Jump to content

Transmission Shifting Hard

JJHYukon

Recommended Posts

JJHYukon New Member

JJHYukon

Posted
Posted

I have noticed that my Yukon has been shifting really hard. I can drive around town all day and it will shift fine. I only notice it shifting hard when i stop and take off after i have been driving on the highway at a high speed. But if i turn off the vehicle for a few seconds it won't shift hard anymore. I just can't figure it out. I just put a transmission filter in it and it does the same thing. It almost has to be something electrical because i can shut it off for a few seconds then it shifts normal again. If you have any idea of the problem let me know.

Thanks Justin

 

 

97 GMC Yukon

 

My Webpage

GM-Tech Senior Enthusiast

GM-Tech

Posted
Posted

Your truck almost certainly has a DTC P1870 in it. This is a slip code, but not the kind of slip you are probably thinking. This will not necessarily turn the MIL on.

 

What it is is that at highway speeds, the torque converter is not maintaing full engagement and the PCM sees what's called a high "slip speed". When the TCC is on, input speed vs. output speed of the trans is compared and the PCM can tell if there's slippage, like would be the case if the TCC was not on. If slip speed is not nearly zero for a certain amount of time and under certain conditions, the PCM sets a P1870. This usually only happens on a highway drive where the conditions occur that would make this problem apparent to the PCM.

 

When this DTC sets, the results is that the PCM commands full line pressure to the trans in an attempt to prevent damage, which you don't notice until you come to a stop and then pull away and it makes it's first shift, which is usually neck snapping hard.

 

Cycling the key off will clear this problem, though not the DTC. A valve body problem is possible. Pretty common actually. But we also had some input shaft bushing problems back then too. You didn't see any brass looking material in the pan when you changed the filter, did you? If so, that's the bushing.

JJHYukon New Member

JJHYukon

Posted
  • Author
Posted

Yes it is throwing a p1870 code. I didn't change the filter myself so i don't know if their was any brass in the bottom of the pan. If i took it to a local Aamco Transmission Shop could they fix the problem or would i be better off taking it to the dealer.

GM-Tech Senior Enthusiast

GM-Tech

Posted
Posted
If i took it to a local Aamco Transmission Shop could they fix the problem or would i be better off taking it to the dealer.

 

I would hope a dealer would do a better job, but it really depends on the person diagnosing and fixing the vehicle. You'll definitely pay more at a dealer.

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.

  • Forum Statistics

    250.3k
    Total Topics
    2.7m
    Total Posts

  • Member Statistics

    342,725
    Total Members
    8,960
    Most Online
    Griffin Donovan
    Newest Member
    Griffin Donovan
    Joined

  • Who's Online   4 Members, 1 Anonymous, 768 Guests (See full list)

  • Latest Articles

  • Posts

    • davester
      Anyone had to replace their Onstar module a.k.a. Telematics unit?

      By davester · Posted

      Hasn't come up in the 3 gm forums I follow. And only gm knows the frequency of failure of that part. LMG, you want a recall so it's replaced for free...
    • newdude
      Transmission Woes :-(

      By newdude · Posted

      You need a better code reader/scanner.  You are missing codes.  Did the dealer give you a copy of the SAVI scan from that visit?     If the fluid hasn't been changed, change it.  Shudder will likely go away.  
    • newdude
      Can anyone decode a VIN to determine if this truck has had emissions issues or a recall?

      By newdude · Posted

      TLDR to my other post...   Hard. Pass.  Too many what ifs.     Are you set on a 3.0 Duramax?  Have you considered anything not GM just in case?  If you don't have to have a pickup, lots of other options for $27,000 out there.   
    • newdude
      Can anyone decode a VIN to determine if this truck has had emissions issues or a recall?

      By newdude · Posted

      I see some red flags.   - No mention in the Carfax if the oil pump belt was changed.  LM2s had a 150,000mi service interval, and its got 164,245mi on it.  So right out the gate it needs about $3000-3500 for that to be done before driving it another 150,000mi.  Belt is at the rear of the engine.     - If something happens to the transmission valve body, the special coverage is expired by mileage.  That will likely be an out of pocket expense, with zero or near zero GM participation if something happened even though its in by time.   - 2020 LM2s seem to need timing chains after 80,000mi at some point.  They fixed this end of 2020/starting 2021 model year engines.  They will usually set a P0016 I think?  There is another $8000-10,000 if it needs a chain.  The main chain is at the back, secondary at the front so the pump belt would be done at the same time if it needed chains.     - Long oil change intervals.  7,000-8,000mi on average, probably close to 0% or perhaps to or beyond 0% on the OLM.  Lots of them not at the dealer which makes me wonder how much of the oil ran through that truck was the proper Dexos D rated 0w20 oil and not just gas engine 0w20, which is not the same at all.     - Long fuel filter changes, again likely taking the fuel filter life to 0% or more.  First one went 28,603, second was done 43,094 miles later at 71,697, from there another 46,452mi to 118,149mi, and then the most recent one 37,026mi later at 155,175mi.  So counting its original fuel filter, its had only 4 fuel filters on it.  No bueno IMO.         Good news?    - It has had only two warranty trips to the dealer.  The first free service (end of December 2020 on the Carfax), and the transmission reprogram recall (end of August 2025 on the Carfax).     - Truck did a LOT of moving, so that might explain the lack of emissions related repairs like bad NOX sensors, bad exhaust temp sensors, bad glow plugs, etc.         The "emissions system checked" could just be how something was flagged for Carfax.  GM dealers have to do SAVI reports for warranty repair orders so they scan the truck.  So its possible that is there for that?  
    • cherryred21duramax
      Can anyone decode a VIN to determine if this truck has had emissions issues or a recall?

      By cherryred21duramax · Posted

      Thank you, @Z45!   NOTE - No all repair shop/Dealers reports to Carfax   That is my main concern.  The CARFAX looks way too clean for a 6 year old anything with 164,245 miles.  Even something known for reliability (like many Toyotas) typically has a lot more replaced, like a Nav screen, interior trim, shock/strut, or brake pads.  And surely the last set of tires (installed at ~58k miles) would be bald unless those were all highway miles.   I'm tempted to pay a local dealer to look up the VIN, but am not sure if that will be worthwhile.  Last time I did this, it was 100% useless, and I felt scammed - they noted the bumper was replaced years ago and that's it.  A 5-year old could spot the accident damage, even though nothing was on the CARFAX.   After giving the dealer a call, the truck may have a hard shift, but they have to verify with their mechanic if that's even a concern.  And I've test driven about a dozen of these now, many near Chicago, and half the trucks shift hard/odd at all throttle positions.  The ones with aftermarket lifts/larger tires shift terrible, and 3 stock trucks shifted so violently I thought the transmission valve body was going out.   At this point I'm conflicted, as I need a vehicle, and am coming up short locally.  Northern trucks in this price range tend to have either multiple owners, a lot of mods (lifts/oversized tires without re-gearing), and are generally in rougher shape.   If this truck showed up in your neighborhood for $27k and you had to purchase it sight-unseen, with the possibility of needing a 10L80 rebuild, torque converter, or rear end - would you do it?  I'm convinced most of the 10L80 trucks I test drove are broken, they can't all shift so bad, with massive flares/slipping/lurching and mis-matched downshifts like a teen driver learning stick.

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...