Torque converter lock-up with OD off

I have the A750F automatic 5-speed transmission. When towing last weekend with the OD off, the torque converter did not lock-up once in 4th gear over a 50 mile stretch of highway. Same on the way back home. Two questions:

1. Is the torque converted supposed to lock-up in 4th gear with OD off?
2. Is overdrive really just the 5th gear? When in 5th gear and turning OD off, truck shifts back into 4th. No impact of using the OD button in any other gears.

I'm using an UltraGauge to monitor both the trans temps and torque converter lock-up status. A few observations:

- I was towing a 4500lbs trailer (loaded weight)
- I was cruising 65mph to 70mph at mostly flat highway
- 265/65/17 tire size running about 3000rpms with OD off in 4th gear which has a 1:1 ratio
- Trans pan and torque converter temps were at 167 degrees for the entire stretch
- Did a transmission drain and fill a few weeks ago with Toyota WS fluids

When I turned OD back on, the truck shifted into 5th gear and torque converted locked-up. However, the TC trans temps started rising to 190 degrees while the trans pan temps stayed at 167. As soon as I turned OD off, truck shifted back into 4th gear, trans temps returned to 167 degrees, and torque converted did not lock up.

I read that the A750F has an intermediary flex TC lock-up status that is in addition to the full lock-up.

Truck ran just fine as is, but curious what effect OD and TC status have on each other. Any insights?

 

OD is typically after the highest gear or is the highest gear. In your case it would go to 5th then OD like going to 6th or maybe 5th is OD. So when in 4th, and OD is off, you are in 4th.

Sounds like your TC was locked based on the temperatures you are reporting. Also TC lock/unlock in Ultragauge is not accurate. My co-worker had a Ultagauge and told me lock/unlock reading is not accurate and flips on/off for no reason.
I was curious because I wanted to get the equation for my scan gauge and he told me it's useless.

Based on your temperature readings, when OD was on, your TC was most likely unlocked and/or switching back & forth between locked/unlocked and your temp was higher. WHen OD was off, you were in 4th & locked and your temp was lower. It's working as it should. In 4th, torque converter stays locked more often than 5th/OD. that's why they recommend towing in 4th as opposed to higher gears.
Just ignore the ultragauge lock/unlock indication.

 

btw, best indication that TC is locked, is when pan and TC temperatures read the same. If you start seeing TC temp going higher than pan, then TC is unlocked.
This matches what you had observed ... That's why I said ignore the ultragauge lock/unlock indication.

 

That makes sense. The UltraGauge lock status doesn't seem reliable and shows too many discrepancies.

 

My 06 would lockup in 4th. My truck was loud and you could hear it lockup. 4th is quicker to lockup than 5th. Put truck in 4th at speed and touch brake pedal, converter should unlock then watch tach should lockup, you will see a slight drop in engine rpm.

 

After a crash course in OBD communications, I was able to get my UltraGauge to show the correct lock-up status. After changing the programming, UltraGauge now shows the torque converter lock up in 4th and 5th gear. It also locks up in 4th gear with OD off. The lockup coincides with a slight drop in rpms.

 

What code do you use to get torque converter lock info?

Actually I have a Scangauge not an UltraGauge, not sure if they use the same codes or not.

 

Can you post what changes you made to your ultragauge or what is your current equation?

I can send it to my friend to try and if it works in his truck (6 spd auto) I can tweak it if needed and try it in my scangauge. I've seen other equations and there is lots of similarities between ultragauge and scangauge equations. it may or will require minor tweaks.

 

Yes, OD is just 5th gear. The term overdrive simply indicates that the ratio of that gear is higher than 1:1.

 

On the UltraGauge, I changed the RPos value to 1B01. Original value was 1F01.

I validated the settings in Torque Pro too. The equation there is bit(A:4).

I use the command 21DA (Torque) or 07E021DA (UltraGauge)
The response comes in as 61DA1506 (Torque) or 0461DA1506 (UltraGauge) when locked.

The response HEX value 15 contains both the gear you're in and lock up converter status.

HEX 15 converts to 00010101 binary.
The 5th position (counting from the right) contains the lock-up status.

Haven't used ScanGauge, but you should be able to get to this specific bit as well.

 

Nice job!
is the 5 in 15 the gear you are in?

btw, my friend was working on tire pressure equation for his ug. He told me you can read it. Not sure if he has come up with it or not. You are much faster maybe you can figure it out.

 

Yes:

01 - 1st gear, unlocked
02 - 2nd gear, unlocked
03 - 3rd gear, unlocked
04 - 4th gear, unlocked
14 - 4th gear, locked
05 - 5th gear, unlocked
15 - 5th gear, locked

My TPMS sensors are shot, so not sure how much help I can be on those values.