Uh oh....possible 4L80E trouble....any input?

[STINEY]

So I finish up rebuilding the bedroom floor of the rental last night, new joices/decking/carpet, yeehaa.

And on the way home in the van, I notice that the 1-2 and 2-3 shifts are VERY firm, like some sneaked in a stage IV kit or something when I wasn't looking.

Then a few miles from home (25 mile drive) the check engine light comes on.

Checked trans fluid, seems okay, might have been a touch low (I changed the trans filter, cleaned the pan, and refilled last fall) so I added a quart. CEL still on after a restart.

Checked again this morning after it was stone cold, still has CEL.

Am I in deep transmission doo-doo? Any pointers?

(If it ain't one thing, its another. Didn't realize Murphy was stalking me until last night....)

[STINEY]

After speaking with my buddy who has a shop (and the $$$$ real scan tools) he said to bring it over, and not to stress too much over it. Apparently the computer needs several inputs (wheel speed, outputshaft speed, throttle position, and several others) that it uses to determine line pressure, amongst other things.

If it loses one of those inputs, it doesn't know what to do, and defaults to a closed loop mode that includes highest line pressure. That way you can "limp" home without damaging anything due to slippage.

Hopefully it will be cured Saturday.

[TC]

If the CEL is on, that means it threw a code, have you checked to see which code it stored??......

[SpiderGearsMan]

Check Charging Volts ..under 11.7 puts it in full line pressure

[Mr4Speed]

Do you know which code it has? Some of the transmission codes command full line pressure until reset.

[SpiderGearsMan]

could eat the center support

[STINEY]

The saturday buddy shop deal will be where I get the codes, will probably be fixed same day too unless its more than a sensor. He's no hack, independent but professional.

Check Charging Volts ..under 11.7 puts it in full line pressure

Hmmm.....I'll check that tonight. Although I drove home last night after dark, and headlights never went dim in 25 miles.

could eat the center support

Would it do that from increased line pressure, or are you saying that could be what the problem is?

[min301]

The saturday buddy shop deal will be where I get the codes, will probably be fixed same day too unless its more than a sensor. He's no hack, independent but professional.



Hmmm.....I'll check that tonight. Although I drove home last night after dark, and headlights never went dim in 25 miles.



Would it do that from increased line pressure, or are you saying that could be what the problem is?

He said that from the hard shifts...they will beat up the Center support.

[bulletproof]

when my 4l80e eat itself it started with a very hard shift,,and turned into a screaming grinding freight train sound,,

[STINEY]

Errrr...that's not real encouraging friend.......let's hope my luck is somewhat better? My wallet hopes so anyways.


Well, today wasn't exactly a success. Made it to buddys garage, hooked to Genisys scanner tool, and after verifying a bunch of functions we took it for a ride. Clearing the code PO894 makes it shift normally, but in a couple of miles of stop-n-go driving it starts again with the firm shifting.

Here's the weird part. It only throws the code once you are at cruising speed and everything is locked up. No code setting while 1-2 or 2-3, it only repeatedly did it once settled in and cruising along.

And the ECL only comes on after it throws the code 3-4 times. This is normal though according to buddy. The other part has him a bit confused though.

We did change the Pressure Control Solenoid Valve Assembly #320 and it did have an immediate difference in the "feel" of the vehicle, but did not change the problem.

On the way home I put it in TOW/Haul mode, and the CEL did not come on until I took it out of Tow/Haul about 1/2 mile from home. Also no hard shifting until last 1/2 mile either.

Coincidence or not?

Doing more research now....

[SpiderGearsMan]

He said that from the hard shifts...they will beat up the Center support.

snap ring tears into
which is why I don't like the 4L80e

[JOES66FURY]

After speaking with my buddy who has a shop (and the $$$$ real scan tools) he said to bring it over, and not to stress too much over it. Apparently the computer needs several inputs (wheel speed, outputshaft speed, throttle position, and several others) that it uses to determine line pressure, amongst other things.

If it loses one of those inputs, it doesn't know what to do, and defaults to a closed loop mode that includes highest line pressure. That way you can "limp" home without damaging anything due to slippage.

Hopefully it will be cured Saturday.

was going to say the same thing...I had to change the computer to fix my issue...ran thru 5 coumputers until GM got me one that was good...apparently there was a big issue with their computers during that time.

[STINEY]

What year was your issue with Joe?

[JOES66FURY]

91 3/4t Chevy Suburban, once I got the computer sorted out I had no issues with the truck.

[anotheridiot]

We tried to rebuild a 4L80E, ended up replacing it with a rebuilt. The pump was bad. Check your pressure if you can find out what its supposed to be at your cooling line. Then add an inline filter to protect the new one. He said you can trash the trans within 10 miles with a bad pump.