My experience with my 4L80E on T42 swap with

[Mean Green Z28]

Hope this helps someone in the future ... after a fresh rebuild on the trans and converter, I wanted to make sure everything was GOOD before we did any damage ... I'll go through all the steps we followed and discoveries etc. I'm not an expert at any of this but I've learned a lot. If you wanna get down to the troubleshooting, just go down to the ******

Truck is a 2009 Silverado LY5 ... E38 ECM and T42 TCM, running a 4L80E swap on 4L60E tune with an early Frost conversion harness with the external PRNDL switch harness pinned into it as the 2009 4L60E didn't have it on the side of the trans and did it internal. It also had an internal ISS that I haven't wired in on the 4L80E as that's not really required.

Right after putting my 3200 Stall in, the transmission started overheating and eventually started making metallic noises and so we pulled the trans and sent it out to be rebuilt and the converter was also sent out to be freshened up. Turns out some of the trans connector pins were bent and also wan't making full contact as the plug had been pushed into the trans. I'm hitting my head on the wall for not noticing this during install. The clutches were all burned out and the converter lockup clutch was bare metal ... it wasn't pretty. After a flush of the cooling lines, everything was re-installed and fresh fluid filled.

Drove her around and although things seemed to work fine but we noticed the temps started climbing again. Came back to the ship and put Original tune in with only a few numbers like gear ratios etc. changed and ISS codes turned off. Everything seemed to work fine and temps stayed normal ... so something I did when copying all the 4L80E tables from a Van may have affected it? keep reading.

Drove her home and had a check engine light turn on and the TCC never locked up ... also temps started rising a little bit (210F) before I got home. This was pissing me off...

Next morning ... pretty cold out ... drove the truck and noticed no TCC lockup on a trip to Dentist. But after, it seemed to lock up on my way to the transmission shop; he was gonna ride with me with his scanner when the weather was better than yesterday's rain. He read the 2 codes as "low idle" and "brake pedal switch issue" < not exactly what it said but you get the point.

****** TROUBLESHOOTING AND DISCOVERIES ******

He noticed that as soon as I took off, the TCC PWM value would go directly to 99% and stay there; but the TCC On/Off signal was still OFF. Now this 99% value wasn't surprising as we had the Min PWM tables maxed as we wanted to eliminate PWM. BUT, the converter never locked up or made any effort. It would have been messy if it did too, as it maxed out immediately as it detected any movement. When the Lockup signal turned on, the TCC locked up as expected. He was worried about the TCC PWM signal status not doing anything and advised we try to figure out what the heck the TCM was doing.

Speaking to another tuner in the area who's done these swaps, he stated that the PWM signal is probably internal not being sent to trans until certain parameters are set? Well the trans shop wasn't buying that as he said that's the output and not an internal value.

****** FROST HARNESS ******

Brought the truck home and took out the Frost Harness to check if the relays were bad or anything of that sort. The relay that swapped Solenoid B status was fine and left alone.
Tracing TCC/PWM wires between the ends and the relays, I noticed that the PWM signal goes through the N/O terminal of the relay on its way to the transmission (when not active, a 10K ohm resister is branched off to avoid the MIL). This shows why the PWM signal never did anything until the on/off signal was set. But, this would have also saved us as we maxed out the Min PWM table ... having the PWM signal maxing out off of idle would have created a mess of things.

In my situation, since I didn't need PWM anymore, I ran the TCC On/Off wire directly to the PWM input signal of the trans (just as everyone else does). Left the PWM signal connected to resister to avoid any MIL issues.

Here's a bad drawing with my understanding of the controls and how I think it should've been. Although thinking my way is will make it act like there's no PWM when coming to a stop as I've noticed it stays locked till the MPH is pretty low (helps braking though!) I'd have thought the Relay activation would have sent ground to the PWM and run the TCM PWM signal when not as shown. I'm open to your thoughts.



****** BRAKE PEDAL SWITCH ******

Also read that the brake pedal switch MIL we saw may cause TCC and Cruise control issues. Was gonna buy a new one, but decided to take the existing one off and clean the connections in case they were dirty.

A combination of these worked as I now have very positive TCC lockup that I can tune and have no doubt that PWM can cause any issues with burning up my clutches etc. if not tuned right.

****** LESSONS LEARNED ******

Having the Harness as it was requires running full PWM control, you cannot max out the Min PWM table as it will mess up drive ability in this application.
Be careful when connecting the Trans harness connector.
The brake switch can affect a whole bunch of shit!