P1870, 4L60E, PWM delete etc.

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Peavey

Newbie
Joined
May 21, 2022
Messages
20
Reaction score
20
Location
Sweden
Hi everyone!

Got a 1997 GMC Savana 1500 with L31/4L60E approaching 150K miles. At one point last summer (the rig is mainly used as a vacation-vehicle for me and the family) when driving home from our holiday, the gearbox started to shift really hard between 1-2 and I lost the lockup. This was after a few hours of driving on a hot day with the van fully loaded. We pulled over, read the codes and it was the infamous P1870. After like an hour, we took off again and the code and hard shifts were all gone and lockup had returned as well. Managed to drive another 3 hours without any further hassle and it has not returned since then, though it has not been driven any long distances either.

So, I´ve read both on this forum and elsewere that this is more or less typical for the 4L60E and that the cure is to install some sort of PWM delete/block off valve instead of the OEM version.

If I were to buy a Fitzall valve like the one suggested in the very informative thread by @NickTransmissions, is it possible to install this without removing the valve body ? I´ve seen some clip on youtube saying it is possible with a bit of fiddling, but what do you guys on this forum say? The reason I´m asking is that I´m fairly experienced with mechanical work but have only done fluid and filter changes as far as transmissions are concerned, so I´m not sure whether i would be able to pull it off if the valve body has to come out.

Aside from changing the valve, is there anything else you think be worth replacing "while in there"? The transmissions shifts fine in my opinion and the oil seems to have normal red color without any funky stuff on the dipstick.

Are there any negative aspects of deleting the PWM as far as transmission durability goes? I´ve read on Sonnax´s website that it puts stress on different transmission components and that they recommend to use their solution, but it requires more tools and, not to say the least, more money.

Sorry for all the questions, but like I wrote, this is a bit uncharted territory for me and there aren´t many US transmission specialists close to where I live (middle part of Sweden). Any help or advice would be appreciated.

Thank you!

//J
 

NickTransmissions

Supporting Member
Supporting Member
Joined
Aug 16, 2023
Messages
810
Reaction score
1,214
Location
Las Vegas
Hi everyone!

Got a 1997 GMC Savana 1500 with L31/4L60E approaching 150K miles. At one point last summer (the rig is mainly used as a vacation-vehicle for me and the family) when driving home from our holiday, the gearbox started to shift really hard between 1-2 and I lost the lockup. This was after a few hours of driving on a hot day with the van fully loaded. We pulled over, read the codes and it was the infamous P1870. After like an hour, we took off again and the code and hard shifts were all gone and lockup had returned as well. Managed to drive another 3 hours without any further hassle and it has not returned since then, though it has not been driven any long distances either.

So, I´ve read both on this forum and elsewere that this is more or less typical for the 4L60E and that the cure is to install some sort of PWM delete/block off valve instead of the OEM version.

If I were to buy a Fitzall valve like the one suggested in the very informative thread by @NickTransmissions, is it possible to install this without removing the valve body ? I´ve seen some clip on youtube saying it is possible with a bit of fiddling, but what do you guys on this forum say? The reason I´m asking is that I´m fairly experienced with mechanical work but have only done fluid and filter changes as far as transmissions are concerned, so I´m not sure whether i would be able to pull it off if the valve body has to come out.

Aside from changing the valve, is there anything else you think be worth replacing "while in there"? The transmissions shifts fine in my opinion and the oil seems to have normal red color without any funky stuff on the dipstick.

Are there any negative aspects of deleting the PWM as far as transmission durability goes? I´ve read on Sonnax´s website that it puts stress on different transmission components and that they recommend to use their solution, but it requires more tools and, not to say the least, more money.

Sorry for all the questions, but like I wrote, this is a bit uncharted territory for me and there aren´t many US transmission specialists close to where I live (middle part of Sweden). Any help or advice would be appreciated.

Thank you!

//J
There's a guy on Youtube that shows you how to remove the retainer clip and extract that valve without dropping the valve body; you can search 4L60E TCC PWM Valve Body Removal Not Necessary or some variation thereof...The Fitzall valve is designed to do two things: 1) mechanically convert the TCC regulatory apply from a pulse width modulated pattern to a simple 'on/off'; this reduces the designed in slip that comes with that mode of application. 2) Seal off an otherwise excessively worn bore to eliminate excessive TCC slippage, resolve DTC P1870 (or P0894 in later units) without having to either ream the bore for an oversized valve/sleeve kit or replace the valve body all together.

I've heard mixed things about the Fitzall valves; some of us swear by them while others won't use them, citing Sonnax's advice about extra stress on the converter, etc. I have used them in numerous 4L60Es over the years and never had one come back due to that valve causing damage but I'm just one builder, perhaps others' experiences are different.

If you are concerned about using the Fitzall valve but otherwise want to address a problem with the TCC regulator valve/circuit, you can always install the Transgo SK4L60E shift kit as it contains a .001 oversized valve and spring that restores a mild to moderately worn bore to factory spec and doesn't convert the PWM to a 100% on-off but still reduces designed-in slip.
 

Peavey

Newbie
Joined
May 21, 2022
Messages
20
Reaction score
20
Location
Sweden
Hi!

Thank very much for your reply and info! I´ve had a look at the Transgo kit too. I suppose installing it both requiers the valve body to come off as well as (maybe?) being more experienced on working on transmissions but I may be very well be wrong. Maybe it´s a dumb question but would you say that the Transgo kit has more advantages, aside from the installation process, over just installing the Fitzall valve when it comes to the longevity of the transmission?

Thanks again!

//J
 

NickTransmissions

Supporting Member
Supporting Member
Joined
Aug 16, 2023
Messages
810
Reaction score
1,214
Location
Las Vegas
Hi!

Thank very much for your reply and info! I´ve had a look at the Transgo kit too. I suppose installing it both requiers the valve body to come off as well as (maybe?) being more experienced on working on transmissions but I may be very well be wrong. Maybe it´s a dumb question but would you say that the Transgo kit has more advantages, aside from the installation process, over just installing the Fitzall valve when it comes to the longevity of the transmission?

Thanks again!

//J

You're welcome, J.

I'd install the transgo shift kit...It's not difficult at all plus Transgo's instructions (at least for that kit) are very easy to follow, clear and give you all the guidance you need when doing the work. The shift kit will correct more than just a potentially leaky TCC regulator valve...It will also smooth out your 1-2, 2-3 and 3-2 down shifting, provide for better apply and release characteristics during shifts and provide for better band longevity.

If you're at all mechanically inclined, you can install this kit...The only tools you need would be a series of picks, small flat blade screw driver, pencil magnet (maybe), paper clip to unfold and shape as need to get stubborn valves out, inch lb torque wrench for fasteners (all get 98-104 in lbs, except the 8mm bolts that hold the fwd accumulator cover and EPC retainer clip in place - I use 85 in lbs for those).

If you get stuck or to prepare, you can watch my Transgo HD2 shift kit install on Youtube. It follows the exact same procedures with the exact same parts as the basic kit, except for the little purple spring that the HD2 kit has for the 3-2 downshift valve (you can still block that valve inboard, just find something that works, but this mod is not needed on daily driver/stock applications).

Quote my post here w/any questions, otherwise I won't see your reply right away.
 

1998_K1500_Sub

Nitro Junkie
Supporting Member
Joined
Jan 28, 2019
Messages
2,417
Reaction score
3,685
Location
Rural Illinois
Can the "PWM delete" be effected with a "tune" to the ECU? The ECU controls this behavior, so it would seem possible / likely.

I would much rather do this on the computer than on my back.

I haven't looked at the transmission parameters for the ECU on my '98 for this parameter, yet; this thought just came to my mind so I posted it.

(@NickTransmissions, nice write-up in the prior post :waytogo: )
 
Last edited:

Peavey

Newbie
Joined
May 21, 2022
Messages
20
Reaction score
20
Location
Sweden
You're welcome, J.

I'd install the transgo shift kit...It's not difficult at all plus Transgo's instructions (at least for that kit) are very easy to follow, clear and give you all the guidance you need when doing the work. The shift kit will correct more than just a potentially leaky TCC regulator valve...It will also smooth out your 1-2, 2-3 and 3-2 down shifting, provide for better apply and release characteristics during shifts and provide for better band longevity.

If you're at all mechanically inclined, you can install this kit...The only tools you need would be a series of picks, small flat blade screw driver, pencil magnet (maybe), paper clip to unfold and shape as need to get stubborn valves out, inch lb torque wrench for fasteners (all get 98-104 in lbs, except the 8mm bolts that hold the fwd accumulator cover and EPC retainer clip in place - I use 85 in lbs for those).

If you get stuck or to prepare, you can watch my Transgo HD2 shift kit install on Youtube. It follows the exact same procedures with the exact same parts as the basic kit, except for the little purple spring that the HD2 kit has for the 3-2 downshift valve (you can still block that valve inboard, just find something that works, but this mod is not needed on daily driver/stock applications).

Quote my post here w/any questions, otherwise I won't see your reply right away.
Hi again and thank you once more for a really good answer, appreciate it!

Allright, maybe I´ll give the Transgo kit a go after all. If I were to tackle this, would you say that i would be necessary (or at least good practice/make sense) to replace shift solenoids and other electrical bits as well or is it just money down the drain in an old transmission like mine?

Best regards

Johan
 

NickTransmissions

Supporting Member
Supporting Member
Joined
Aug 16, 2023
Messages
810
Reaction score
1,214
Location
Las Vegas
Hi again and thank you once more for a really good answer, appreciate it!

Allright, maybe I´ll give the Transgo kit a go after all. If I were to tackle this, would you say that i would be necessary (or at least good practice/make sense) to replace shift solenoids and other electrical bits as well or is it just money down the drain in an old transmission like mine?

Best regards

Johan
Id replace them, if you can swing it...they are an 80-100k maintenance item so if they've never been replaced, now would be the time to do so.
 

Peavey

Newbie
Joined
May 21, 2022
Messages
20
Reaction score
20
Location
Sweden
Id replace them, if you can swing it...they are an 80-100k maintenance item so if they've never been replaced, now would be the time to do so.
Allright, the solenoids are probably past their "expiration date" by now then, so I may as well replace them also. I don´t really know if they, or the transmission, have been replaced sometime in the past but everything seems to be original by the looks of it. Rockauto, which is where I usually go to for parts, seems to provide the Transgo kit, and some of the solenoids are sold individually, but I can´t seem to find a kit which includes all of them and/or a wiring harness.

I suppose that it´s AC Delco/GM Genuine I should be looking for? Do you by any chance know any other reputable transmission parts supplier who sells these (or another quality brand you know) solenoid kits/harnesses? I´m pretty much bound to shop online since the market for US car parts in Sweden is pretty limited and, not to say the least, quite pricey compared to shopping from over the pond. There´s always Ebay but when it comes to more specific items like these, my gut tells me that it´s better to pay a little more just to be sure that you are actually getting the correct stuff.

Thanks again!

//Johan
 

Deancr11

I'm Awesome
Joined
Sep 29, 2020
Messages
125
Reaction score
219
Location
Texas
Global transmission parts, Oregon performance transmission, and transtar transmission. I've done business with all 3 with out any problems. They should have what you want.
 

NickTransmissions

Supporting Member
Supporting Member
Joined
Aug 16, 2023
Messages
810
Reaction score
1,214
Location
Las Vegas
Allright, the solenoids are probably past their "expiration date" by now then, so I may as well replace them also. I don´t really know if they, or the transmission, have been replaced sometime in the past but everything seems to be original by the looks of it. Rockauto, which is where I usually go to for parts, seems to provide the Transgo kit, and some of the solenoids are sold individually, but I can´t seem to find a kit which includes all of them and/or a wiring harness.

I suppose that it´s AC Delco/GM Genuine I should be looking for? Do you by any chance know any other reputable transmission parts supplier who sells these (or another quality brand you know) solenoid kits/harnesses? I´m pretty much bound to shop online since the market for US car parts in Sweden is pretty limited and, not to say the least, quite pricey compared to shopping from over the pond. There´s always Ebay but when it comes to more specific items like these, my gut tells me that it´s better to pay a little more just to be sure that you are actually getting the correct stuff.

Thanks again!

//Johan
AC Delco, Borg Warner or Rostra.

AC Delco for the shift solenoids and pressure switch manifold

Borg Warner for the electronic pressure control solenoid (sometimes listed as a "force motor")

Rostra for the wiring harness, 3-2 control solenoid and PWM solenoid.

In addition to the online retailers @Deancr11 provided, Cobra Transmission and Transpartswarehouse.com should also have what you need and ship overseas.
 
Top