Another question about torque converter lock up. 3rd gear.

So… I have towed quite a bit recently with my 2020 OR AT and use OBD fusion to watch trans temps and lock up status of the the TC.

I see lock up in 4th, 5th and 6th and understood that no lock up happens in 3rd.

I just emailed OTT tuning and asked if they are able to make 3rd gear lock up and their response was very short and left me with questions...
“It’s has 1/2 lock from the factory and that is kept.



Yes we adjust shift points.



J”

What is 1/2 lock?

Whilst researching this I came across a 2nd gen thread that talked about their 3rd gear locking up in S mode but not D mode.

In 8k miles of towing I never saw 3rd gear lock up.

Does anyone have info on 3rd gear 1/2 lock up?

Photo of my OBD dashboard showing top left red circle that changes to green upon lockup.

Thanks

 

So I asked the tuner and got a response…
“3rg gen added a slip lock or ½ lock in 3rd to prevent torque converter shudder found in the 2nd gens.

It not a full lock, just 50%”

 

Not exactly sure how Toyota's system works but this is my general understanding of how the TCC control works on most vehicles.

The torque converter clutch is controlled by modulating pressure to it so TCC slip can be regulated to whatever the PCM's desired slip ratio is, the torque converter is usually not locked in lower gears and under hard acceleration to allow the torque converter to operate as a torque multiplier. In higher gears and light loads the TCC is locked to increase fuel economy and decrease heat generation.

Most vehicles never fully lock the torque converter even in so called lockup they typically allow around a 20-70 RPM slip (No one I've asked seems to know why exactly this is but IMO it's why so many modern vehicles suffer from TCC shudder).

I'm pretty sure 3rd gens have a Tow/Haul mode, if your towing pretty heavy it would be a good idea to use it.
Again not 100% sure on Toyota but generally when it's enabled it:

Raises transmission line pressure to give firmer shifts and help prevent clutches from slipping under higher loads.
Raises transmission shift points to help keep the engine in the powerband and reduce gear hunting.
Keeps the torque converter locked up more to reduce heat generation.
Provides engine braking by downshifting the transmission on deceleration (some trucks also use brake input to determine how aggressively to downshift).

 

Sub'ed for future responses.