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GM 4L80E Transmission Lockout Problem Fred T. Hart Jr. 2-24-08  
GM 4L80E Transmission Problem:

I have a 2000 model old style Chevy 3/4 ton with 350 engine and 4l80E transmission. Truck has 80K and transmission was serviced at 60K by GM dealer.

My transmission works properly in all gears on level roads. On a hill it will kick out of OD, it will not shift back to OD when the road levels out. When this happens, the shifts from 1 to 2 to 3 are harsh or jerky shifts not as normal. I can turn engine off for 15 seconds, then restart engine and transmission works fine, until I get to the next hill.

Have had codes checked by local auto parts stores, not GM dealership, but so far no defect codes are noted, also no engine service light has come on.

Could this be the cause of my transmission OD problem?

To prevent the OD from burning out (from constant 3-OD up and downshifting and straining the OD) when towing something under load, the trans will force itself out of OD into 3rd when it detects that the converter is not locking up, The factory converter has an internal clutch that controls the lockup of the torque converter, and this clutch's torque capacity is minimal. Hence, if the clutch is going bad, just the weight of the truck and torque required to pull it will force the TCC to unlock the converter and a downshift to 3rd will occur. It will soon be time to replace the converter.
Note: DTC 83 - Torque Converter Clutch
Re: GM 4L80E Transmission Lockup Problem Murray Frater 12-12-08  
Hi can somebody help please.
I have a 1994 fleetwood fair and the 4l80e goes into O/D but not lock up as when I touch the brake at running speed the revs do not increase and the fuel econ is bad.
Sincererly Murray Frater
Re: GM 4L80E Transmission Lockout Problem Bob 2-18-09  
Just purchased '03 Yukon XL 3/4 ton - 67,000 mi - 6L engine 4L80e trans - 4wd: On a straight & level freeway @ hiway speeds the TC will suddenly unlock - stay unlocked for a few miles then lockup again. It has done this 3 times in 50 miles. No error codes set. Salesman says this is "normal". What's going on?
Re: GM 4L80E Transmission Lockout Problem HOWARD 7-19-08  
I HAVE A 96 CAD.deville with a fwd 4l80e trans it went bad i bought a replacement for it. it still dont work. a frend told me i got a bad one so it was replaced again. the car still dont move any ideas???
Re: GM 4L80E Transmission Lockout Problem Fred T. Hart Jr. 3-7-08  
Had codes checked on transmission.

Problem is a busted piston in torque converter.
Hard to believe this transmission would go out for that at 80K. I would have thought that the 4L80E was a stronger transmission. As this one has been service properly and never used to pull over 6000# and did that rarely.

Just my luck to buy a truck with weak transmission.

Guess I will look at the Dodge diesel with manual transmission next time.
Re: GM 4L80E Transmission Lockout Problem Bill Sween 10-10-14  
I replaced my brake light switch and it fixed the problem but my transmission had already been damaged by the time I got it fixed.
Re: GM 4L80E Transmission Lockout Problem rich 3-1-08  
Fred, 1st check your brake light switch. If the switch is out of adjustment or going bad and makes contact, it will unlock the torque. The trans will not stay in overdrive if the torque will not lock. It's the first thing we used to check on an overdrive problem and the simplest to fix. Rich
Re: GM 4L80E Transmission Lockout Problem Gil 4-24-08  
Hello, I have a 95 G3500 GMC and I have the same problem. I found that the throttle position sensor (on the side of my injector pump) is the possible problem along with the computer going into limp mode when I floor the pedal for passing speed. All I do is sycle the ignition switch three times and it resets the computer and the shift problem goes away until If I only press the pedal 3/4 of the way to the floor it seems to be ok. I haven't tried another TPS because it cost a hundred bucks and I'm not sure if it will cure the problem. As long as I know what to do to keep it shifting i'm going to leave it that way. Gil
Re: GM 4L80E Transmission Lockout Problem ali 3-3-09  
Ben oto tamirci ali turkey envoy marka oto 2004 model 50 km den sonra şanzuman vıtes degıştırırken vurma yapıyor neden acaba tesekkurler
Re: GM 4L80E Transmission Lockout Problem fossel 10-29-11  
2004 Silverado 2500HD 4L80E trans. 6.0litre. when towing my fifth wheel in overdrive the torque converter will unlock as I approach a grade. The converter will not lock up again, rpms increase, shifts are hard and engine runs hotter. The truck will return to normal after it is shut off. The problem returns when I approach the next grade. If I manually down shift from OD to 3rd ( before torque converter unlocks)the problem stays away. Where is this defective valve (that I have read about) that is a common cause of this problem. Is it in the converter itself of is it in trans valve body?
Re: GM 4L80E Transmission Problem Justin 11-19-11  
I just bought 96 chev 2500 with the 6.5 turbo diesel. New issue has began, pulling trailer 30-40 miles it starts with over drive then works way down but it pops out of gear. Then if you leave truck cool down it works again. Can any one help me, please?

Thank you
Re: GM 4L80E Transmission Lockout Problem walter 12-22-09  
Can you tell me if this code po894 is a torque converter problem
Re: GM 4L80E Transmission Lockout Problem Philip Levin 10-3-10  
I have a 1996 k3500 chevy with a 454 and 4l80e and the torque converter wont lock up untill traveling at 70mph in any gear. I have had the truck at transmission shops and they can't find the problem. I've also had the truck at the dealership and had the computer reflashed and still nothing.
Re: GM 4L80E Transmission Lockout Problem bob 10-1-10  
Have 04 2500hd with 4L80e trans.the torque converter will lock up as it is supposed to when i first start driving but after 10 or 15 minitues it unlocks. the trans shifts great all the time. it's just the converter that's giving me trouble. the dealer can't find what's wrong. any ideas? thanks,bob. ps, the truck has 79000 miles on it.
Code po894 nick 7-1-10  
I own a 2005 gmc 3500 van and the transmition code po894 comes up how can I fix the problem without spending a fortune?
Re: GM 4L80E Transmission Lockout Problem Brad 6-10-10  
I have the same problem with po894 code could someone tell me what the fix could be without spending thousands of dollars thanks
Re: GM 4L80E Transmission Lockout Problem Michael S. Susi 4-4-08  
Exact same issue....replaced all speed sensors, shift sensors, tcc sensor, throttle position sensor, had the trans flushed and new filters with no improvement. Some times it will go 150 miles of interstate driving in OD and then drop out all of a sudden, especially when I have to hit the brake and then resume cruise control. My local dealer just wants to put a transmission in it but I have taken this truck from Maine to Florida and back with no issue (except the OD shift which we are discussing. If it is as simple as a brake light switch I will be happy and yet angry at the same time for wasting all my time and money.
Re: GM 4L80E Transmission Lockout Problem mr ansari 6-7-09  
I have a suberban 3500 with 4l60e transmission and i have aproblem in shifting so when i stop after driving about 10 miles and start driving again the transmission shift hardly in all speeds.
Re: GM 4L80E Transmission Lockout Problem Tom Randolph 4-10-08  
I have a 91 C3500 dually with 7.4 and 4L80E. On a flat and level road about 65+ mph the Converter will momentarily kick out and right back in. There's no check engine light and no pattern. I replaced the TPS for a former prob lem and this problem started up. Any suggestions?? Thanks.
Re: GM 4L80E Transmission Lockout Problem 6fizzle with 480le easy converter fix 11-20-09  
I too began havin trouble with my torque converter locking and unlocking erratic shifts and i too have felt the burning of my face as my tuck would kick into limp mode right in the middle of a seldom thought out showing off..i even lost some of my jokes. why because i installed a k@n filter and opened up those tiny little slits in the upper intake, it baffled me for some time but became clear after i installed a 10k resistor and pot betweenon the harness to the map sensor.. as far as i can tell this is what happened the increased airflow into the motor due to better breathing tripped my map sensor into telling the computer to de-fuel or go into limp mode because of to much boost 6psi instead of 4 ooooooooooonoooooo anyway this also affects the torque converter since it's also electronically controlled and since i tricked my map sensor with the 10k resistor and pot my tranny also mysteriously was cured hope this helps.
Re: GM 4L80E Transmission Lockout Problem Tom Randolph 5-14-08  
Torque Converter lockup problem finally went away-----I hope!! I replaced the throttle position sensor that I had installed earlier and so far it hasn't kicked in and out of converter lockup. Evidently the first one I bought was defective....who knows. It never showed a check engine light.
Re: GM 4L80E Transmission Lockout Problem keith freeland 1-4-09  
I have 93 chevy 3500 with 6.5turbo and just put in a used 4l80e the old one went out and this one will go threw all the gears perfict but lock up most of the time kicks in and out.what do you suggest and if no fix can i unhook the lock up.
Re: GM 4L80E Transmission Lockup Problem henry 6-28-14  
The car doesnt want to move forward or backwards it is
it is a 2005 cevrolet 3500 silvarado dump truck
Re: GM 4L80E Transmission Lockout Problem leroy Black 2-12-09  
Have 4L80E in 2006 2500 with 57,000mi. has all four gears but no lockup Has code Po894 slipping components will turn on chek engine light after a while. can clear the code and will shift gears normally but no lockup and after a 5 to 10 mile drive will shift hard but stll no lockup.
Re: GM 4L80E Transmission Lockout Problem mark 3-12-09  
I have a 2007 2500 gmc van 4l80e transmission and it comes in hard after 10 miles than it shift hard and once i stop for 15 mins or so it shifts fine for ten miles
Re: GM 4L80E Transmission Lockout Problem Chris 12-4-11  
I have an older chevy that does the same thing, I have heard there are many things that can cause this. Some simple solution problems could be bad temp sending unit on the motor, bad throttle position sensor. Or it could be a torque converter problem or it could be in the valve body. What I do know is it is not normal, and make the dealer fix it while it is still warranted or you will be holding the bag when it goes down
Re: GM 4L80E Transmission Problems Dean Slim 11-9-10  
I replaced my tranmission (4L80E autmatic) on my truck (97 GMC 2WD 3500) with a used transmission that had 89K, my exisitng tranny lasted 287K. The replaced tranmission ran fine for 500 miles, but now experiencing shifting issues; it won't shift into 3rd and OD causing it to run on a higher rpm.
Re: code po894 roy 9-18-10  
I have a 2007 Silverado 1500HD that is reading a po894 code. The dealer says it means the turbo component is slipping and of course GM isn't going to repair it even though I have great service records it has a little over 100k miles. It has a harsh shift and it over heated one time. Can anyone tell me if this is a simple trans repair or will I need a new or rebuilt transmission? I am certain I've paid cash for my last GM product. I would be greatful for any knowledge anyone would have!!
Re: code po894 Robert 4-5-13  
Code po894 on 2004 chevy s10 with 6 cyl engine 4x4
Re: code po894 antonio 11-17-10  
2007 chevrolet van 4.8 code po894
Re: 1996 Chevy G10 4L80E Tranny radiokev 11-9-10  
I just had my transmission done twice with the same problem runs fine but when I step on the gas a little It doesnt shift pass 1 and 2nd. I changed the TPS " Throttle Position Sensor" any suggestions. Please help
Re: GM 4L80E Transmission Lockout Problem Derek 8-25-12  
Hi, I am having the same problem as you had with your torque converter and was just wondering if y ou found out what was causing the problem. Thanks
Re: code po894 dean 7-11-12  
I have 2003 chevy 3500 cab n chassis.
what is the fix for the code po894
Re: code po894 nancy 6-24-11  
What does PO894 mean on a 2005 chevy siverado pickup...I need to know now please
Re: GM 4L80E Transmission Lockout Problem Ken 12-8-15  
4 l 80 E transmission will not go into gear when I put it in drive very sluggish then after a few minutes of driving down the road it slips into gear and runs just fine until I switch out of gear then it does it all over again. getting worse each time I do it also has no power going up hills.
Re: code po894 john 10-23-12  
05 avalanch what is fix for this code tranny shop never heard of it
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