silverado severe shifting

[egbinor]

I have a 2002 3/4 silverado pickup that has started to shift with a loud clunk. This is not the clunk folks talk about when going from fwd to reverse etc. It has a code of 1870 and when I erase it the check engine light goes away and the problem goes away. On a test run of about 3 miles it works perfect but I have driven it about 20 miles and the light will come on again, the shift will get severe and I can delete the code and the problem goes away, apparently until it gets good and warm??? I'm using an old actron reader that only tells me it's a tranny problem. 120K and I changed the fluid at 75K and it didn't look too bad. Probably spent 15K either hauling a camper while pulling a boat for maybe 10K and pulling a 26Ft trailer for 5K. Any help or ideas appreciated EGBinOR

 

[David G]

I would change fluid again, you are 45K on your next change.

I do not go more than 50K on a change.

 

[Hobo,NC]

You have a valve body issue google it...

 

[Russ from MN]

Are you in tow/haul mode?

 

[Sprint 6]

The 1870 code means it is slipping and does not know why or what component. The harsh shifting is the PCM commanding max fluid pressure to protect itself. Your post is confusing because you say it is a 3/4. 1870 is usually seen on the 4L60E in the half tons because the computer only knows crank speed and out put speed, figures the rest by math and assumed gear ratio. On the 4L60E, it is caused by wear in the valvebody TCC bore. But a 3/4 should have a 4L80E, which rarely would set an 1870, because the 4L80E has a speed sensor on the input shaft, output shaft, and crank speed, so it can tell where the slippage is occurring and will set a code as such. More info is needed your truck.

 

[David G]

Thanks for the description, very enlightening

 

[4play]

P1870 is not really undetermined slippage, this code only sets when excessive TCC slippage occurs. Im pretty sure this is the only "slippage" code a 4L80 will set, though there are other codes that will set due to incorrect gear ratios, those codes are in the P0750's range.

Anyway, this code can be difficult to diagnose since many things can cause the same problem. If you want a "most likely" cause then I would say its the torque converter, but could be other things like the valve body, TCC solenoid etc.

 

[Sprint 6]

If the converter slips on a 4L80E, it will set a specific code for converter stuck off, P0741 I believe. It can do this because it knows crank
speed and input shaft speed. You are correct that the 80 will set incorrect gear ratio codes, it can do this because of the 3 speed sensors.
The ratio codes can then be used to trace to a single component. I have never seen a P1870 on a 4L80E, not that it can't happen.

The P1870 on a 4L60E is usually associated with the converter slipping, but does not have to. The 1870 actually means something between
the flywheel and output shaft is slipping. A 4L60E cannot set ratio codes as a 4L80E can because it does not know input speed. The 1870
code was such a problem GM tried adding an input speed sensor in the pump on the 4L60E in '07 to enable ratio and specific converter
codes. As far as I know, that was abandoned because of unreliability of the sensor setup, the input shaft's small diameter made it hard to
do. I got out of GM dealer's in '09, decided I should be getting paid for my knowledge and work instead of fighting flatrape.

 

[john in la]

It is throwing that code because it can not determine where the slippage is.

Most likely guess.
You have a converter problem.
Known flaw in the 4L80E.

Google "cracked converter clutch piston in 4L80E" for better explanation.

There is a aftermarket upgrade available.

 

[Sprint 6]

I wouldn't say the converter is a "flaw" in the 4L80E. GM got a bad supply of converters in '08ish, which caused problems. The 4L80E is a rock solid trans, it is a TH400 with an overdrive unit in front. Some parts even interchange with the 400. In my 10 years building transmissions at GM dealers, I never saw an 80 die a natural death, it was always a mis-build or a kid in a mud hole. The 80 was so tough, it was upgraded to 4L85E and used behind the Duramax in vans.

 

[Geo-TH,In]

David,
This might surprise you, I may be cheap but when it comes to transmissions I leave that to the pros. There is a place in town that I trust and have used for 40 years.

I trust him to service my transmissions before I have a problem.

He says I'm unusual, most customers wait so long they think their transmissions need serviced when they actually need rebuilt.
geo

 

[David G]

I will state that I have no knowledge in this area, but am enjoying learning with the dialogue.

Thanks.

 

[hd6gtom]

Just got 1 out of the tranny shop. 1st thought it was a wore out torque converter at 260000 miles. They found the valve body had a problem. They dropped the pan fixed the valve body, $125.00 later was good to go.

 

[Hobo,NC]

Converter issue are not the valve body is gonna get a update for that code... That's a good price BTW...

https://www.motor.com/magazine-summary/deciphering-gm-transmission-dtc-p1870-june-2006/

 

[deerlyparted]

I had same problem on my 2000 GMC 2500 with 4L80E transmission. Had to go thru a certain shift pattern to act up but would then kick hard between shifts. I messed with replacing the shift solenoids to no avail. Finally switched out torque converter for <$200 bucks and wow, problem fixed. That was at about 70,000 miles which was about 80,000 miles ago. No more issues.

 

[BobReeves]

You guys were lucky to get away that cheap. When the transmission in my 2000 1500 4wd started shifting hard at 250,000 it cost me $1,700.00.

 

[egbinor]

I definitely have a 3/4 ton 2002 with a 4l80e tranny and 6liter gas engine and aren't in trailer mode when this happens. I once thought that erasing the code fixed it temporarily but now realize that isn't the case, it apparently just cools off and then works ok until it is thorougly warmed up and then starts the harsh shifting.

 

[Hobo,NC]

Gunna throw some numbers out off the top of my head...

$800 labor to yank it and throw a converter at it, Converter $300 and lets say plus 10% and the cost of other parts $200 so you are at $1450.00 no grantee whut you gonna do...