Code 1870, on a 96 Impala SS


Gone In Sixty
While driving home the other day my check engine light came on, so yesterday i stop at Autozone to receive the code, which was a code 1870, they said it had something to do with the transmission, what do i need to check?
The 1870 code is set when your TCC or other clutches slip. This isn't good. There can be many causes. Weak solenoids, bad O rings or seals, band slip, stuck valves, or simply the fact that your TC is a high stall and is affecting the computer just to name a few. I would call Mike at PMAC and talk to him about it. Since he built it, I say he would be best informed to deal with it.

What does your fluid look and smell like?
PMAC did not build this one, i bought this one from the GM dealer about 3yrs ago....I check the t/m fluid and it was clear colored no burn smell..the engine light has what?
Oh, I looked at your sig and thought you were talking about that car.

What TC are you running in your current set up?
Every thing is stock, this car does not get driven hard...but it seems to shift ok......but i didnt know that a check engine light would come on for the transmision
My computer crashed before I could delete my dumb question. Duh,the car in question was what the title said it was....ok...clear head...ok, I'm on track again :) Yes you can get codes like this. In a 5.7liter 4L60E configuration that code means you are slipping somewhere. Could be clutches and it could be TCC. What were you doing when the code came up? Was your tranny feeling any different?
Only thing i did different that day was i had to stop real quick because some one pulled in front of me... then when i got home the check engine light was on, but when i pulled in the driveway the car did down shift kinda hard, but that was the only time it did that...
This was very common on pre-98 model year vehicles with the 4L60E. Starting with the 98 model year, GM changed the parameters with which a code 1870 would appear.
I cant tell you how many transmissions in Astro vans and S10's were replaced because of this. Sad, but true.
Brian; Is there anyway the older pcms could be reflashed to change this?
If the code reads 1870 what does it mean? anybody have a code book for this? I`m not familar with this car yet, i had it for a while but never worked on it
The tranny's on impala's are infamous for going bad. Usually it's the clutch paks that go bad first(when your unmodded). Or the solenoid. If the fluid seems fine and everything is working well, It could be the computer. There kinda funny, I got false codes a few times before swapping to obd-1. It is unlikely your that lucky, but you wouldn't be the first
The 96 model year was/is famous for this code.

The valve body is made of aluminum and it wears. If that is the cause of the 1870 the choices are replace the valve body or try and repair it with the sonnax repair kit.

I've never personally tried that kit, just seen it listed in the catalogue.

When does the code set? The 1870 sets whenever the pcm detects any sort of slipage in the tranny, TCC, clutches, whatever.

Chances are yours sets after a bit of a steady state highway cruise right?

Don't let this go on too long. When the 1870 is set max line pressure is commanded and sunshells tend to break as a result.

I'm not sure if there is a reflash available for this on your vehicle. Send me the VIN # and I'll see if there is one listed or not.


Your right i only use this car to drive to work, 1hr drive (oneway) at 80mph all the way or 90-95mph when late, my vin# 1G1BL52P5TR143347, DO I NEED TO GET A NEW TRANSMISSION OR WHATS NEXT? Is it a matter of time before it goes? i bought this transmission new about 3yrs ago less than 80,000 on it , the car has 135,000 now.....