Tranny Woes

[gmartin1215]

I have a 2009 Tahoe 5.3 with the 6L80 and about 150k miles.

I just returned from a long highway trip towing a small boat and camping gear in the back of the Tahoe.

While driving on the highway, the tranny suddenly went out of gear (think I was in 4th or 5th), and all the lights turned on in the dashboard, and the tach went high when it got out of gear. I let my foot off the gas, and the tranny re-engaged, the lights went off, and we continued on. I was also get some slipping out of gear when towing it in town, but putting it in tow mode seemed to alleviate that.

I Continued with the trip and had no other issues until I was driving back home, and the same thing happened again on the highway where it went out of gear, and I had a Christmas tree dashboard. Let off the gas again and tranny re-engaged and lights went off. I continued driving for several hundred miles more and got it back home.

I put the code reader on, but there were no codes stored.

At this point, I am thinking that the tranny has gone bad and time to fork the big $$$$ for another one. But, since it was not consistently doing that, I am wondering if there may be something else going on that should be checked/replaced before getting a tranny.

BTW...anyone in the Colorado Springs area knows a good tranny shop that knows these trannies?

 

[Fless]

Is the hot tranny fluid up to the correct level on the dipstick? What does the fluid look like?

 

[swathdiver]

I would be doing an electrical check first if all your lights came on. Check the tightness of your battery cables and for corrosion.

Ever hear of this Nick with the 6L80? @NickTransmissions

 

[petethepug]

Keep your code reader plugged in at all times to capture the DTC if you can. First & formost replace -/+ battery cables if you have not already. They rot (invisibly) from the inside out and do cause weird ship to happen just like you’re experiencing. $100 cables and the problem mysteriously disappearing is better that a $5k (unnecessary) trans replacement.

If the trans fluid looks and smells ok, those cables may be the Hail Mary cure.

 

[j91z28d1]

you could send off a fluid sample to black stone. they might be able to tell you something about the amount of wear.

 

[NickTransmissions]

I have a 2009 Tahoe 5.3 with the 6L80 and about 150k miles.

I just returned from a long highway trip towing a small boat and camping gear in the back of the Tahoe.

While driving on the highway, the tranny suddenly went out of gear (think I was in 4th or 5th), and all the lights turned on in the dashboard, and the tach went high when it got out of gear. I let my foot off the gas, and the tranny re-engaged, the lights went off, and we continued on. I was also get some slipping out of gear when towing it in town, but putting it in tow mode seemed to alleviate that.

I Continued with the trip and had no other issues until I was driving back home, and the same thing happened again on the highway where it went out of gear, and I had a Christmas tree dashboard. Let off the gas again and tranny re-engaged and lights went off. I continued driving for several hundred miles more and got it back home.

I put the code reader on, but there were no codes stored.

At this point, I am thinking that the tranny has gone bad and time to fork the big $$$$ for another one. But, since it was not consistently doing that, I am wondering if there may be something else going on that should be checked/replaced before getting a tranny.

BTW...anyone in the Colorado Springs area knows a good tranny shop that knows these trannies?

Almost sounds like an intermittent, massive electrical failure of some sort. Was the transmission the only component that ceased to function during these episodes or did the engine's behavior/activity also change?

If it is a mechanical issue with the unit, could be front planet or torque converter going bad. Those two things can produce "false neutrals" intermittently.

Can also be a TECHM or CanBus failure but a code would set for those.

What kind of code reader do you have?

Budget code readers typically can only pick up emissions-related DTCs...

 

[gmartin1215]

Almost sounds like an intermittent, massive electrical failure of some sort. Was the transmission the only component that ceased to function during these episodes or did the engine's behavior/activity also change?

If it is a mechanical issue with the unit, could be front planet or torque converter going bad. Those two things can produce "false neutrals" intermittently.

Can also be a TECHM or CanBus failure but a code would set for those.

What kind of code reader do you have?

Budget code readers typically can only pick up emissions-related DTCs...

The tranny was the only thing failing

 

[NickTransmissions]

The tranny was the only thing failing

See below.

What kind of code reader do you have?

Budget code readers typically can only pick up emissions-related DTCs...

 

[gmartin1215]

Almost sounds like an intermittent, massive electrical failure of some sort. Was the transmission the only component that ceased to function during these episodes or did the engine's behavior/activity also change?

If it is a mechanical issue with the unit, could be front planet or torque converter going bad. Those two things can produce "false neutrals" intermittently.

Can also be a TECHM or CanBus failure but a code would set for those.

What kind of code reader do you have?

Budget code readers typically can only pick up emissions-related DTCs...

Innova 3160

 

[NickTransmissions]

Innova 3160

Im not familiar with that tool but it looks like a budget-oriented reader which means it's 50/50 as to whether you'd see any transmission, chassis, CANBUS or ABS codes with it but you'd know better than I, especially if you have previously been able to use to to pull such codes.

If the transmission is the only component impacted, my guess it's something electrical, given what you've described thus far, perhaps a short in your vehicle wiring harness or even the ECM or TEHCM.

Your best bet is to attach a scan tool with bi-directional capabilities and take it for a test drive with the transmissions's live data pulled up along with engine data. If the problem occurs while the scanner is plugged in, you should see whats happening on the screen when it acts up. If the fault is something 'hard core electrical' in nature, you may even need an oscilloscope to truly diagnose the problem, which is beyond the scope of my area of expertise (I hate automotive electrical work).

Start with a visual/physical inspection of all your wires, connections, battery and alternator terminal connections. Once you've confirmed there's no issues (or there are and you're able to quickly fix them), plug the scan tool, your current one as shown above or a better one if the one you have isn't capable and take it for a test drive...Let us know what you find.

 

[gmartin1215]

Thanks for the tips.
the tranny was also slipping out of gear without the dash board lighting up. A couple of times in lower gears, but put it in tow mode and that went away. Then it happened again at higher gears in tow mode where it slipped and went out of tow mode, but no dashboard lights. Its all very intermittent. Like I said, the dashboard ligthup and slipping out of gear happened twice, but went back in gear after letting off the gas.

I don't have a scanner to read what the tranny is doing while driving so will have to take it in somewhere that does have the tools. But, I can't always get it to do the problems consistently, unless the previous issues are stored someplace. Very intermittent and drives me bonkers.

Will check wiring again, but did not see any loose connections.
I do have a multiswitch for external lights that does send a wifi signal, but it had been driving fine for a while with that installed and powered.

 

[NickTransmissions]

Thanks for the tips.
the tranny was also slipping out of gear without the dash board lighting up. A couple of times in lower gears, but put it in tow mode and that went away. Then it happened again at higher gears in tow mode where it slipped and went out of tow mode, but no dashboard lights. Its all very intermittent. Like I said, the dashboard ligthup and slipping out of gear happened twice, but went back in gear after letting off the gas.

I don't have a scanner to read what the tranny is doing while driving so will have to take it in somewhere that does have the tools. But, I can't always get it to do the problems consistently, unless the previous issues are stored someplace. Very intermittent and drives me bonkers.

Will check wiring again, but did not see any loose connections.
I do have a multiswitch for external lights that does send a wifi signal, but it had been driving fine for a while with that installed and powered.

If the trans is. slipping, its probably time for an overhaul anyways so don't feel bad if you can't figure it out in the immediate near future...You may be yanking the unit out to have it gone through sooner rather than later...A shop will put it on the bi-directional scan tool and take for a drive to see what's up. Based on that, they may decide to yank off the TEHCM and Valve Body...If they have the TECHM test block (produced by Bosch under the 'Kent Moore' brand name) they'll be able to live test the TEHCM for both electrical as well as mechanical function..I have one but rarely use it as you need the vehicle for that thing.

Anyways, keep us in the loop as to what happens

 

[Just Fishing]

Thanks for the tips.
the tranny was also slipping out of gear without the dash board lighting up. A couple of times in lower gears, but put it in tow mode and that went away. Then it happened again at higher gears in tow mode where it slipped and went out of tow mode, but no dashboard lights. Its all very intermittent. Like I said, the dashboard ligthup and slipping out of gear happened twice, but went back in gear after letting off the gas.

I don't have a scanner to read what the tranny is doing while driving so will have to take it in somewhere that does have the tools. But, I can't always get it to do the problems consistently, unless the previous issues are stored someplace. Very intermittent and drives me bonkers.

Will check wiring again, but did not see any loose connections.
I do have a multiswitch for external lights that does send a wifi signal, but it had been driving fine for a while with that installed and powered.

Check the grounds.
I had one go bad that looked fine, but cutting back the insulation showed me corrosion.
With that one the dash would light up like a christmas tree, engine would stall or lose power.
And it only happened after I drove through a mud puddle and while I had the AC on full blast with the rear AC blowing.

Many of the grounds are under the driver side of the vehicle, you will see them going to the frame.

 

[gmartin1215]

Well, I took it to a tranny shop, one with a good reputation, gave my story and the keys and asked them to diagnose it.


Of course, the tranny would not act up while they had it, and they did do a bi-directional scan while driving it and checking for other codes. The scan revealed nothing out of the ordinary, and there were no error codes.

They did pull the pan and the magnet was only collecting normal wear, and there were no other chunks floating around. Everything else while the pan was off appeared normal, too.

They put it back together and gave it another drive. Still normal driving.

Also had them check all them grounds and they did not see anything loose.

At this point, they told me they could not diagnose it further and to drive it until issues are more consistent.

Unfortunately, the issues are sooo infrequent that it is still a mystery. It is driving normal for now, but who knows when it may fail and why.
I'll just keep driving it until something finally goes.

I might try a different shop to see if they come up with something different, but at this point I may get the same story that they need something consistent to find the problem. I bet if I took it to the dealer they would say, "Yup! New Tranny! That will be $6k, please."

What are some symptoms of a torque convertor going bad?
Shifting sometimes seems sluggish. Asked the shop about it and they said they noticed nothing out of the ordinary. Could be me over think and trying to find issues, though.