A750F Transmission P2714 - Pump Starved for ATF Even After Topping Off?

I bought the truck with 130K on the clock and soon afterward did a complete flush of most fluids, including the transmission. When draining the transmission (A750F), I recall there being an unexpected extra ~1.5 quarts of fluid present. After the flush was complete, I topped off the fluid, started the engine, waited for the AT oil temp sensors to be in the 95 - 114 degF range (using TechStream), opened the overflow plug, and let the extra fluid run out until it slowed to a trickle.

Now, 5K miles later, I got a P2714 code. The CEL and code appeared after what felt like the truck had entered limp mode, with very limited acceleration. This happened in a hilly location. And, come to think of it, I'd seen the same reduced power sporadically in the past when driving at low speeds in rough, hilly terrain. In these previous situations, the truck had quickly returned to normal operation on its own. In this most recent situation, (the only one that triggered a CEL), clearing the code returned the truck to normal operation, and I drove 300 miles home without issue.

Upon returning home from this trip that triggered the CEL, I checked the fluid level. A little bit trickled out, perhaps what was just caught at the top of the stand-pipe in the pan, so I added a half quart of WS ATF and used the same procedure described above to finalize the level. ATF definitely came out of the check plug when I opened it.

I've since installed a line pressure gauge to monitor the pressure inside the transmission. The drive and reverse idle pressures appear normal: 55 and 75 PSI, respectively. The D position stall pressure test was slightly low (195 PSI) but the R stall pressure test was in spec (195 PSI). Most interestingly, after the D stall pressure test, I noticed the line pressure drop precipitously to 15 PSI range before bouncing back to a normal idle pressure. Also note that the engine stall speed was within spec at 2450 RPM.

I also ran a test of the SLT solenoid using TechStream to turn the solenoid on and off. When the SLT is commanded off, the measured pressure was 155 PSI. I'd love to know whether this is in spec because I don't see an acceptable range anywhere in the Toyota documentation.

I also performed the shift lag time test described in the Toyota manual and the average times (1.07s for D and 1.26s for R) were well within spec.

In the process of all this testing, I noticed something that I find intriguing: when the truck is allowed to creep in reverse, at slow speed, when stopped on a 5 degree incline (entrance to my driveway), the line pressure drops to 20 PSI.

This has left me wondering whether the pump was being starved for oil. So, I added another quart, and the active pressure test (with the SLT solenoid commanded off) rose to 195 PSI. I also noticed that the D idle pressure rose from 52 PSI to 55 PSI and where there was +/-2PSI of fluctuation previously, the needle is now more steady. Additionally, now when stopped, after creeping backward, on a 5 degree slope, the pressure only drops to 40 PSI. The pressure drop also happens when driving forward and stopping on a 5 degree slope, but it is less pronounced.

So, my confusion: is the pump being starved for oil? And why, even after adding an extra quart of ATF? Could it be ingesting air from some other condition?

Am I topping off the level incorrectly?

Am I losing ATF somewhere? I don't see any drips underneath the truck. Could ATF accumulate in the bell housing or between the transmission and the transfer case and not leak out for months? Could ATF be leaking into the coolant system via the ATF heater without me noticing it? (Previous engine oil cooler failures on other vehicles have been impossible to miss. And, coolant level on the truck is unchanging.)

Should I add another 0.5 - 1 quart of ATF to see if the situation improves further?

Here is a video of the pressure drop phenomenon: https://youtu.be/tZMludil4Kk Check the description for details of what's happening.

Edit: for anyone else looking to pressure test their A750E/F, you'll need a UN 5/16"-24 to NPTF 1/8" adapter. I purchased mine from McMaster-Carr, part number 51205K546.

 

I don't have any answers for you but I'm following along. You don't see many issues with 750 series transmissions.

Hopefully you get it figured out soon.

 

After reading your post and watching your video , I am pointing to a cross leaking valve body .
When a valve body cross leaks , rather than supply the circuit with pressure and fluid , the fluid bleeds off to another circuit or back into the transmission pan .
You purchased the truck with 130k
Do you know how the truck was driven before you purchased the truck ?
Was anything done to the transmission at the dealership ?
Did you remove the transmission pan when you performed the transmission flush ?

 

Thanks for responding, @gearcruncher!

The truck spent its life in the greater Bay Area and made regular trips to the dealer up to 105K miles with a variety of fixes being performed including a replaced cam seal, replaced steering rack, replaced CV boot, transfer case seal, timing belt at 83K, etc. It seems that the owner at the time was generally proactive about taking care of the vehicle . In the Lexus service history, there was nothing obviously transmission related, but the owner complained first at 92K of "WHINE HUMMING TYPE NOISE FROM ENGINE OR TRANSMISSION" and then at 102K of "NOISE FROM THE ENGINE AREA WHEN STOPPING". In both cases, the dealer could not replicate the problem and no service was performed.

I have a few 3rd party service records between 105K and 130K (e.g. SAI blower), but nothing transmission related. The seller (a college kid) and his father (who had loaned him the money to buy the vehicle) seemed like decent people who weren't trying to hide anything. I was left with the impression he was selling because gas was unaffordable at the time (right around peak at $7/gallon).

I did remove the pan when I did the flush, and I replaced the strainer/filter at the time. The fluid was fairly dark. Unfortunately, I didn't take pictures, but I don't remember it smelling burned, or it causing me to be overly concerned given there was no indication that it has been changed previously. The pan magnets had some very fine particulate film on them, but again, nothing that raised obvious red flags to me at the time.

Also, in the process of topping off the fluid this past week, the fluid coming out of the transmission is bright red and looks good. Granted, it only has 5K miles on it, but I'm hopeful that I haven't destroyed any clutches yet.

While I've never done it before, I am setup to perform vacuum testing of the valve body (including the Sonnax vacuum plate). My biggest concern is whether I need to be prepared to replace any internal rubber seals after dropping the valve body. I'd rather have parts on hand than be caught out waiting for esoteric parts to arrive in the small town where I live. Do you have a list of things I could preemptively order from the local Toyota dealer so that I'm prepared?

Where do you suggest I start? Are there additional tests I could do before dropping the pan and pulling the valve body to try and help isolate any potential cross-leakage? I'm happy to record additional video, and I am setup to simultaneously record the pressure gauge, the instrument cluster, and TechStream, if that helps.

 

A quick question . Was the transmission cold or warm when you were checking your line pressure in the video ?

It takes me a while to reply sometimes ... I am always at work

You have done a lot of homework so far . Before we jump into Sonnax products , read this if you havnt seen it yet . You have similar symptoms
http://bluegrasstoday.com/wp-content/uploads/2012/07/a750e_shudder.pdf

 

The transmission was probably on the cooler side when I took that video (100 degF, if I had to guess). I can re-test with the transmission warmer, but given the cold weather, and it's injured condition, I'm hesitant to really hammer it.

I had read the ATRA article you linked, and I already have a new SLT solenoid on the way from Oregon Performance Transmission that should arrive in a day or two. I'd been waiting until that arrived to drop the pan. Once it does, I'll check the operation and resistance of the old solenoid before installing the new. I'm assuming I can install the new SLT solenoid without removing the valve body?

Do you know of links to videos showing normal A750 line pressure during operation? Without something to compare to, it's difficult for me to evaluate what may be wrong.

Thanks for the continued feedback, @gearcruncher. I'm happy just to have someone else thinking about the problem.

 

The new SLT solenoid arrived, so I opened up the transmission. Never have I been so happy to see a destroyed o-ring. I feel like this confirms one of my initial suspicions that the pump was likely ingesting air. I'll replace the SLT solenoid so long as I have it, and I'm feeling optimistic that I'll be able to call this case-closed. Will report back once I can get the new o-ring from the dealer and have things buttoned-up.

 

That would definitely cause it to suck air especially on an incline.

 

Thats great!!!! I wish my issue is as easy as yours.