4l60e PWM mod information

cornchip

Original poster
Member
Jan 6, 2013
637
I see I may have to pursue this and thought I'd see if I got it right. In OD I get P0894 whenever I drive highway and the PCM commands lockup of the converter. I feel that just being in 4th and having no lockup, things would be just fine and the transmission temps would stay down. With the temps up after a run in 4th with lockup, I get the harsh 1-2 shift afterwards. I tried just 3rd over the same course, and had no harsh 1-2 bump shift when I got off the highway. Control the temps by avoiding lock up, and I reason I should be able to drive in OD with an unlocked TC and still maintain better transmission temps along with avoiding the damage the slippage must obvously be causing. Do I have that right?

So the PWM mod from searching around shows the PWM solenoid installed without the O-ring and end filed down some to allow the transmission to bypass and effectively build no pressure to the TC lockup. Is there side effect to this over the long haul such as the pump being robbed of capacity due the very large internal leak we have effectively made? Is removing the PCM control ground an alternate way of accomplishing the same ting? I'm positive the PCM won't be happy either way when it fails to lock the TC or see the ground resulting in a check engine light. I'd like to hear back long term experience from anybody here who has tried or currently still uses this mod.

Cornchip.
 

Mounce

Member
Mar 29, 2014
13,667
Tuscaloosa, AL
First I've heard about modifying it in this fashion. I've only heard of the upgraded solenoid that makes it go from unlocked to locked instantly instead of slipping into lockup (pwm slowly applying the lockup).

However there are many members more versed in trans mods than I am so they'll probably help more than I.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
We usually do the shift kit method of eliminating the PWM for full engagement. You want to eliminate TC lockup completely? Dunno if that would work because you may still get the code.
 

Sparky

Member
Dec 4, 2011
12,927
You've actually got it backwards. If you eliminate TC lockup so that the converter never locks, you're going to send transmission temperatures way high, still get those harsh 1-2 bangs, and burn stuff up. Not a good idea. The losses in the torque converter while it is not locked up is a big source of the heat increase, not to mention also reducing your mpg.

Do what I did to fix this issue on my old car. Not really surprised you haven't seen P1870 yet because it seems like it takes a lot for it to finally throw it, but this will fix the TCC lockup issues.

https://gmtnation.com/forums/threads/4l60e-valve-body-upgrade-kit-aka-p1870-code-buster.17234/
 

cornchip

Original poster
Member
Jan 6, 2013
637
Yes...last August I had both 1870 and 894 at the same time while towing in OD. Hasn't been right since. What sucks is I have a 14 hour tow from Northern Wisconsin to Southern Ontario planned in the next 6 weeks or so. I need to get this sorted out soon. Trailer weight won't be more than 2000lbs, the the boat will be draggy as shit. I'm sticking to 60mph in 3rd all the way back, but going there I will be without a trailer. I don't plan on going slow and wan't OD.
 

Sparky

Member
Dec 4, 2011
12,927
Do the shift kit and throw an aux trans cooler on there. You'd be golden then.
 

cornchip

Original poster
Member
Jan 6, 2013
637
This looks like it can be done in the truck. I assume this is how it's done.
 

Sparky

Member
Dec 4, 2011
12,927
Yep. Just a pan drop, valve body drop. The servo on the side is a bit of a bear to get to (lower the crossmember a bit to help, and a good large prybar to push the cover is necessary).
 
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cornchip

Original poster
Member
Jan 6, 2013
637
Thanks Sparky, I'm going to set this in motion and jump in. It's honestly one of those jobs I just always wanted to avoid.


3/20/18 - Kit ordered.
 
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cornchip

Original poster
Member
Jan 6, 2013
637
Had about the best weather we've had in weeks to do some wrenching on the 4L60e. I had mixed results but had a backup plan with a good valve body pull to mod and leave my original alone should I need to restore my prior configuration. First I did the easy thing and put in the largest B&M cooler I could stuff in. Went well. Second I did the vette servo. Lowered the cross member down 2 inches, it's a must do to gain any access to the side of the transmission. I machined a plate and bought a tire spoon to compress the servo cover while giving me two hands to install the wire retainer. A note, listen for the 'snap' of the ring when seating it....work it to depth at the slots. Lastly the valve body where this went a little wrong. I built the pulled valve body to the constructions as best as I could figure. I didn't have any doubts as it seems logical. However once installed I couldn't shift out of second. I reverted back to the stock valve body and all seems as it was. The check is back with the P0894 this morning.
 

Sparky

Member
Dec 4, 2011
12,927
Was it a similar year range valve body? Because there were some changes made to them.
 
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cornchip

Original poster
Member
Jan 6, 2013
637
Was it a similar year range valve body? Because there were some changes made to them

My 07 has a build of June 07 and the core is from a Jan 07. Casting #s were the same and visually identical....as best I could say. There are a few valves untouched during the kit that I can't vouch for that may be different internally with regard to springs. The rest of the kit made good sense. Glad I had a way back. Still might not be done with it for now. I'll tell ya, it's a mighty bad feeling when stuff's going sideways while messing with that shit. Happy it's no worse for the wear.
 

Sparky

Member
Dec 4, 2011
12,927
Would it go into 2nd if you manually shifted to 2nd?

A common thing that prevents stuff from shifting is if a bolt was in the wrong place (long bolt in a short bolt hole locking something out for example).

I guess the other thing you could do easily while you have it out is just double check your work, and test the shift solenoids to make sure they operate.
 

cornchip

Original poster
Member
Jan 6, 2013
637
Reverse,first and second were all I had. Wouldn't shift out of second, just kept revving higher. No codes to suggest a non working solenoid (with more time I could have used the TECH 2 to verify). Also the bolts were carefully removed and replaced in there rightful places. The instructions have a great description of bolt length to prevent locking of the center section.

I might revisit this later and rebuild the ISO CONV valve....although it showed no signs of visible wear. Impressed with how clean both my own and the wrecker 4l60e were when I opened them up (both have the same approx mileage at 160km's). Still driving fine as of today....and I'll swear the vette servo has improved the shift quality over all.
 

Sparky

Member
Dec 4, 2011
12,927
Oh gotcha, I misunderstood.

You won't get codes right away on the solenoid, necessarily. It may take the computer a moment to figure out something isn't shifting right.

I'd still go back over everything and make sure the various parts are in their bores correctly. All it really would take is one spring or piece to be pinned in the wrong slot by accident and even if electrically all is OK it won't shift to 3rd. I almost put one of those pins in the wrong place before. Not sure what the effects would have been.
 

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