P1870 Hard1-2 Shift....please help

[83cutlass]

Here's my experience with this DTC 1870 on my '95 blazer. So my truck had that code and the previous owner just drove it for a while until the 3-4 clutch burnt up and the trans no longer had 3rd or 4th gear. So they gave me the blazer for free and I rebuilt the transmission. I drove it and knew the converter wasn't locking up when the trans was warmed up and I was right when that 1870 dtc came back a short time later. So I ended up replacing the valve body and now the problem is solved. Hopefully you'll find this story helpful.

[woogexx]

Originally Posted by MT-2500

Here is a quote from one of the top transmission men.


In a nutshell, the valve body does chronically wear in the 4L60E especially in the lockup PWM bore. The code lights when there is more then 100 rpm or so when locked up. Depending on mileage and fluid condition will determine the next course of action. The seal on the input shaft gets tons of heat and is the most critical seal in the trans. If there are high miles, usually what it takes to wear the vb, then the rubber seals as well as the Teflon ones are just as worn. The 1870 code is telling me there is a internal leak in this trans...someplace. The transmission is a multitude of leaks and it is engineered that way, some are good leaks because they lube planetaries and some are not so good because they make the pump work harder to make up for the leaks inside. Teflon rings leak to get enough holding power to not leak. The point here is if you have excessive or extra leaks then the PWM must cycle higher pressure and volumes to compensate making it work harder and the very forces that wear out the vb bore are increased wearing the bore quicker. In addition to that factor, with internal leaks you also have increased temperature and heat kills big time in a tranny plus it decays the additives in the fluid itself and now you are in a downhill spiral as the trans self destructs form leaks and heat and destruction of the fluid itself. Now the hard parts will start to wear at an increased speed, the pump is trying to maintain for the fluid loss(leaks), the planets will start overheating as the bushings wear out you generate more hemorrhaging and more damage.
Yes, at that point the vb is a bandaid, it may solve the problem for now but the internal wear and hardening of the seals is still there and will continue to wear. The problem I have with just throwing a vb at this problem is simply, the worn components will make the new vb work harder and cycle more than it should and the consequence of that is another prematurely worn out vb and ultimately overhaul of the trans that you should have taken care of before. The transmission is a complete and interdependent unit meaning all parts rely and interact on each other. If one part is worn out then you must deal with the unit on the whole. There are exceptions to every rule and the jeep is a good one, the accumulator plate is held down by too few screws and the plate is under enough pressure that when the screws break, the plate peels back like a lid on a dog food can. If caught soon enough then a repair of the valve body is sufficient to be a complete repair. If you have a 4L60E with 100k on it and smokey fluid and only a P1870 then you are not doing the customer a service by simply replacing the vb.
I have yet to take a trans apart that was simply coding 1870 and not found hard seals or other problems internally. Most of the time, I have not even needed to deal with the vb at all, aside from basic clean up and solenoid replacements. I have had to replace more transfer plates than valve bodies from the balls eating through. In the past 6 months, I have replace 2 valve bodies. I do not use the sonnex kit although the place I get my vb's from does.
I hope this helped you understand why I claim the 1870 code means internal problems more than just throwing a vb in my experience.

alright, well thank you....that was kind of depressing advice. Kinda made me loose hope. I guess Ill just get it scanned at a transmission shop. All theyre gunna say is "yeah you need this, you need that....its gonna be 1800"
I might just get the shift kit, get it installed. Drive it till it is no-more.

[woogexx]

Originally Posted by 83cutlass

Here's my experience with this DTC 1870 on my '95 blazer. So my truck had that code and the previous owner just drove it for a while until the 3-4 clutch burnt up and the trans no longer had 3rd or 4th gear. So they gave me the blazer for free and I rebuilt the transmission. I drove it and knew the converter wasn't locking up when the trans was warmed up and I was right when that 1870 dtc came back a short time later. So I ended up replacing the valve body and now the problem is solved. Hopefully you'll find this story helpful.

That was my initial thought on repairing. What I was going to do. Replace the valve body. But I get so many conflicting answers from people all the time, online and not. That Im kinda if'y. So Im just going to start from square one again I guess and get it tested. If the problem is too expensive and the kit will work for the time being...well then....put that baby in.

[MT-2500]

Originally Posted by woogexx

alright, well thank you....that was kind of depressing advice. Kinda made me loose hope. I guess Ill just get it scanned at a transmission shop. All theyre gunna say is "yeah you need this, you need that....its gonna be 1800"
I might just get the shift kit, get it installed. Drive it till it is no-more.

Glad to see you weighing all of the facts and pros and cons on it.
Yes find a good honest repair shop and get it checked out.
May be a minor or major problem.
Some transmission chain stores are a little rebuild happie.
Which ever way you go.
And let us know how it goes.
Good Luck
MT

[arlonadkinson]

If you like go ahead and let someone sell and replace your transmission but here is my suggestion! Check around and see if you can find a minor vacuum leak! This can simply be the big round hose that goes from the fuel injection to the power brake hub! This is normally a push in connector which has about a 1/2 inch hose clamped on it! If there is any kink or the connector is not in correctly a leak will occur and the transmission will shift rough as though you will be thrown out of the vehicle! Try unplugging this connector and plug it back in hard and straight and maybe you will be lucky and fix your problem. If the vacuum is correct your transmission will shift better than you have ever experienced!

[st8542]

Yes i too have had the p1870 code. drove mine for 20,000 miles of rough shifts. a friend told me to have the valve body reamed and a sleeve put in. which they did and the mechanic said i was VERY LUCKY to have made it this long. i have driven for 1000 miles now and all is well. i now get 22 mpg hwy compared to 19 - 20 before.

[MT-2500]

Originally Posted by st8542

Yes i too have had the p1870 code. drove mine for 20,000 miles of rough shifts. a friend told me to have the valve body reamed and a sleeve put in. which they did and the mechanic said i was VERY LUCKY to have made it this long. i have driven for 1000 miles now and all is well. i now get 22 mpg hwy compared to 19 - 20 before.

This post is old and dead.
Always check date on a post and if old.
Let the dead rest in peace.
The valve body repair is only for certian years.
But a code 1870 almost always goes back and come back to internal transmission pressure leakage.
transmission trying to overcome pressure /lose or leakeage is what causes the valve body to wear out.

[blazes9395]

Now I know that this is old, but I have read this over and didn't realize the dates, but I thought I'd add some info on here, in case anyone is searching the P1870 code. The P1870 is a trans componenent slipping, it doesn't give a specific part problem, and can literally be many different things. That said though, usually, in my experience, the problem can be traced to either the torque convertor itself, or the circuit that controls lock-up, in this case, as was said in an earlier post, the TCC Regulator Valve and/or PWM solonoid.

The 4L60E from '95 and up had a controlled, gradual torque convertor lock-up, not the on and off lock-up found in earlier versions. When the convertor is signaled by the PCM to begin lock-up, this is done in percentages, all the way to complete lock-up. The PCM monitors lockup by sensing the different speeds the engine is turning, as to what the drive shaft is turning, this difference in speed is what the PCM keeps track of. If they are too far off and are out of range thats when the P1870 comes up, as slippage, or too big a difference in speeds between the engine and transmission is sensed, and in turn the PCM commands max line pressure in an effort to reduce or eliminate the slippage it is sensing. The idea behind this was to try and save the transmission, to limp it home, without overheating it as a result of slippage. Thats why driving a vehicle with a p1870 will usually burn up a trans, because max line pressure puts a lot more stress on the internals, eventually damaging something internally.

All the valve bodies from GM, even the "updated" ones eventually go bad. All GM did to update the valve bodies was by replacing the TCC regulator with a bigger one and reboring the valve body. You can tell if the valve body was a serviced unit as these valve bodies were stamped with "serv" on them. The problem is the valve body is made of aluminum. The valve rubbing on the aluminum valve body wears those spots and causes oil pressure to leak at that point. When the PCM commands the PWM to start ramping up lock-up of the convertor, the TCC regulator cannot be controlled as its leaking to much oil past it, causing the convertor to lock up to slowly, if at all. The PCM sees the difference in speed between the engine and trans and boom your 1870 pops up.

Now if the trans was not run bad and hasn't been driven to long with the P1870 and proper diagnosing leads to the TCC regulator as the possible problem, then usually replacing the valve body or using an aftermarket fix(i always prefer the sonnax update) will get you going again. Shops don't always prefer this route because if they try this and a couple weeks it (the vehicle) comes back again with the same p1870, then its kinda hard to now tell the customer they need to rebuild their trans.

Now again like it was said before, the P1870 can mean a few things, so proper diagnosing is important, but the 4L60E P1870 almost always leads to the convertor, and/or its oil circuit and related parts. Hope this helps someone in figuring out the dreaded P1870.