2006 GP 3.8 Auto Transmission Issue ?

2006 GP 3.8 Auto Transmission Issue ? : 96,000 mi

When driving up a grade seems like a small slip, 200-400 jump in rpm's like it is trying to down shift then rpm's drop back down to where they were, depending on the length of the grade this may happen at intervals of 5-10 seconds or so, does not do this while on level grade or down grade, maintains speed up hill with cruise but with the rise and fall in rpm's, if the grade is a little steeper or up hill, rpms rise up 500-1000 then a downshift and everything seem to be fine, when there seems to be little load (cruising) and then a small increase in load (up grade) this happens.


This just started a few days ago, read on some other forums in older models could be a software issue saw nothing on the 2006

Concerned, Please Help,

Welcome to AF.

This is a common problem on any GM car equipped with a 4T65E autotransaxle. It sounds like the TCC locking and unlocking when it shouldn't. Did you get the 100K mile tranny service yet?

One of the main issues causing this symptom is a secondary ignition issue meaning spark plugs, wires, coils, etc. Have you done a basic tuneup?

Tranny serviced at 94,000, about a month ago, fluid changed and whatever else they do for $150.00

At first I thought it may have been a plug misfire, original iridium plugs looked good with some wear on the electrode, so I changed the plugs yesterday, runs smoother and got my mpg back to 28 + thought that may take care of the problem but I guess it didnt ,

So this may not be a trans issue at all?

Is this a serious issue that needs immediate attention?

Can I continue to drive this vehicle without damaging it?

Is this a trial and error fix or can it be accurately diagnosed / fixed?

What would you say the cost may be for a diag / fix on this issue?

I would appreciate any input,

Cant trust the dealerships until I have an good understanding of the problem so I can understand what they are trying to tell me they can do to fix it...

Tranny serviced at 94,000, about a month ago, fluid changed and whatever else they do for $150.00.

When it was serviced was it just a pan drop with ATF resupply and screen filter or a fluid exchange/flush? Did you have the "chuggle" before the tranny service?

BTW - The terms for this is either "chuggle" or "fishbite".

RE : When it was serviced was it just a pan drop with ATF resupply and screen filter or a fluid exchange/flush?

Not Sure, but I want to say it was the Exchange/Flush ??
I asked for the "Whatever is needed @100,000 mi transmission maintenance"


RE : Did you have the "chuggle" before the tranny service?

No , The "Chuggle" just started, Wed or Thurs of last week
Very slight , no noise, so shudder, no bang, shifts though the gears just fine.

Yeah it is not uncommon to have your first tranny issues after a service especially if it is classified as a flush which technically includes fluid exchange service. That is why we recommend a pan drop service only where the old ATF is drained, a new screen filter installed and new ATF.

You might consider getting it scanned and see if any DTCs are there stored in history. Some of the tranny DTCs do not trigger the SES/CEL light.

I'm really scared of the try this, try that, $1500 no fix.

Think I could pull the battery for a ECM code reset or is this more of a mechanical issue.

I'm a bit of a backyard mechanic myself, always worked on my own cars, built several big blocks in the 80's, but never ventured into the realm of automatic transmissions.

Maybe if I ignore it , it will just go away...

Just kidding

Thanks for your input.

ok, not to be a thread stealer or anything, but my GT does pretty much the same thing. like if I'm cruising down the highway and the car is in OD...if i try to speed up the car will chug then finally downshift.

i figured it was a bad TPS, but i wasnt getting an ses light or anything...so i just cleaned it and of course it didnt do anything.

i was gonna try and get the PCM flashed by the dealer since this transmission was rebuilt apx 6 months ago...and i figured that was the problem.

next time i have access to my dads OBDII scanner, im gonna check for codes, if there is a TCC code in there...does that mean the tranny has to be torn apart and have a new TCC put in...or is there some other kind of fix? :confused:

oh yeah...car is a 1998 GP GT w/ a hair over 79K on it.

This is by no means the correct way to fix this issue but unhook the negative battery terminal for an hour or so. We have had 2 cars in the shop like this and could not find ANYTHING wrong. These cars have not been back in 6+ months with the described issue. Our tech line has had a very high % of luck with this too. Also check all grounds and clean if needed.

Had the car scanned, No codes present ...

Persuaded a GM tech to take it for a drive, we drove around for 10 min or so, issue showed itself 27 times, his answer was "Hmmmmmm, schedule an appt and we'll do some diags".

Lots of internet research, information overload,,,

Picked up a bottle of Lubegard Red Friday eve, Saturday morning drove the car around for a while to get the tranny temp up, RPM bounce / TCC lock Issue still there, So here goes the Lubegard, label says 1 oz per qt at idle in park, So I added 8 oz, checked fluid level it was ok, so I added the rest of the 10 oz bottle and took the drivers seat, Very skeptical of a fix, heart beating in fear of the $2500+ repair, drove around for a while, back roads, highway, all rpm ranges, all gears, manual and auto, cruise control from 25mph up through 80mph+ "I Could Not Reproduce The Problem" Kept driving around, Issue Is Gone, 2 hrs and a 100 miles later I'm sitting in my driveway, contemplating,,, Is it really gone ? Whether this is long term or only temporary remains to be seen , but as for now I'm doing the happy dance and my blood pressure is back to normal. Thanks for everyones input

Interesting info...in my thinking this hints at some sort of shift solenoid which is unresponsive, or internally dirty.

I had similar problems with a chuggle between 1-2 shift on a 2001 Trailblazer which was amplified when the fluid warmed up when making a "soft" shift (IOW not a wide-open-throttle drag launch). I traded the vehicle before finding out what was really wrong but I was contemplating changing the 1-2 shift solenoid.

Interesting info...in my thinking this hints at some sort of shift solenoid which is unresponsive, or internally dirty.

I had similar problems with a chuggle between 1-2 shift on a 2001 Trailblazer which was amplified when the fluid warmed up when making a "soft" shift (IOW not a wide-open-throttle drag launch).

Interesting thinking but speculation at best and obviously you did not resolve the issue with your Trailblazer which doesn't use a 4T65E autotransaxle so I do not see the relevancy.

If it was the 1-2 shift solenoid you think that would cause these symptoms? I don't. :grinno: And most likely a tranny DTC would set. A bad 1-2 shift solenoid would clearly affect automatic shifting and other gears but the OP stated no such issue with shifting. If the 1-2 shift solenoid was really bad you would lose other gears.

The reason is the 1-2 and 2-3 shift solenoids form a matrix and work with each other depending on the commands from the PCM module. For example in 1st gear both the 1-2 and 2-3 shift solenoids are energized (on). In 2nd 1-2 is off and 2-3 is on. 3rd both 1-2 and 2-3 are off. In 4th 1-2 is on and 2-3 is off.

The reason is the 1-2 and 2-3 shift solenoids form a matrix and work with each other depending on the commands from the PCM module. For example in 1st gear both the 1-2 and 2-3 shift solenoids are energized (on). In 2nd 1-2 is off and 2-3 is on. 3rd both 1-2 and 2-3 are off. In 4th 1-2 is on and 2-3 is off.

I do agree completely with this, but note from your quote above what actuator changes states during the 1st-2nd gearshift...it is the 1-2 solenoid, which is why I logically picked that as a potential place to start component replacement.

My experience with the SES-trans codes is that the shift solenoid has to "go down for the count" where it can't even change state before a code will set. The "small" problems don't induce a SES-trans code, and my guess is that GM's call on this was to keep the "filter medium" rather "dense" on what to allow to cause a SES-trans code.

Arent some trans "chuggles" caused by leaky valve body gaskets?

Just curious.