P084B Transmission Fault, Slipping

[FordConvert]

'21 Lariat PB Max Tow

Back in May I started getting this warning during sustained freeway-speed hill climbs:

The powertrain fault is P084B when this happens - "Transmission fluid pressure sensor/switch "H" circuit range..."

The vehicle seemed unaffected, but I took it in for service anyway. Four appointments since May. Twice they've replaced a sensor, but the fault keeps occurring.

It's recently been getting worse. Used to be just sustained hill climbs at freeway speeds, but now it almost every time I'm on the freeway. I get a notification in my FordPass app every time - I have many dozens of these messages and haven't deleted them.

Over the past few weeks this is now happening on sustained hill climbs:

Notice the transmission is not shifting. I'm not pulling or hauling anything. It feels like it's slipping/briefly losing power when the RPM's surge. This occurs in modes Normal, Eco, and Slippery, but never yet in Tow/Haul when I'm actually pulling a trailer.

I have a fifth service appointment with an "advanced" tech next Tuesday (every time I call in to say it's not fixed, the next appointment is at least a month out). Fingers crossed it's not a part that's out of stock forever!

Any thoughts from the ever-wise forum collective??

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[FordConvert]

Update for those who come across this same issue. Tech convinced Ford to replace the transmission auxiliary fluid pump and associated parts. Will update when work is complete. Pump is back ordered for now.

 

[notabot]

Sucks to be having these issues. What's the build date on your Lariat PB?

 

[FordConvert]

Sucks to be having these issues. What's the build date on your Lariat PB?

June 28, 2021

 

[notabot]

thanks!

 

[22Platinum]

I'd be sad without a trans replacement as it doesn't take long to burn up the bands slipping like that. Sucks.

Wildly it might have been better to lean on it when its slipping and burn it up completely, forcing the R&R

 

[Snakebitten]

I'd be sad without a trans replacement as it doesn't take long to burn up the bands slipping like that. Sucks.

Wildly it might have been better to lean on it when its slipping and burn it up completely, forcing the R&R

Not that kind of transmission.

I'm not saying that there aren't components that could experience accelerated wear, but the 10r80 is a long ways from the Era of slush-box automatic transmissions.

 

[22Platinum]

Hard to say what is slipping from here to be sure

But if it's any of these:

It won't take long to need new ones.

 

[Porpoise Hork]

Update for those who come across this same issue. Tech convinced Ford to replace the transmission auxiliary fluid pump and associated parts. Will update when work is complete. Pump is back ordered for now.

Seems like a percentage of 21+ 10R80's are having issues with the aux pump. Makes me curious how many are faulty.

 

[FordConvert]

From what I understand, the aux pump keeps pressure up when ICE is off. Not sure how a faulty aux pump causes "slipping" when climbing hills at freeway speeds.

 

[Porpoise Hork]

Not sure how it would either. One thing you can try if you haven't taken it back in yet. Clear the adaptive tables with Forscan. One of the parameters the adaptive tables do is set pressures and detect for slipping under different conditions. If the system has picked up an off pressure setting that is allowing the clutches to slip, clearing the tables may help fix it. This is something the tech should do after servicing the transmission anyway. So it's worth a shot.

Reset it and drive it calmly on surface streets for about 30 minutes to set the initial values. Then over the next 250-500 miles it will "re-learn" your driving style and adapt to it.

 

[notabot]

I'd be sad without a trans replacement as it doesn't take long to burn up the bands slipping like that. Sucks.

Wildly it might have been better to lean on it when its slipping and burn it up completely, forcing the R&R

Agree! Break it properly so F has to fix it...

 

[FordConvert]

Update. Slipping only seems to happen in gears 8-10. When I lock those out and keep it at 7 there is no slipping.

Is it an RPM thing, or something with that set of gears?

I did notice the slipping once in gear 6, however.

And sometimes when I pass through 5th it slips.

36k miles on the truck. *sigh*

 

[FordConvert]

Update.

Pulled a trailer to the dump today and I think that did the trick. Serious slipping. Sometimes hitting redline during shifts under load. Got the trailer back to the site okay but it got worse on the way home. Eventually got the message to pull over and stop. Was able to restart it and limp it to a nearby dealership. They will look at it tomorrow. 38k miles. Max tow package. Trailer was 7500 loaded.

 

[FordConvert]

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