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4L80e in Hummer started slipping when warm....

Sand

Active Member
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Location
Canada
Thread starter #1
My 4L80e in the Hummer just started acting up....
No codes. Works fine cold. When warm looses OD, then third. Then starts slipping in first and second...
Fluid is fresh one year ago. 100 000 miles.
Dipstick is showing fluid. Strangely there is loads of rust at the top of the dipstick....thats new since I last checked it but its been a really wet damp winter.
Just got home and first code poped
P0236.
I had it last week and changed the MAP sensor today. Guess I was wrong for 84 dollars...lol
Ill search the threads in a couple hours for a similar issue.
Sand
 

THEFERMANATOR

FRANKENBURBAN
Staff member
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Staff #2
If it happened suddenly, there's always a chance the filter seal dropped down, and it's sucking air. Or your pressure control solenoid has failed. All you can do is put a pressure guage on it, and see what's going on. Also look at the fluid and see if it looks milky or aerated, if the filter seal goes, the fluid will start frothing, and look milky from all the air bubbles.
 

WarWagon

Well it hits on 7 of 8...
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#4
Rust on the dipstick can indicate coolant leaks like the radiator heat exchanger having a pinhole. A oil sample of the trans oil can rule this out esp. before you ruin a rebuilt transmission. Set sample aside to send in later in case minor fixes don't work.
 

MrMarty51

Well-Known Member
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#5
P0236 code
Check the vacuum, clean all terminals at the back of the engine, if it is like the GM400 with several connectors back there.
I had quite a struggle getting so the truck would not trip that code.
 

Will L.

Well-Known Member
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Boulder City Nv
#12
Rust on the dipstick can indicate coolant leaks like the radiator heat exchanger having a pinhole. A oil sample of the trans oil can rule this out esp. before you ruin a rebuilt transmission. Set sample aside to send in later in case minor fixes don't work.
Hummer do not have the trans fluid go through the radiator. Complete seperate cooler. No way for atf and coolant to exchange. Pickups have a lil cooling stack, hummers have a STACK. Also seperate oil cooler like pickups but larger, a power steering cooler, and of course ac condensor.
 

Sand

Active Member
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Canada
Thread starter #13
My first check was transfer case too full. Trans fluid goes through a heat exchanger in there.
No dice...that would have been too easy.
 

Sand

Active Member
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Location
Canada
Thread starter #14
Local transmission place lent me a known good pressure solenoid. Swapped it out. No change. Still downshifts and winds out in lower gears. They lent me a output/input speed sensor too. I swapped my input out first. No change. Then swapped my output out....no change...Boo.
 

Sand

Active Member
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Location
Canada
Thread starter #16
Sooo. My torque android app is not picking up TCM vodes.
A proper OBD tool is now showing P0730.
Thats better.
 

monka

New Member
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Location
Ontario
#17
I'd would have done the full solenoid kit change, it's cheap
Possibly shift solenoids, but you have some done now, hopefully it not major.

Lol, this way you've covered most bases, I lost gears, as well (felt like neutral) stop, then it would work again, that kit cured it, now 3 years later all is smooth still,
 

THEFERMANATOR

FRANKENBURBAN
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Staff #19
P0730 is an incorrect gear ratio, aka extreme slippage code. My best advice I can give is STOP throwing parts at it, and get a pressure guage on it. Or for a simple test, unplug the main electrical plug from the transmission, and see what it does in limp mode. You should have reverse and 2nd, but if you feel slippage in limp mode, your problem is definately something major inside the trans like a cracked accumulator piston, or busted servo piston.
 

Sand

Active Member
Messages
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Location
Canada
Thread starter #20
I know....Im sorry!!!! Im the guy I warn people not to be....Im not a tranny pro yet and have no pressure guage. On my list. Its a long weekend and at my level all I can do is try new parts. So far no investment other than beer for solenoid loan. 50 bucks buys new shift solenoid's as its wed before I can have the thing looked at properly. The pan is off and I know its B grade but Ill try it anyway.
 
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