LS3/4L60e no TCC apply

[trucknut44]

I am working on a 67 Firebird that has had an LS3 and 4L60e swapped in to it. It came to me for some transmission shift point tuning. Upon first test drive, shift points were all very early and no TCC apply. I got all the shift points feeling good, but cannot get the TCC to lock on it's own. I can lock it with the bi-directional controls on the scan tool. I have traced wiring, including the brake switch input, all OK. I compared scan tool data with an older vehicle with a functioning system, the TCC status never changes states, always says OFF. I looked at the OS and I can't find any information on it, it is a T42 controller with OS 24252956. Attached is Rusty 67 Firebird-15.hptthe tune, am I missing something?

[Jon S.]

T42 OS 24252956 was used in 2011 4L65 equipped full-size trucks.

Unplug the round transmission connector from the transmission.

Count the number of pins in the transmission itself (you may need to use a mirror).

Are there 13, 15, or 17 pins ?

[trucknut44]

It has 13 pins. I?m pretty sure he said it was out of a 99-01 Silverado

[Jon S.]

The 13 pin 4L60 was used with Gen 3 (24x) engines, controlled by a PCM (P01 or P59).

With the Gen 4 (58x) engine, GM transitioned to a 15 pin 4L60 (4L65 / 4L70) which added an ISS.

GM later transitioned to a 17 pin 4L60 (4L65) which had both an ISS and an internal Gear Position Switch.

The short answer is - the T42 TCM that you have, will not correctly control the TCC of the older 13 pin 4L60 - due to the missing ISS.

[B52bombardier1]

Do you have the dual circuit brake light switch that controls power to the TCC? PSI Conversions sells one for $23 plus shipping that replaces the single circuit switch installed above your brake pedal. I see that you mention "brake switch input" above . . . just asking.

Rick

[trucknut44]

Ok, thanks. It has the ISS as a selectable parameter, even with that it is not compatible?

[trucknut44]

The brake circuit has two wires, one to the ECM and one to the TCM. The schematics I have found show both of them to be normally open. If I were running a BCM, the switch to it would be normally closed for the cruise control.

[kevin87turbot]

Ok, thanks. It has the ISS as a selectable parameter, even with that it is not compatible?

You can disable the ISS under the Trans diagnostics tab.

[trucknut44]

The ISS has been disabled, and the TCC does not work properly. There are no transmission codes stored.

[Alvin]

The 13 pin 4L60 was used with Gen 3 (24x) engines, controlled by a PCM (P01 or P59).

With the Gen 4 (58x) engine, GM transitioned to a 15 pin 4L60 (4L65 / 4L70) which added an ISS.

GM later transitioned to a 17 pin 4L60 (4L65) which had both an ISS and an internal Gear Position Switch.

The short answer is - the T42 TCM that you have, will not correctly control the TCC of the older 13 pin 4L60 - due to the missing ISS.

This isn't true. 05-06 GTO for instance uses T42 and doesn't have ISS. I think 4 speed Gen 4 vettes also didn't have ISS. I often run 4l60-80's with no ISS without issues on T42's.

OP can see it ask for lockup in the scanner? The stop light wire needs to be hooked up but typically that just causes the TCC to unlock at zero throttle and relock after throttle. Misfire stuff maxed out for a cam?

[trucknut44]

I cannot see it asking for TCC apply. It says OFF all the time. If the OS is for an ?11 Silverado, can an OS change possibly fix the issue? The stop light wire is hooked up correctly. Engine is stock, no misfire modifications are made.

[Alvin]

Even though it's a stock cam I'd try maxing out the misfire stuff just in case.

[trucknut44]

To switch OS, it?s just as easy as finding one that I want on the repository, and programming it into my TCM, correct?

[Jon S.]

This isn't true. 05-06 GTO for instance uses T42 and doesn't have ISS. I think 4 speed Gen 4 vettes also didn't have ISS. I often run 4l60-80's with no ISS without issues on T42's.

OP can see it ask for lockup in the scanner? The stop light wire needs to be hooked up but typically that just causes the TCC to unlock at zero throttle and relock after throttle. Misfire stuff maxed out for a cam?

Hi Alvin - I value your input - but if you read the whole post #4 that I typed - it is true.

He is using a 2011 T42 OS - which will not correctly operate the TCC of a 13 pin 4L60.

Yes, the 2005 and 2006 GTO T42 programming did not have an ISS - and could operate a 13 pin 4L60 - however, it will not communicate with his E38 ECM.

So, back to my original comments - the setup that he has will not work correctly.

I have been down this road many times, but you are welcome to reinvent the wheel if you wish.

[Jon S.]

... I think 4 speed Gen 4 vettes also didn't have ISS. I often run 4l60-80's with no ISS without issues on T42's...

All Gen 4 (58x) Corvette automatics were 6L80 transmissions.

If you are referring to the one year only that the Corvette used a T42 TCM, this was the 2005 E40 Corvette (24x Gen 3 engine). That T42 was programmed without an ISS - but once again, it will not communicate with an E38 ECM.

Some people run the older 13 pin 4L60 in a platform with an E38 ECM. The transmission will shift just fine when controlled by a T42 TCM, however many of these people will not notice that the torque converter does not lockup correctly or consistently.

[Alvin]

I've never heard of a E40 being considered a Gen 3 but I can see your point. I consider it GEN 4 because it shares more tuning wise than with Gen 3.. Anyway..

I routinely... Like several hundred times use specifically GTO T42's OS's in a E67 application with OE ISS to fix a issue specifically with torque converters locking. I also routinely (like several hundred, might be thousands now) use a T42 with no ISS on applications up to 2015 (maybe newer) that doesn't have any issues with TCC locking.

I sell these products... That do not utilize ISS with no issues what so ever.

https://www.pcmofnc.com/product/6l80...ion-harness-3/ <- This product uses a late T42 OS with OE ISS but disabled.

https://www.pcmofnc.com/product/pcm-...rsion-harness/


** To be clear, these two products mentioned and the two before that do not use ISS not because we are too lazy to hook up but there are some odd application bugs that removing it fixed.. Like one was with cruise control

[trucknut44]

So, cutting to the chase, what are my options? I am also sending the current files to the original tuner, he says they have used this combination successfully in the past. Is there any OS I can switch to? Will he have to get a newer transmission?

[Alvin]

Have you tried maxing the misfire tables? Just in case?

[daniel6718]

Sorry to hijack, does the e67 need an iss to lockup, I can command lockup but not get it through settings. I have don?t an 80e swap with the relay mods not a set swap.
I turned the iss off in the file an disabled errors

[Alvin]

No they do not need ISS to have TCC lockup. They do need to be free from misfires (detection) and have a good brake signal. Most applications it is 12v when brake NOT applied.