Tranny Woes

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?

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

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

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.

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

gmartin1215 said:

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?

Click to expand...

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...

NickTransmissions said:

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...

Click to expand...

The tranny was the only thing failing

gmartin1215 said:

The tranny was the only thing failing

Click to expand...

See below.

NickTransmissions said:

What kind of code reader do you have?

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

Click to expand...

NickTransmissions said:

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...

Click to expand...

Innova 3160

gmartin1215 said:

Innova 3160

Click to expand...

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.