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4L80e Transmission dropping out of overdrive - Printable Version

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4L80e Transmission dropping out of overdrive - Roadtripp - 06-07-2019

So I got the 96 Chev G30 Short Bus with 117K miles out of storage a few days ago and excited to start working on changing fluids and cleaning it up. After a day of taking it on test trips running errands it suddenly quit going on the interstate with the engine sounding fine but revving and not engaging the transmission. I was seeing tow bill dollar signs in my head. And transmission rebuild dollar signs and fog horns going off in my head. Then I shifted down and it engaged again as I coasted onto the shoulder with suburus and Hyundai’s piling up behind me. 
  Has anyone had this issue before? I took it out a couple more times and it does the same thing. After a short distance getting up to speed on the highway it drops out. Could that be “limp” mode?. No lights came on on the dashboard. 
 This is a early electronic 4L80e transmission. I’ve read forums and it’s not uncommon. There’s a debate over what the issue is. I changed the filter and some of the fluid after the issue began. That didn’t fix it. 
 One forum said the internal wiring can leak fluid into a connector or solenoid. And a sudden change can indicate solenoid issue. It said worn valve body will be gradual issue. I had been gradually adding more fluid so maybe the fluid got into something it wasn’t supposed to. 
 I’m not sure what people mean by saying the torque converter “locks up” in 3rd and 4th gear. Is that what the torque converter clutch does. Engages and locks it for cruising? I guess I’ll need to read up on it some more. 
 Any light shed on this issue is much appreciated. I’m just getting up to speed on how a automatic functions. 
 If it is limp mode wouldn’t a light come on. 

RE: 4L80e Transmission dropping out of overdrive - sternwake - 06-07-2019

I have an 1989 dodge, but had similar Overdrive issues this time last year. I was prepared to drop the pan and valve body to install a new solenoid pack. Mine has just 2 solenoids controlling overdrive and lock up, as the first 3 gears are hydraulically controlled.

In prepping for dropping the pan and valve body, which was necessary just to get the electrical connector to the solenoid pack in and out, I was wirebrushing, and using compressed air on all the gunk from around the wire connector, to insure that no debris could fall inside when i dropped pan and valvebody. While i was under there doing this, I remembered that i never reset the engine computer which directly controls both solenoids.

So after scrubbing the area near and above the Tx electrical connector clean, I did that, disconnecting the battery for a while, and then aftewards the overdrive never acted up again. Crisis averted.

Now there could have been some issues with the contacts in the connector, which also got some compressed air inside. The connector body faced up and cleaning it out from below with limited access with Q tips and sightline, was not very effective.
So i am not really sure whether resetting the engine computer, which controls the overdrive and lockup, fixed my issue, or the wire connector itself was compromised. I am leaning more towards the ECM reset, but no proof.

All automatic transmissions slip slightly as there is not a direct link between crankshaft and transmission, until the lock up occurs on the torque converter( if so equipped). Mine only locks up in overdrive, which is 4th gear, and the lockup does not occur below 47MPH and is like 5th gear. Rpms drop from about 2250 to 1975 at 65mph when it locks up, and it will not lock up until the engine coolant temp sensor reaches ~70F.

So I would look for the electrical connector at the transmissoin. look for crusty insulation of possiby overheated wires. Use a mirror and strong flashlight to see the pins and barrels inside this connector. The mere presence of Dielectric grease inside the connector, does not mean the electrical connection is solid, as so many people instantly assume.

Caig DeOxit D5 spray is magic electrical juice for electrical connectors. No other contact cleaner comes remotely close, although they are good for blasting out detritus and old Dielectric grease from the connector. The Deoxit can do this too, but is 50% more expensive for 75% less product, and is hard to near impossible to find in stores, Fry's electronics being the only one i know of that carries it.

I'd follow that wire harness, there is likely more electrical connections between it and the engine or possibly transmission control computer and inspect those connectors, all the way back to transmission or engine computer.

Rule out all these exterior electrical connections first, and reset the engine/transmission computer(s), before assuming the problem lies inside the transmission pan.

If they continue,
There is an active member over on Bob is the Oil Guy forums, who goes by the handle of 'Clinebarger', who is extremely knowledgable about GM transmissions, and can probably rebuild the 4L80E transmission in his sleep. I'd want to run those symptoms past him, after insuring all exterior electrical connections are clean and tight.

Good luck.

If you sign up over there and post a question, there is a large percentage of half wits who type and respond with authority, yet have little aptitude and Zero experience, but there are a few who really have lots of both, and 'Clinebarger's' would be the only response I would take seriously, regarding any Transmission diagnostic issue. He is fairly active and it will be a sad day when the screaming, experience free half wits, cause him to stop contributing.

RE: 4L80e Transmission dropping out of overdrive - Snikwahjm - 06-07-2019

We had a problem going home from Florida one time. We got up on 10 and the van didn’t want to move up a grade. Hint: it’s flat... except for ramps and over passes. We got off the highway and limped to a Walmart. We figured out it was water in the gas. We just spent the night at WM after putting dry gas in the tank. In the morning we scooted down the road to home. Made it through the hills just fine.

RE: 4L80e Transmission dropping out of overdrive - Roadtripp - 06-07-2019

Thanks SW, those will be the priorities as soon as these waves of rainstorms passes. 
 And Snik, thanks, but it’s not water. That’s happened however. It can freeze in the fuel line also. Good it was a quick fix for you. What a relief!!
  I’d like to find some Deoxit electrical cleaner. Then go over the connectors. When I determine where the TCU is will clean it also.  And disconnect the battery. 
 I wonder what’s in the Deoxit D5??
  I neglected to mention this fault occurred after I pressure washed the engine. My bad.  The next day when going onto the highway.  I tried to pressure wash it carefully and purposefully didn’t pressure wash the side of the transmission with the electrical connectors. But this may be no coincidence. I’m learning newer vehicles with lots of electronics are different than the older simpler vehicles I used to pressure wash. In this case a rodent had camped out on the engine and made a mess so the clean nazi in me emerged with a pressure gun. 
 With that out of the way I might check out the guy on Bob is the Oil Guy site if I’m still stuck. Some folks are such skilled at what they do. I spoke and watched with a mechanic once who I could tell was a natural. And a electrical engineer who is very skilled: I went to buy a inverter from a guy who turned out to be one of the founders and engineers of Magnum Energy company. It was a pleasure to see him work as we tested the inverter in his garage. Watching a highly skilled person work is interesting.

RE: 4L80e Transmission dropping out of overdrive - sternwake - 06-07-2019

Ahh, the powerwashing could indeed be related.

The first time I felt my Tx inexplicably drop out of OD last year, was after it rained. All it really takes is that tire hitting one puddle shaped in such a way it shot water onto the TX connector.

I had cleaned that connector afterwards and thought it looked wet when i took it apart, but I did not think to reset the computer at that time, and that might have been the cure, instead I stressed over it for a month, keeping it out of OD, then ordering new solenoids, buying 5 Quarts of ATF+4 and filter and gasket kit.


i had no OBD1 codes stored. I had somewhat hoped to find a code 15 for the vehicle speed sensor although the sensor is not too old. Its predecessor had issues with rain water entry into the connector causing intermittent OD, and later the reed contacts inside would stick together. a code 15 on my van does not illuminate the check engine light. yu might have codes stored without a CEL too. i don't know.

i suspect that in my case the rain perhaps did allow some puddle water inside that connector on the transmission. I did discover at that point the little ribbed rubber boot was not really sealing 'locking' upto snuff.

I am not sure what the ingredients are in the Deoxit that are magic. The D series of their product comes in d5 and d100, with d100 being much stronger, but they say excessd100 should be wiped off after a period of time, which is not always easy to accomplish. There are many different methods/products of application. Some come with a longer needle spout, some a brush.

I first bought a DeOxit 'kit' that contained several different products, like Deoxit gold and Deoxit shield in tiny spray bottles and tubes and wipes along with bottle brushes and swabs. A lot of the spray can goes to waste. I like using the little tubes and small swabs or tiny 'dentek' bottle brushes designed for getting inbetween teeth. these are sold at most drug stores/pharmacies/ Chemists for you UK/commonwealth speakers.

Scroll sideways to see all their different offerings.

Try and find a coherently written negative review on any of their products, discounting those complaining about product price.

Sometimes one might be able to find small precision swabs in drug stores, that women use for applying or removing makeup, though i have had no luck and just order these whose heads are abut 1.5mm in diameter:

I still use Dielectric grease, but I do not stuff a connector with the grease and then snap the two halves together, as I feel this can force spring loaded contacts away from each other.

After cleaning the connector with d5, i use Deoxit Shield on the conductive surfaces of the connector, close the connector, then push and smear dielectric grease all around the connector exterior and push it past the wire entry of the connector, if possible.

i have had issues with shield S5 spray, swelling the ribbed connector waterproof boots, then at a later date having issues reconnecting the two halves, so i would recommend not getting the DeOxit Shield S5 spray on silicon/rubber boots.

Audiophile nerds are well aware of DeOxit products. Try it on your phone's Micro USB connector and it will click into place like new, and the phone will likely also charge faster.

My Sisters Iphone stopped charging completely, and rubbing alcohol had no effect. One tiny squirt of d5 on the plug, inserted into the phone and then all was well.
There are countless stories of various failed electronics that someone just sprayed and prayed various orifices withDeOxit d5 and they started working again.

I start getting anxious when my supply is running low.

Products sold at Autoparts stores, like CRC QED cleaner, are great for flushing out old dielectric grease and detritus from electrical connectors without damaging the plastic, but they do nothing for the oxidation on the conductive surfaces.

RE: 4L80e Transmission dropping out of overdrive - rvpopeye - 06-08-2019

Many of the shows I did have this miracle juice to thank for running smoothly. Thus saving my ass and cementing my rep as having the "touch".

Back in their beginning the creating mfg (Caig Labs) called Deoxit "Cramolin"
The #s 5 and 100 are the % of active ingredient and Cramolin red was the cleaner and blue was the preservative , both 100%. I still have a bit leftover that I sparingly use from time to time.............
Guess the company changed (bought out?) and they decided on the 5% strength The amount used was always recc, at minimal and wiping off excess was stressed in the use instructions , so that makes sense .
It probably dissolved things as Stern hinted ?..

Buy it , use it , don't worry about the details ....

Pressure washing a vehicle engine (anything) that has a computer in it is bad Ju Ju.
So many sensors and connectors.........!!!!!!!!!!!!!!!!!!!!!!!!!!!! ?????????????????????
(Think dipping your phone in the toilet !)

Good luck finding your prob.
Hopefully you can do just that and don't have to pay big $ to fix it.

RE: 4L80e Transmission dropping out of overdrive - weigh2ez - 06-08-2019

AMEN on the power washing.  I don't do it anymore either.  If the gunk gets too thick on your engine scrape it off with a knife or something.  I agree with Sternwake about cleaning the connectors first.  It would be a shame to drop the pan and replace parts and then find out the connectors were dirty.  Good luck

RE: 4L80e Transmission dropping out of overdrive - Blacktank - 06-08-2019

another clean the connections

should never use a power washer,a good engine degreaser,elbow grease and rince,cover distributor and/or avoid the electronics as much as you can

if that dont work find a shop and do a diagnostic,should tell you if the electronic side is working,if that comes back good it's the valve body,what color is the fluid?

RE: 4L80e Transmission dropping out of overdrive - Roadtripp - 06-09-2019

The fluid is reddish brown. Doesn’t stink burnt. 
 Today I checked all the small connectors on the transmission and engine too for grins. The wires look ok, connections looked clean, dry, and sealed.looked in distributed cap for moisture. Nothing.  The battery was disconnected to empty codes. The test drive was like a wet dream until after a few miles it disengaged again when I hit 55-60mph. Limped back home to do more reading. Chilton manual says it may be running in the default or the 2nd gear mode. Better than destroying tranny. 
 So by jumping the terminals A-B in the OBD1 port with a small piece of wire it gave the diagnostic trouble codes by blinking the check engine light a certain number of times. Code 68, 74, and 87. On the third and fourth time I counted them correctly. It takes a little practice. It’s a neat feature. 
 Code 68: overdrive ratio error
 Code 74: transmission input speed sensor
 Code 87: high gear ratio error
 I just read in the 4 wheel ABS section that jumping the terminals A-H gives codes for the antilock brake   system which is linked to the speed sensor. I’ll try that tomorrow to see if the sensor code comes up again. And try to get a better idea what those codes mean. 
 Apparently a weak ignition switch sending intermittent power to electric sensors and solenoids can wreak havoc. And the brake light switch can too. 
  Thanks for the ideas

RE: 4L80e Transmission dropping out of overdrive - sternwake - 06-09-2019

On mine most engine sensors are fed only 5 volts from the ECM, and then whatever voltage is returned to ecm through the resistors in sensors allows it to change fuel /air ratio/ spark timing. The lower the voltage, the more susceptible the circuit is to voltge drop caused by poor conductivity inside the connectors.

I was kind of surprised when I cleaned all my engine sensor connectors ith DeOxit, all of which appeared fine. it was like I took 500 LBs out of the back of the van.

Before I was aware of Deoxit I used some of the CRC QED cleaner on my engine computer connector, and thought it was pristine, but then learned about DEoxit and went over the same connector with D5 the bottle brushes and precision swabs and those swabs turned black, then gray and eventually stayed pinkish of the D5. The contacts went from looking like oxidized tin to freshly polished then oiled silver.

My vehicle speed sensor fits on the speedo cable inline, and has a spinning magnet which opens and closes these little contacts called reed switches something like 7 times per 360 degree revolution, which the computer counts to determine the speed and if it is safe to engage overdrive and lockup. At one point thse reed switches would not respond to the magnet, and if Ificked the sensor with my fingers they would break free and OD and lockup would work normally, until the next time the engine sat and the reed switches bonded together closed.

Later versions of my vehicle the speed sensor was on the tranission where the speedo cable exited, then later on the differential housing. not sure what GM does in your model year.

So all that oxidation formed despite the presence of Dielectric grease.

Hope you can find an easy resolution. I'd recommend not dismissing any electrical connection unless it has been 'DeOxited'