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Discussion Starter · #1 ·
During a few thousands km I driving my 2019 ct6 sport. There is a very interesting “feature” I found.

At first, I feel very upset about this 10 speeds transmission. It clog and jerky at low speed (maybe under 40 km/hr) while I release the gas pedal totally. The car can’t “slide” smoothly like the other car I have owned ( ex. Chrysler 300M or TC). I chage to manual mode to see the gear changing condition. As the gear position change form high to low ( 7th à 6th à5th à 4th …..) the clog condition is getting worse. It feel really uncomfortable. But while the gear position down to 3rd or 2nd… the clog condition is GONE. That’s very serious problem. I think I buy a low milage car with bad condition transmission. Extreme upset and disappoint come to me…. What kind of Cadillac it is…..

Last week, I drive my car with very bad mood because of heavy traffic and clog transmission. I changed the left side of cluster screen to “Fuel Economy”. There are 3 info (average , best and Instant) on it. There is why the transmission clog and jerky I found….. While the car speed reach to 30 or 40 km/hr or higher and release the gas pedal totally. the car keep “SILDE” with no brake apply. The Instant gas consumption will drop to “zero” after 1 or 2 second. Yes.. It shows “0.0” on cluster. It seems no gas supply to engine. Engine is shutdown but still “driven” by transmission ( or wheel). The gear position change to lower automatically while the car speed getting lower. When car speed lower than 25 or 30, the gear down to 3rd. The feeling of clog and jerky is most obviously. If lower approx. 20km/hr, the “Instant gas consumption” start to going up, that means the engine start to running by itself, not “driven” by wheel. Then the feeling of clog and jerky is all “GONE”. When car is total stop. The instant shows “-.-“, not “0.0”.

It seems “0.0” instant gas consumption is on purpose while the gas pedal release totally. No gas supply to engine for better MPG. Of course the engine driven by transmission while engine has no power ( no gas supply). That’s why I feel clog and jerky. I was blamed cadillac unjustly. No transmission problem at all.

IMHO, better MPG is great, but for Cadillac, especially for high end Cadillac sedan. The importance of comfortable driven experience should not lower than better MPG.

I am not sure this feature is part of “active fuel management”. I don’t think so. It’s total different idea for the same purpose. I can’t find any technical info about this “feature”.

maybe …. It just abnormal of my ct6…… Have your ct6 the same “feature”?
 

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'19 CT6 Platinum 3.0TT
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I haven't had the transmission problem you're describing, but yes, the fuel shuts off above a certain speed while you are coasting (foot off the gas). Every GM car I've had since my 2003 Corvette has done this. Your transmission shouldn't be doing that.
 

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Discussion Starter · #3 · (Edited)
I haven't had the transmission problem you're describing, but yes, the fuel shuts off above a certain speed while you are coasting (foot off the gas). Every GM car I've had since my 2003 Corvette has done this. Your transmission shouldn't be doing that.
Thanks for your info. it seems that this feature is too "normal" to emphasize it. Ha..... This is my first GM...

At high speed, I can't feel any problem of transmission, but while car on low speed and fuel shuts off. It feel clog transmission.. . just like ENGINE BRAKE. If fuel re-supply to engine... car "coasting" smoothly again..... is that normal?

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2018 CT6E, old: 2014 XTS Vsport, 2005 CTS-V, 2004 CTS-V.
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DFCO - declaration fuel cut off. The engine does just free wheels when off the throttle. GM has doing this for decades now.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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My 2002 STS shuts off the fuel injectors during extended coastdowns BUT the downshifts are smooth and not jerky in any way. That may be the 4-speed 4T80E transmission and coastdown jerkiness may be an artifact of the 10 speed?

Injector cutoff is signaled by a "blurp!!" in the exhaust note and instantaneous gas mileage goes to 70 mpg.
 
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