4L80E Shifting While in 1st

[jake20]

And for our regularly scheduled programming of "It's always something", I've recently started seeing bizarre shift behavior:

Here is a quick video of what's going on:

About 2 weeks ago, I was driving the truck around 45MPH, it was in 4th gear with low RPMs. As I'm driving, the RPM suddenly came up a bit as if it had downshifted, even though I hadn't changed pedal input or terrain incline. Figured it was definitely out of the ordinary considering I haven't seen it ever do that. I stopped, shifted into 1st, and began some troubleshooting. Here are my observations:

- Transmission will act normal for a while after startup and driving around
- Once I get over 40MPH, it'll sometimes kick up the RPM and feel like it downshifted, although I don't know if that's the case
- After it goes "bizarre", the truck will then upshift from any position on the shift lever, including 1st
- Upshifts from any position other than Circle D Overdrive are rough
- Upshifts from Circle D Overdrive are normal and smooth
- No amount of shifting corrects this
- Stopping the truck, putting it into park, shutting it off, and then starting it back up corrects the issue for the rest of the trip usually


Another set of observations that could possibly related:

- I start the truck one day after it had been running for a bit, wait light never comes on, whereas it should normally flash briefly if it's already hot
- I start driving around, I notice that my battery isn't charging, my temp gauge reads low due to the reduced voltage, and the cab heater and AC switches don't work
- Clearly some set of systems didn't turn on properly, shutting off and starting back up again corrected the issue
- Electrical gremlins are at it again

These are my observations, I haven't done any deep troubleshooting yet, going to run through some troubleshooting flowcharts soon and see what I can find. Will report back on anything else I see.

 

[Mogman]

Sounds like the run solenoid in your EESS box might be going bad, one of the things it does is excite the alternator, no output from the run solenoid= no output from the alt. that also powers the blower.
I do not see any flash from my wait light when hot.

 

[Mogman]

Next time it does not charge check the IGN terminal on the alt, no voltage would be a good indication that solenoid is intermittent

 

[jake20]

Next time it does not charge check the IGN terminal on the alt, no voltage would be a good indication that solenoid is intermittent

Anything to do with the start system at this point gives me shivers lol, after that entire start switch fiasco a while back. Still need to make a basic start switch write-up since I'm sure others will encounter what I dealt with.

I think I can make it act intermittently like you said by trying to cycle the truck on and off a few times, I'll give that a go and measure the voltage if I encounter it. I've had it happen 2-3 times over the last few weeks.

 

[jake20]

Just an update on this situation, haven’t had a chance to troubleshoot this further but about to do so now that I’ve got a lot of other things out of the way.

As it stands, my A2 truck with the 4L80E acts as such:

- Any time I go drive, it’ll start out fine, TCC lockup works fine, but about after 3-5 minutes in 4th gear doing around 40mph the TCC lockup will disengage, so I’m left with it running in slightly higher rpm. Shutting the truck off and turning it back on always solves the issue.

- Today I had an event where it didn’t downshift from 3rd or 4th and was stuck in one of those gears. Figured it out pretty quick after departing a stop sign. Killing and restarting the truck also solved this issue

Given the nature of this, I’m heavily inclined to believe it’s an electrical computer/sensor fault


Going to see if the transmission light throws any codes, though I’ve never had it light up. Light could also be burnt out lol

Also going to check all the speed sensors and make sure they’re connected fine

Worst comes to worst I also have another TCM I ca swap in and test, though I don’t know if it’s good or not, was off a parts truck

Will keep this posted with what I find.

 

[jake20]

I suppose it's also possible that the TCC brake switch could be intermittent? Reading through this document to cover all my bases before poking it with a stick: https://gear-report.com/wp-content/...ment_7_4L80E-Transmission_Troubleshooting.pdf

 

[Mogman]

You need to get the codes if any, otherwise you are just guessing

 

[jake20]

Well I found part of my problem, the transmission status light is toast. Was trying to read fault codes but it wasn’t even displaying code 12.

 

[jake20]

Alrighty was able to get my codes using the beep mode on a multimeter hooked up to where the light previously was. It's beeping 39 and 68, time to dig into remediation procedures:

39: TCC Stuck "OFF"
68: Transmission Component Slipping

Code 39 clears when power cycling the truck, which exactly matches the issue I've described

Code 68 I'm not sure about, could be related to 39 so I'll see if it clears when I solve the TCC issue

 

[jake20]

Seems I now have a plan of action. I yanked a TCC out of parts truck that had the transmission pan missing to see what it looks like and what I'm dealing with.

Here's a video of the one I yanked out of the dead parts truck, per the manual it looks like it's perfect (10-14 ohms resistance). Though I wouldn't put it into my truck as this one has been sitting covered in sand for a few years.

Going to run through the flow chart test procedure in the manual I pasted above, but I have reason to believe that the solenoid in my truck is actually bad. Once I verify with the flowchart I'll get a new solenoid ordered for my truck if that's the case.

One thing I'd like to ask is if there's anything else I should swap while I'm down there. I'll swap the transmission filter again since I'm already going to be down there and it takes 2 seconds to do. The solenoid itself takes maybe 60 seconds to do once you've got the pan dropped. It's just getting to the point where you have the pan dropped is where the effort is.

Much excitement

EDIT: Could overfilling the transmission cause issues with said solenoids engaging?

 

[Retiredwarhorses]

Seems I now have a plan of action. I yanked a TCC out of parts truck that had the transmission pan missing to see what it looks like and what I'm dealing with.

Here's a video of the one I yanked out of the dead parts truck, per the manual it looks like it's perfect (10-14 ohms resistance). Though I wouldn't put it into my truck as this one has been sitting covered in sand for a few years.

Going to run through the flow chart test procedure in the manual I pasted above, but I have reason to believe that the solenoid in my truck is actually bad. Once I verify with the flowchart I'll get a new solenoid ordered for my truck if that's the case.

One thing I'd like to ask is if there's anything else I should swap while I'm down there. I'll swap the transmission filter again since I'm already going to be down there and it takes 2 seconds to do. The solenoid itself takes maybe 60 seconds to do once you've got the pan dropped. It's just getting to the point where you have the pan dropped is where the effort is.

Much excitement

EDIT: Could overfilling the transmission cause issues with said solenoids engaging?

a transmission is a hydraulic pump, over filling is as bad as not enough fluid…

 

[jake20]

I’ve found that continuity between the R and S pins on the J1 connector is spotty. If I wiggle the cable I get a few beeps from the multimeter. Going to open up the connector sleeve and see what’s up. I’m hoping it’s a flaky wire and I don’t actually have to drop the pan now heh

Yea I figure I’d ask but my fluid level is good based on the procedure from the manual

 

[jake20]

I wasn't seeing the results I was quite expecting from the troubleshooting flowchart, so I checked 2 other trucks to verify my sanity and the results were the same with the multimeter.

At this point, I figured I'd start with the easy stuff and just swap the TCM to see if the issues follow it or the truck. Swapping the TCM is easier than dropping the pan. I threw in the spare TCM, installed a new trans caution light, and began my testing.

Took it for several drives, all of which I performed exactly as I had previously when I had the issues occurring. Not a single time across several drives did the transmission do anything out of the ordinary. I manually tested the TCC several tens of times and it worked flawlessly. Get up to 4th gear, let the TCC lock, drive for a bit, lightly touch the brake pedal, and hear it unlock with slightly higher revs.

Transmission light itself never lit up except while the truck was in "wait" mode prior to starting. No codes except code 12 persisted afterwards, so it's void of any faults as it stands.


I'm thinking it's one of two things:

- My existing TCM was going bad
- My existing TCM just needed a power cycle by being fully disconnected from all power for a while

The spare TCM had been sitting on a shelf for a few months, so it's had a good amount of time to drain itself of flea power.

I'm going to test this for a few more days, then I'm going to swap my original TCM back in and see if the issues come back or not.

 

[Mogman]

I wasn't seeing the results I was quite expecting from the troubleshooting flowchart, so I checked 2 other trucks to verify my sanity and the results were the same with the multimeter.

At this point, I figured I'd start with the easy stuff and just swap the TCM to see if the issues follow it or the truck. Swapping the TCM is easier than dropping the pan. I threw in the spare TCM, installed a new trans caution light, and began my testing.

Took it for several drives, all of which I performed exactly as I had previously when I had the issues occurring. Not a single time across several drives did the transmission do anything out of the ordinary. I manually tested the TCC several tens of times and it worked flawlessly. Get up to 4th gear, let the TCC lock, drive for a bit, lightly touch the brake pedal, and hear it unlock with slightly higher revs.

Transmission light itself never lit up except while the truck was in "wait" mode prior to starting. No codes except code 12 persisted afterwards, so it's void of any faults as it stands.


I'm thinking it's one of two things:

- My existing TCM was going bad
- My existing TCM just needed a power cycle by being fully disconnected from all power for a while

The spare TCM had been sitting on a shelf for a few months, so it's had a good amount of time to drain itself of flea power.

I'm going to test this for a few more days, then I'm going to swap my original TCM back in and see if the issues come back or not.

What about the J1 connector?

 

[jake20]

What about the J1 connector?

All my continuity test results were the exact same across 3 trucks, so I figured it's probably not a connector / wiring issue. I just made sure the contacts were clean when I put it back together with the spare TCM for testing, and it seems to operating perfectly thus far.

 

[Mogman]

All my continuity test results were the exact same across 3 trucks, so I figured it's probably not a connector / wiring issue. I just made sure the contacts were clean when I put it back together with the spare TCM for testing, and it seems to operating perfectly thus far.

This is one of my shortcomings, Logically you should have tested it after cleaning the contacts but before swapping the TCM.
I do this same kind of thing all the time, then I am left wondering where the actual failure was.

 

[jake20]

This is one of my shortcomings, Logically you should have tested it after cleaning the contacts but before swapping the TCM.
I do this same kind of thing all the time, then I am left wondering where the actual failure was.

They weren't specifically dirty but I did blow them out with some contact cleaner and air, I'll know more once I swap my original TCM back in after a few days. Definitely a riddle of sorts. In any case, I can certainly relate, sometimes jumping 2 steps ahead just happens

 

[loosegravel]

They weren't specifically dirty but I did blow them out with some contact cleaner and air, I'll know more once I swap my original TCM back in after a few days. Definitely a riddle of sorts. In any case, I can certainly relate, sometimes jumping 2 steps ahead just happens

It’s called “the path of least resistance.” Much like the path that electricity follows, we often follow that same path. You’re not alone my friend!