Wierd shift

[Tatman48]

Hey all, new to site and yukons, but not new to forums. I bought this 08 Yukon Denali 6.2 a few months back. Tgis things shifts all over the place. I am getting rough downshifts to pass, and sometimes quick shidts between 2 then 3 to 4 quickly on an easy peddle. I have no codes on computer so I am leaning towards the peddle position sensor. Unless you can have a bad tps and no codes, also my manual up and down does nothing when in manual. Any help would be awesome.... I had in wrong forum...

 

[kbuskill]

Hey all, new to site and yukons, but not new to forums. I bought this 08 Yukon Denali 6.2 a few months back. Tgis things shifts all over the place. I am getting rough downshifts to pass, and sometimes quick shidts between 2 then 3 to 4 quickly on an easy peddle. I have no codes on computer so I am leaning towards the peddle position sensor. Unless you can have a bad tps and no codes, also my manual up and down does nothing when in manual. Any help would be awesome.... I had in wrong forum...

You need a Tech2 or similar device that can communicate with the TCM to see if there are any internal codes.

 

[Doubeleive]

you might check your MAF sensor, try cleaning it and see if it make any difference, the spray is like $3 at almost any autoparts store, if the maf is goofy it can cause all kinds of weird stuff with idle/acceleration & shifting. just my .02

 

[Tatman48]

You need a Tech2 or similar device that can communicate with the TCM to see if there are any internal codes.

Ok

 

[the_tool_man]

you might check your MAF sensor, try cleaning it and see if it make any difference, the spray is like $3 at almost any autoparts store, if the maf is goofy it can cause all kinds of weird stuff with idle/acceleration & shifting. just my .02

I'm having similar issues. Since the truck is new to me (2012 Yukon 99k miles), I don't know if it's normal or not. I've already started feeding it Lucas injector cleaner, and ordered a full complement of Amsoil fluids. I'll try cleaning the MAF and see if it makes a difference.

You need a Tech2 or similar device that can communicate with the TCM to see if there are any internal codes.

Got any specific recommendations on a scanner? I've read only a little. But it looks like "real" ones are expensive ~$1500, and require software updates and a subscription to a GM database to work properly. If that's true, I'll just take it to someone and pay them to scan it.

 

[kbuskill]

I'm having similar issues. Since the truck is new to me (2012 Yukon 99k miles), I don't know if it's normal or not. I've already started feeding it Lucas injector cleaner, and ordered a full complement of Amsoil fluids. I'll try cleaning the MAF and see if it makes a difference.



Got any specific recommendations on a scanner? I've read only a little. But it looks like "real" ones are expensive ~$1500, and require software updates and a subscription to a GM database to work properly. If that's true, I'll just take it to someone and pay them to scan it.

The "knock-off" Tech2 scanners can be had for around $300 now. Lots of guys on here have them and they seem to work great.

 

[Tatman48]

I need to get 1...

 

[iamdub]

+1 on cleaning the MAF and having the TCM scanned. Cleaning the MAF may improve the shifting and maybe even the fuel economy. I don't see it fixing the manual shifting unless this is disabled when the TCM has fault codes.

Even when operating as it should, the stock trans tables in these things SUCKS. They wanna get to top gear as quickly as possible, causing lugging, then they have to downshift cuz you're giving it more throttle, then they upshift again... A good tune makes a world of difference and can even extend the life of the trans because it's not shifting nearly as much. My ex-work van was a 2013 Express with a 6.0/6L80 and I manually shifted it it's entire life. When most other techs were needing new transmissions at 75K-150K miles, mine went 230K miles and was a champ 'til the last mile. If I had changed the fluid, it might still be alive. But, it died with the same fluid it left the GM assembly line with.

 

[Tatman48]

+1 on cleaning the MAF and having the TCM scanned. Cleaning the MAF may improve the shifting and maybe even the fuel economy. I don't see it fixing the manual shifting unless this is disabled when the TCM has fault codes.

Even when operating as it should, the stock trans tables in these things SUCKS. They wanna get to top gear as quickly as possible, causing lugging, then they have to downshift cuz you're giving it more throttle, then they upshift again... A good tune makes a world of difference and can even extend the life of the trans because it's not shifting nearly as much. My ex-work van was a 2013 Express with a 6.0/6L80 and I manually shifted it it's entire life. When most other techs were needing new transmissions at 75K-150K miles, mine went 230K miles and was a champ 'til the last mile. If I had changed the fluid, it might still be alive. But, it died with the same fluid it left the GM assembly line with.

Cool, since I just bought it. I want to do a trans filter and flush... But it has 150k. Can they change fluid,out without flushing a cleaner through? I dont want to cause more issues

 

[iamdub]

Cool, since I just bought it. I want to do a trans filter and flush... But it has 150k. Can they change fluid,out without flushing a cleaner through? I dont want to cause more issues

I didn't know anyone ever ran cleaners through transmissions. I know many DIY'ers at home just drop the pan to change the filter and refill whatever fluid was lost with that. But there's still all that old fluid elsewhere in the trans and torque converter so dropping the pan only replaces about half.

I've seen shops use machines that basically refill the trans with new fluid as the old stuff is pumped out. Maybe this is what the call a "flush". Not sure if any run a cleaner during this process.

I pop off the hose that the fluid takes from the cooler back to the trans and have it drain into a large pan. With the engine running and trans in
"Neutral", I pour new fluid into the dipstick/fill tube (using a funnel) as the old fluid is pumped out. I continue this until the fluid coming out is the same color as the fluid going in, then continue for a quart or so to make sure. Then I change the filter, draining the trans pan into a clean pan and being careful to save as much as possible to re-use, then top off the fluid. I wouldn't consider this an aggressive "power flush". It's just a total fluid replacement.