ok now im getting a p1870 code. what does this mean and how do i fix it. thanks

 

P1870 means that something in the transmission is slipping. Here's a link to the diagnostic flow chart: https://blazerforum.com/forum/diagno...plained-18227/ The most common problem is either a faulty Torque Converter Clutch, (TCC) solenoid, or a faulty TCC Pulse Width Modulation, (PWM) solenoid. The solenoids are attached to the valve body and requires removal of the transmission oil pan to service them.

 

ok im still getting the po1870 code here are the things i have done.

TCC Regulator Valve Kit, 97 & Up EC3 Units 77754-04K

TCC Apply Valve, Aluminum with Teflon Seal (4L60-E, PWM only) 77805E-K

Oversized Pressure Regulator Valve Kit 77917-07

tranny fluid changed with new everytime the pan came off.

around 35-40 mph the rpm needle flucuates about 200rpm up and down. and the bravada feels like your goin back and forth. then if you give it gas it quits till your cruising around 35-40mph then starts slipping i guess. or from what ive read the torque converter isnt staying locked up. falling out of lockup. still about 2100-2200 rpm at 55 drop it into 3rd and the rpm goes 3000rpm then back to overdrive and then 21-2200rpm.

so what do you guys think it is.

 

You didn't follow the flow chart for P1870 or you would have found the problem Did you replace the TCC solenoid, and/or the TCC Pulse Width Modulation, (PWM) solenoid while you were in there? If the valves were sticking, it would cause screwy shifts, but if a solenoid is working intermittently, the torque converter will not stay engaged. Depending on the axle ratio, it should run around 2000 RPM at 70 MPH.

 

well im not acutally doing this myself. ive been taking it to a transmission shop. and he says that when it slips it looses all or most of the line pressure at once. he says that the case or something in there is cracked allowing the pressure to drop.

and some more details of what its doing....

ok when going between 35-40mph in overdrive when you step on the gas a tiny bit or let off the gas a bit the rpms start going back and forth and the truck goes gack and forth. but if i step on the gas a little more it will quit or if i SHIFT it into 3 then it will stop.

i can drive it all day in 3 and NOT a single problem. but in overdrive it will slip between 35-40mph.

now ive been thinking that when i changed the pan gasket since it was leaking... i used a pick to get the seal out of the valve body where the filter goes into... and i think when doing so i might have slipped and hit one of the 1-2 or 3-4 shift solenoids.

can a cracked 3-4 shift solenoid be causing the p1870 code?

it all started when i changed the filter/ fluid/ gasket.

thanks for the help

 

There are 6 solenoids in your transmission, 3 of which only affect the torque converter. If it doesn't act up when you manually put the shifter in 3, in other words, upshifts and downshifts normally from 1-2, 2-3 and 3-2, 2-1, and only has a problem in OD, I would strongly suspect a TCC solenoid or PWM solenoid, or a poor connection, (loose wire) to them. Make sure you check the connector at the right front corner of the trans case where all of the solenoid wiring goes into the pan area. It's not very common to develop a loose connection there, but it can happen.

 

ok well the mechanic i took it to hooked it up to his computer and says that all the solenoids are working like they should when they should. but the pressure drops to almost zero when it starts to slip. he doesnt know what to do and im also stumped. he replaced all the parts in the sonnax book hes got that fixes the 1870 code but still no luck.

what could this be?
thanks again