Let him confirm or deny, why bother speculating? Waste of time and energy. Three pages and no positive determimation of what transmission is installed. OP likely went to sleep, ill check the thread again tomorrow sometime...
RPM Fluctuation
- Thread starter RobbyD
- Start date
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Yes, sorry gentleman. Had to hit the sack early last night and was up early this morning on an 8 hour road trip. This is my first time back on the computer. It is indeed a 4L60E.
Thanks for hopping in trying to help.
Did you take your Tahoe on this road trip? If so, any change to the symptoms? Any new issues pop up since you last posted?
Read through the thread and many are pointing to the TCC, which is certainly within the realm of possibility...First thing I'd do (and many others have already mentioned, so won't be news to you) is stick a bi-directional scan tool on the vehicle, scan for DTCs (particularly anything related to the transmission) and drive it on surface streets and the freeway...Have all live transmission, torque converter and engine data streams displayed...Make sure your TPS, MAF cam, crank position and other sensor readings are consistent with both reference ranges and/or reality (i.e. your TPS pct should be consistent with throttle input at any given time) - If the TPS is reading too strong, PCM may be unlocking the TCC when it shouldn't be doing so, for example. Also make sure no issues w/break light switch, etc as if the breaks are tapped, TCC unlocks.
Assuming nothing is amiss with your engine management system (no DTCs for anything, etc), ABS electrical circuits/sensors, next look at ISS data (if you have an input speed sensor - they started appearing in 4L60Es for the late 2006 model year in some vehicles and proliferated across all 4L60Es throughout 2007/2008) and TCC slip speed - should not be more than 5mph or so when cruising steadily in lock up...If it is, then TCC is slipping...Let's assume that is the case, scan tool shows major TCC RPM slip - what's next? Have to find out why...
Lead suspects are as follows:
- Worn/failing/damaged TCC (converter going bad)
- Worn/failing/damaged TCC lock up solenoid (was wiring harness and TCC solenoid assembly replaced during the last overhaul?)
- Failing TCC PWM Solenoid (not likely, you'd be in limp if this failed electrically, but can fail mechanically and not throw codes or result in limp mode)
- Worn TCC regulator valve (P1870 or P0894 DTCs) in the valve body - Was this valve updated during the overhaul? Do you have VVT/ACM - if so, PWM cannot be mechanically deleted
- Worn TCC Control valve in the pump - Perhaps install the Sonnax 4L60E drop-in HP TCC Control valve as a precautionary measure (note - if you have an ISS this won't be possible without taking the trans out, removing the pump then removing the input speed sensor)
- Worn pump stator bushings (possible; more likely if the bushings were not replaced during overhaul)
- Worn 3-4 clutch pack
- Leaking 3rd accumulator check ball capsule (not likely but if it's leaking, will degrade the 3-4 apply circuit, creating a domino effect that ultimately leads to 'out of schedule' TCC unlock
- Worn pump (excessive clearance between rotor/slide and deck) - was the pump remanufactured during overhaul?
- External wiring harness wear/short-to-grounds/etc (unlikely but possible)
- PCM failure (rare)
Once you confirm on the scan tool that you have TCC slippage, then the next step is to drop the pan, pull the VB assembly and internal transmission harness/TCC lock up solenoid, test both for defects. While I have not personally seen or heard a weak AFL circuit causing only TCC symptoms like those you're experiencing, it's possible...If the AFL valve is worn, then available hydraulic apply pressure available to all the solenoids is less - this can be compensated for with the installation of a corrective shift kit or replacement drop-in AFL valve (Sonnax also makes an oversized one but it requires special reamers and fixtures for installation). The TCC regulator valve can simply be fixed with an updated Fitzall valve unless you have VVT/AFM.
If the causes are inside the case, trans has to come out for overhaul.
My initial .02c
Let me know if you have done any or all of the above or if you have any additional questions and I'll respond as soon as I can.
You're a saint. You've given me some work to do. Very busy at work the next couple of days. I will doing all my testing on Thursday or Friday. I will report back with my findings and any images I might be able to provide. I will be checking back in on this thread in between though. Expect to hear from me Friday night the latest with what I've come up with.
Seriously can't thank you enough for typing all that out for me. I won't let the information go to waste. Wish me luck!
Sorry for the delay gentlemen. I only got around to doing the road trip part of the suggestions this weekend. I'm including a link to a video of 5 minutes of autel data I recorded. Sorry if it's a little sloppy. I didn't want to take the camera off the autel so that we could see everything that was happening, should be able to hear what's going on with the RPMs with volume. I do scroll through all the trans data throughout the video so you can see different parameters.
From what I've found, it does seem like my TCC speeds are all out of whack, but please do correct me if I'm wrong. Everything else was in check as far as throttle postion, intake position, brake actuation, etc.
There were no trans codes being thrown and nothing stored in history. I have access to the autel as well as tech 2 so if there's anything else I need to look for on those please advise. I'm pretty good with doing my own service on my vehicles. This would be my first time going into the trans myself. If/when I do it myself, if you guys have any suggestions to video walkthroughs, they would really help me along the way.
I understand I might be at the end of the road here as to what I can do with a scan tool and I think it's time to get my hands dirty.
Side note that I should've mentioned earlier. I did have an engine tune on the truck to deactivate AFM. I removed that tune as of recording the video and AFM was back on. Nothing changed as far as different, better, or worse symptoms.
Sorry again for the delay. I have a bit more free time this week so I should be more on top of things.
https://vimeo.com/manage/videos/910113561
Here's a screenshot of the relevant information...Notice the duty cycle is over 90% when TPS angle is less than 25% and the TCC circuit is enabled WHILE slip speed is greater than 0-5 RPM...90%+ duty cycle means the PCM is commanding a full charge of max available line pressure to the torque converter clutch and it's still slipping. Slip speed under these circumstances should be zero.
Now the question is: Why is the TCC slipping?
See my above list of suspects and start testing each, ruling in and out as you go...
Oh boy okay. I'm not mechanically inclined enough to pull a whole trans out, so it seems like there's only a few things I can do/check by only pulling the pan. From your previous post, these seem like the things I can do: "pull the VB assembly and internal transmission harness/TCC lock up solenoid, test both for defects"
You can actually do some DVOM testing w/your multimeter with the pan still on, but may require some contortionist work on your part to get to the transmission connector on the pass side of the case. But if you're able to, here's a diagram showing all the pin locations where you can confirm/deny continuity for all of your solenoids, including the PWM and TCC Enable (lock up) solenoids. But it may be a lot easier to simply drop the pan for this exercise.
I'll be doing some 4L60E videos over the next several days, posting them to my Youtube channel so if you're not a subscriber yet, please sub so you can be notified. One of the videos will cover addressing P1870 and the torque converter clutch regulator and lock up circuit, which is a source of many TCC-related drivability symptoms.
I'll definitely be looking forward to those videos. I have a buddy who's a little bit more savvy with trans related work. Going to see if I can't get him to help me out sometime this week. This gives me a good direction to follow though. Again, I really appreciate the guidance. I'll be posting updates as I find them.
Sounds good, man. Let us know if you have any more questions or run into any problems.
