4th gear and TCC lockup issues

**99coupegtp** · 11-16-2018

Hey all,

I have a 4T65E-HD with around 25k miles on it and a couple days after a recent road trip with some vigorous mountain carving it has started to do strange things.

At speeds less than 50mph 4th gear and lockup will work most of the time but TCC lockup will disengage and the transmission will downshift to 4th under light throttle conditions despite the PCM commanding 4th and lockup.

At interstate speeds, 60mph+, the issues with 4th and TCC lockup are even worse.

These issues seem to get a bit less noticeable after the transmission fluid has reached 160-170*F but it still doesn't work perfectly.

Anyone have any ideas what the cause of this may be?

Sent from my LGUS997 using Tapatalk

**99coupegtp** · 11-16-2018

Originally Posted by 99coupegtp

At speeds less than 50mph 4th gear and lockup will work most of the time but TCC lockup will disengage and the transmission will downshift to 3rd under light throttle conditions despite the PCM commanding 4th and lockup.

Oops, meant to say that it will downshift to 3rd, not 4th.

**selliott** · 11-17-2018

Mine does this and not sure why, I did figure that when mine does it, it will have a pending code. Not sure what the code is bc I never have my scanner. It doesn't trip the cel and won't show up in the aeroforce but as soon as I hit clear codes it goes into lockup and shifts normal. If I'm driving in town I always leave it in 3rd bc if I have it in drive it's always down shifting. Not sure if you're having the same issue but you might check pending codes.

**Scottydoggs** · 11-17-2018

overdrive aka 4 th dont really lock up till the tranny is warmed up.

**99coupegtp** · 11-18-2018

Yeah I've read that but this is way different than that. Its commanding lockup according to the TCC duty on the aeroforce gauge.

The way it's working now is not the way it's worked for the past 2+ years.

**99coupegtp** · 11-18-2018

Originally Posted by selliott

Mine does this and not sure why, I did figure that when mine does it, it will have a pending code. Not sure what the code is bc I never have my scanner. It doesn't trip the cel and won't show up in the aeroforce but as soon as I hit clear codes it goes into lockup and shifts normal. If I'm driving in town I always leave it in 3rd bc if I have it in drive it's always down shifting. Not sure if you're having the same issue but you might check pending codes.

Ah, I was hoping the aeroforce gauge would get trans codes... Well since I now know it doesn't, I'll take it somewhere and have it scanned. Thanks!

**selliott** · 11-18-2018

Originally Posted by 99coupegtp

Ah, I was hoping the aeroforce gauge would get trans codes... Well since I now know it doesn't, I'll take it somewhere and have it scanned. Thanks!

I'm not sure if the aeroforce reads trans codes or not I just know that pending codes don't show up. If your out driving and it does it again try clearing codes and see if it immediately goes into lockup.

**99coupegtp** · 11-19-2018

Originally Posted by selliott

I'm not sure if the aeroforce reads trans codes or not I just know that pending codes don't show up. If your out driving and it does it again try clearing codes and see if it immediately goes into lockup.

Gotcha, either way I had O'Reilly's scan it yesterday and there were no trans codes.

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