Buick Century P1870

[jmgtp]

long long time without posting...

This is a for a friends car that I told him I would look at while he was out of the country.
The check engine light is on and my obd II scanner indicates p1870 which from a bit of googling appears to be a transmission slippage code.

The car is a 97 Buick Century, 3100, 4t60e, ~120k.

It runs and drives perfectly. He thinks his gas mileage may have gone down a bit in the past year or so. He claims around 25 mpg with a mix of city/highway - I think thats pretty good!

Since the car drives perfectly the only thing I can think of is the tcc not locking? It runs so quiet, shifts so smooth and doesn't have a tach so I'm not sure if I would be able to listen/feel for tcc lockup. Doesn't the 4t60e have some kind of known problem with the tcc? I thought it was that it wouldn't unlock or lock at inappropriate times causing a stall.

Any ideas? I can take it for a ride and try to listen/feel for it - but I've never owned an auto car so I don't really know what I'm looking for. What engine temps, speed, etc should I be at before the tcc would engage? Say the tcc is bad what kind of job is it to fix? Trans drop? He's considering a new car in the next few months and wouldn't want to drop a lot of cash or a lot of my time on fixing it. The car runs/drives perfect, doesn't stall or make noises. When he said gas mileage and CEL I thought this would be a simple o2 sensor issue!

[IanSzgatti]

I'm a member of IATN, so i dug this up out of the archives for you. Three possible problems here... none to easy without a technician to diagnose.. good luck



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Rating:
Status: Closed w/Summary
Comments: No Comments
Replies: 5 (View Replies)
From: Travis Dewitz
Date: May 13, 2005 12:09 PM

REPLY: Click here to reply to this SUMMARY!

1997 Buick LeSabre

Engine: 3.8 L / 231 CID / 6 cyl / Gas / OHV
Fuel: Fuel Injection
Ignition: Distributorless
Trans: 4-speed Automatic Transaxle (Electronic)
Mileage: 98,000 mi
VIN: 1G4HR52K2V

Misc Data: 4t60e
Affected Item: tcc lockup
Condition: no lockup
More Info: Repair history included below

_____________________ ORIGINAL MESSAGE _____________________

Have a car here that has no tcc lockup. I am getting code
p1870. First time I fixed the car the complaint was that it
surges driving up hills. Well with the tech 2 I could command
tcc lockup 99% and problem gone. I know gm has the valve body
problem so we pulled tranny had it look at and had the sonnex
tcc kit installed. 2 weeks later light was on with p1870.
Checked tranny and now it is commanded 99% and no lock up.
Pulled trans and had him go through it. He found nothing wrong
but still replaced pwm and tcc solenoids. Everything is
suppose to be in order. He said him and the other tech tripled
checked everything. Installed tranny with another new
convertor. Carbon woven one. Problem still no lock up. When
road testing evrything is operating normal besides that the
pwm always climbs to 99% since it can't control slip rpm. slip
rpm runs about 200-800 rpm. I can command tcc to lock and
unlock and there is nothing there. All pressures from mainline
are within spec. I amp probed tcc sol. and pwm. Both are
operating just as scan tool shows. All I can guess is that
something happened when rebuilt, but what. Lock up worked
before but it surged most likely from fluid bypassing. So I am
down to internall hyd. issue or bad convertor. Unlikely for 2
new convertors to be bad. trans tech claims everything was
tripled check and good internal? Any help needed. Thanks to
all of you.

RELATED REPAIR HISTORY

transmission rebuilt and sonnex kit installed.

__________________________ SUMMARY__________________________

After a lot of searching and some good replys from others, we
definintly have something wrong in the valve body. When the
customer brings back the car we will have to pull the trans
again. Most likely we will be getting a new valve body for it.
One good post said that maybe a bolt that is a hair longer may
be blocking a passage? Our trans rebuilder found a bullentin
from sunnex that says that the gm valve body and a certified
rebuilt trans. valve body have a different sized passage where
the tcc valve is. He thinks because of this he may have
overdrilled the bore if it was the certified valve body which
can also come on new transmissions. When I find out what
happended I will update for you. Thanks again.


Travis Dewitz
Technician/Manager
Dewitz Truck & Auto Repair
Eau Claire, Wisconsin, USA

iATN Technician Sponsor

REPLY: Click here to reply to this SUMMARY!

[jmgtp]

Thanks for the reply. I'm not too sure what to make of it! haha. I've never owned an auto trans car and don't know much about an auto trans. Seems like what you have there is someone with a driveability issue though, and this car doesn't have one. If that light wasn't on you'd never know there was something wrong. If I have time tomorrow I'm going to drive the car a bit and see if I can feel the tcc lock - that would be step 1 at least. I don't want to pull the trans on this thing, I just don't have the time and it wouldn't be worth it since this car is soon to be replaced. I'm willing to go about as far as checking the solenoid for the tcc, externally accessible?

[IanSzgatti]

you just said you dont even know what to look for, so dont say you have no driveability problem without really knowing... if that code has been set, believe me, you will find something.

[3400-95-Modified]

With that code set it will never lock the TCC it disables it... It may be the TCC clutch that was slipping in the converter that caused the code.

Now did he ever change the gear ratio of the car some how? I know when I took my beretta and went to OBDII, (as obdI.5 i didn't care) the ratio had been changed from 2.97 to 3.33 and when I was driving on the highway it saw the higher RPM per MPH as a slip and would throw that code. I had to edit the drive sprocket ratio setting in the ECM to make it realize the change so it would ignore the higher RPM.

If it hasn't been touched then I'm going to say yes, 4th gear may have been slipping which would throw that code, and high mileage 4t60e's are known to cook 4th gear with how loose it flops into it.