Tranny issue with possible connection to throttle body?

[dhanger]

Greetings, first post not counting my intro post.

2004 TB LS, all original stock. 190K miles on original 4.2 and tranny. All miles in Arizona heat!

So recently I started having slippage in 2-3 shift, not much more to say about that but only matches #30 on this list:

4L60E list of failures and causes

While researching for a particular failure for @trailblazer075 , found this over at LS1Tech (who copied from GMT400.com). Could be useful when trying to find a cause for a particular failure and diagnosis...

gmtnation.com

No other symptoms that I can feel or hear. There are no DTC's at the moment.

I'm mostly original owner (bought at 12K miles) and I've been pretty meticulous about routine maintenance, although I've been hard pressed to be sure of the last tranny service, according to my records the last service was 8 years ago but I think I must have lost a record or 2 along the way. I know I've done it myself more than a couple times and had shop do it a few times as well.

So a couple weeks ago I took it in for diagnostic, the tech took it for a drive with a scanner. When he returned he told me that he could tell what I was talking about but he showed me something on the scanner related to the throttle body and he recommended taking care of that before going any further. I didn't pay close attention so I'm not sure what the scanner was telling him but I had been having some issues with the throttle body (maybe more accurate to say 'at' the throttle body as the problem could be other things) so I figured I needed to tackle that first. I tried to get some answers from 'the other place' but got nowhere with that, you can read my original post to get all the details:

Throttle Body malfunction

Greetings- 2004 TB LS 4.2 L6 engine 190K miles Issue: engine shuts off suddenly on random occasions as if the key is turned off, starts up easily right after and problem does not return for some time. Can go weeks in between occurrences. I've spent hours and hours reading dozens of posts...

www.trailvoy.com

Something else maybe related, maybe not. About the same time that I started noticing the slippage I also started noticing some unusual noise, especially with the window open and the sound bouncing off walls and buildings. At first I thought it might be an exhaust leak but all's good there. The sound is noticeable only on acceleration, nothing on cruising or coasting, that was another reason I suspected exhaust leak.

Question 1: is there good reason to investigate the throttle body before tackling the tranny, or should I just tell them to go ahead with a rebuild? I'm planning on a road trip in June and I don't want to get stranded while out of town.

Question 2: is it likely that the sound I'm hearing is related to the tranny or should I continue looking for something else? Could be metal resonating somewhere, not banging intermittently but smooth and consistent throughout acceleration.

Thanks,
Dan

 

[Mooseman]

At 190k, you did good with it and it owes you nothing. As a comparison, mine failed at 320k km (199k miles) but was a sunshell failure.

For the throttle body, if it would have failed, there would be a DTC and likely go into limp mode. I can't see what a throttle body issue would cause issues with the tranny shifting except if it goes into limp mode. The only non-failure problem with them is if it's dirty it will cause idling problems. You could clean it as per this thread:
How to clean your throttle body
The only relearn procedure for the TB is to disconnect the battery while cleaning it. In fact, it has to be cleaned any time the battery is disconnected.

And there's this thread regarding throttle body problems:
I-6 Throttle body questions (Failure)

You could try a pan drop and fluid flush/exchange but when it starts slipping like that, it's usually rebuild time. If you were to boost the pressure or put an additive, it may fix it temporarily but it would eventually fail completely.

Maybe others can chime in with their thoughts?

 

[dhanger]

Hi Mooseman-

So you're of the opinion that anything throttle body related would probably not have any effect on the tranny? I still remember years ago when trannies had vacuum modulators and shifting was partly controlled by manifold vacuum, which was obviously controlled by throttle positioning. I know things aren't that way on this model (I don't think) but still there must be some kind of input/feedback with respect to the throttle and shifting. That's clear to me when I let off the throttle for the 2-3 shift it helps smooth it out. Not arguing, just trying to have better understanding--I don't want to push a rebuilder into doing something they aren't comfortable with but on the other hand I'm not sure I can have confidence in their abilities.

I myself don't really see a connection but I don't have any way of knowing. If you had time to read my other thread you'll know that this throttle body issue I've had has been going on for ~10 years while the tranny slipping is a recent issue. I've tried several things for the throttle body (including cleaning several times) but still haven't found a cure for it.

I have considered your suggestion to change fluid/filter just in case the filter is clogged at this point (if I truly have neglected it for 8 years) but since I have no other symptoms beside the 2-3 slippage I have doubts that would fix anything, and as you say it owes me nothing after 20 years and 190K miles.

 

[mrrsm]

These ATSG Resources may prove helpful with all 4L60E and Later Model Transmission Diagnostics:

 

[Mooseman]

The only connection really is when you move the pedal, it moves the throttle and commands the tranny to shift, either up or down, depending on which way you're going with the pedal. It's all electronic or "drive-by-wire". From what you're saying, it sounds like everything is working the way it's supposed to, the computer is commanding the tranny to shift but the clutches are slipping during the 2-3 shift. Letting off the throttle you're just sending less power to that clutch and it also lets it upshift to 4th. If you were to put the shifter to 2 or 3, it will probably slip when you try to push the accelerator a bit. The RPM will rise without actually shifting.

If it is slipping, the fluid should show some evidence of being burnt.

I have considered your suggestion to change fluid/filter just in case the filter is clogged at this point (if I truly have neglected it for 8 years) but since I have no other symptoms beside the 2-3 slippage I have doubts that would fix anything, and as you say it owes me nothing after 20 years and 190K miles.

I'd still at least drop the pan and replace the filter and fluid. You will also see the condition of the fluid and if there's any metal or a lot of muck in the pan. If it improves with that portion of the fluid replaced, then I'd go for the full fluid exchange.

Edit: But if you are going on a trip and the fluid/filter only temporarily improves it and it fails down the road, you would be in a bad place.