'm thinking wtf, did I mess something up with the service I did? At some point the CEL came on and off, the "service 4wd" light came on and off a few times then stayed on.

I took the truck to a local/reputable trans shop and they came back with "its not your transmission, it has to do with the Tcase" they said they had "multiple codes" but that's where the $125/hr diagnostic charge starts.

One thing I should add here is that after the shifting issue started, but before any dash lights (and before I took it to the transmission shop) the trucks alarm system, that was dealer installed when the truck was sold new, went haywire, going off in my driveway with no way to shut if off than to disconnect the battery. Leaving the batt disconnected for a few days didn't help/reset anything. I couldn't start the yukon or turn the alarm off. So I cut the siren, and "uninstalled" the guts of the whole thing. Ever since then, seemingly randomly, I can hear a relay clicking under the dash, which I correlate to the alarm removal. I don't have any idea what caused the alarm system to freak out initially, or if it has had any other impact on anything.

In my semi ignorant run up to addressing this, and because I have another identical truck, and because they were relatively cheap, I acquired the following parts with this problem in mind: TPS, VSS, 4 button 4wd selector, Sonnex 1-2 pinless accumulator kit.
My gut says this is a sensor/computer issue.

So, before I blindly throw money I dont have at the transmission shop, here are my thoughts and questions- since the shop wont volunteer the codes, would a second opinion be in order? Would ANY shop volunteer the codes? Can anyone recommend an affordable/easy to use scan tool capable of reading transfer case codes? I also assume from my rudimentary understanding of this tcase that it can't be bypassed or "unmarried" from the trans as older units can. Any other solutions, thoughts, ideas?

I use this to analyze my 99 Tahoe 2 door 4X4. https://www.vxdiagshop.com/wholesale/vxdiag-vcx-nano-for-gm-opel.html I can look at anything a Tech2 can. I haven't changed anything other than the tire size with it, but will soon. It is $45 for 2 years per vehicle from GM for the SW code to do so. Ignore all the negative info on the installation of the VXdiag. I used a windows 10 and the supplier USB dongle. It worked the first try.

 

[Smooth_Rider]

I use this to analyze my 99 Tahoe 2 door 4X4. https://www.vxdiagshop.com/wholesale/vxdiag-vcx-nano-for-gm-opel.html I can look at anything a Tech2 can. I haven't changed anything other than the tire size with it, but will soon. It is $45 for 2 years per vehicle from GM for the SW code to do so. Ignore all the negative info on the installation of the VXdiag. I used a windows 10 and the supplier USB dongle. It worked the first try.

Thank you! That looks VERY interesting, and $45 is reasonable two years of updates, even if its just one vehicleI guess.

but...I just ordered this:

2023 LAUNCH X431 Fit for GM Bi-Directional Scan Tool, All Reset Full System Diagnostic Scanner, AUTOVIN,ECU Coding,Battery Register,Key Programing for Buick/Chevrolet/Cadillac/GMC,Lifetime Free Update https://a.co/d/ffxI9sV

For about the same price that supposedly has free updates. I watched some YT videos of it, seems legit, cheap enough for a first "real" scanner to learn with hopefully.

 

[89Suburban]

Thank you! That looks VERY interesting, and $45 is reasonable two years of updates, even if its just one vehicleI guess.

but...I just ordered this:

2023 LAUNCH X431 Fit for GM Bi-Directional Scan Tool, All Reset Full System Diagnostic Scanner, AUTOVIN,ECU Coding,Battery Register,Key Programing for Buick/Chevrolet/Cadillac/GMC,Lifetime Free Update https://a.co/d/ffxI9sV

For about the same price that supposedly has free updates. I watched some YT videos of it, seems legit, cheap enough for a first "real" scanner to learn with hopefully.

Please let us know how it works out for you. Does it do idle relearn?

 

[Smooth_Rider]

Please let us know how it works out for you. Does it do idle relearn?

From reviews I read it does. The main complaint was the menus didnt always seem logical- like you have to memorize them or make a cheat sheet on where to find stuff.

 

[waveryd]

I would strongly consider the transfer case encoder ring. When mine failed my symptoms were almost identical to what you have described. This failure did not produce any dtc's. It is not expensive or difficult to change. Just a thought.

 

[Smooth_Rider]

Please let us know how it works out for you. Does it do idle relearn?

From reviews I read it does. The main complaint was the menus didnt always seem logical- like you have to memorize them or make a cheat sheet on where to find stuff.