96 Silverado - Interesting problem - Transmission Jerk

[Spence Baker]

I own a 96 Chevy Silverado with a 5.0l Vortec v8 and an automatic
transmission with
overdrive. I haven't had any problems with the truck until now.

Symptom:
After driving for a bit, (driving time varies) the service engine soon
light comes on,
and from that point, everytime the truck shifts, it is a SEVERE
jerking between gears. (feels like you are being hit from behind). You can
cut the truck
off for about 5 minutes, and when you start back up, everything is ok, but
the light is still on.

Once again, you can drive for a while, (usually highway driving) and the
problem comes back.
Occasionally, the light does go back off, but usually not for long.

I took the truck to the GM people where I bought it, and they ran their
'diagnostics' on it,
and the truck returned a code of P1870. They had no idea what that code
means. So, they
put a filter kit in the trans. and changed the fluid and sent me home. I
went to a local transmission
guy (really good) and he said that he knew of 3 other Chevy trucks that were
doing the exact same
thing, but still did not know what the P1870 code means. He had a couple of
guesses about the
torque converter, but he didn't want to do anything until the mystery is
unraveled.

My question is, CAN SOMEONE HELP ME... I have already replaced the U joint
in the truck after
it started making noise, and don't want to replace the transmission because
of something that could
be relatively simple. If anyone can help, please post, or email to
sba...@netdoor.com.

Thanks!

[Mark Aarabi]

How the heck can a dealership not know what a OBDII code P1870 means? Where do
they train these guys these days, Chucky Cheese?

P1870 is a transmission code and indicates that PCM has detected a transmission
component slipping. A scanner that can access GM OBDII enhanced parameters
should be used to monitor TCC slip speed. With the torque convertor locked up,
this parameter should be within 50 RPMs of engine speed. Make sure that the
truck is being scanned *during* the problem phase... otherwise this parameter
will probably look normal.

PLEASE let us know the actual fix when it becomes available.

-Mark Aarabi
ASE Master Tech

[SCWrench]

On a long shot have your throttle postion sensor changed as that would effect
your trans upshift/firmness. One other part to look at is your speed sensor.
These parts send information to your computer for shift comands. SCWrench

[RBris66]

I have had a similar experience with my '96, 5.0L. now 47k. miles. I started
the truck one day and didn't have the gear shift position indicator light... I
shut off the truck and restarted, now I had a light but the Service engine soon
light came on and it shifted VERY hard. When I returned home, I cleared the
code in the computer by removing the battery cable for a minute or two and it
has not happened again. Hope you get it figured out.

Rick
RBr...@aol.com
1996 Chevy C1500 Ext cab
1966 Chevy C10 stepside

[nt]

Hmm.

Sounds like something is causing the tranny to thump into gear too quick. It
doesnt make sense something is slipping if it's thunking into gear like that,
although it's possible.

Check the throttle and make sure the linkage (or electroic sensor, im not too
familiar with these trucks) is OK and you're fluid is a good color

Other than that, try a new dealer. This dude must be a MORON if he cant figure
out what a code means.. Chevy should have a tech support line they can call to
find out directly from the manufacturer.

-Nate