# 2018 1.4l automatic no 6th gear



## BlackedoutRedline18 (Dec 12, 2020)

hello, I have a 2018 Cruze 1.4L with an automatic trans the other day I was getting on the highway and I noticed I was stuck in 5th gear. after I got over 80 it shifted into 6th but when I went back down to 78 mph it bucked back into 5th gear. later that day I took it out again and it didn't do it. My local Chevy dealer said that couldn't do anything for me because that speed is over the listed speed limit in the area and he would be putting his mechanic at risk. Wondering if anyone has this issue and what it might be. Car only has 54k on it and I only have an intake and a cat back exhaust. so its not like its tuned and built. any help would be great also have a video of it happening below.

Kurt


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## JLL (Sep 12, 2017)

That's the transmission telling you your driving to fast while using you phone and it's dangerous.  

Welcome to the forum.

BUMP for help for the OP.


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## 17Hatch6MT (Dec 28, 2015)

Fluid condition and level? Temp gauge registering normally?


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## Taxman (Aug 10, 2017)

Seems like mine shifts into 6th when cold, but won't lock the converter until the transmission warms up.


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## LukeLeeOFC (Feb 12, 2021)

BlackedoutRedline18 said:


> hello, I have a 2018 Cruze 1.4L with an automatic trans the other day I was getting on the highway and I noticed I was stuck in 5th gear. after I got over 80 it shifted into 6th but when I went back down to 78 mph it bucked back into 5th gear. later that day I took it out again and it didn't do it. My local Chevy dealer said that couldn't do anything for me because that speed is over the listed speed limit in the area and he would be putting his mechanic at risk. Wondering if anyone has this issue and what it might be. Car only has 54k on it and I only have an intake and a cat back exhaust. so its not like its tuned and built. any help would be great also have a video of it happening below.
> 
> Kurt


I'm having this same issue. Did you ever find a fix for it? What was the issue?


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## Barry Allen (Apr 18, 2018)

This is discussed in other threads. If it's cold ambient temperatures with high humidity levels, the transmission will remain in 5th gear to prevent moisture from freezing in the charge air cooler and intake parts. The air temperature through the charge air cooler has to remain high enough to not freeze so running it in 5th keeps the boost level up. When you reach a high enough speed that 6th gear can be used with a high enough boost level to keep everything from freezing, it will do that just fine.


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## loraleewilliams2 (11 mo ago)

LukeLeeOFC said:


> I'm having this same issue. Did you ever find a fix for it? What was the issue?


 I’m wondering this myself. Mine doesn’t matter if it’s cold outside or not.


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## loraleewilliams2 (11 mo ago)

Barry Allen said:


> This is discussed in other threads. If it's cold ambient temperatures with high humidity levels, the transmission will remain in 5th gear to prevent moisture from freezing in the charge air cooler and intake parts. The air temperature through the charge air cooler has to remain high enough to not freeze so running it in 5th keeps the boost level up. When you reach a high enough speed that 6th gear can be used with a high enough boost level to keep everything from freezing, it will do that just fine.


 Mine is doing the same thing. Has been doing it intermittently since October at 70 degrees. 24 degrees out and it doesn’t start for 20 miles at 75. So I think mine is not necessarily from the cold?


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## Barry Allen (Apr 18, 2018)

loraleewilliams2 said:


> Mine is doing the same thing. Has been doing it intermittently since October at 70 degrees. 24 degrees out and it doesn’t start for 20 miles at 75. So I think mine is not necessarily from the cold?


70 degrees is out of the question. I can't answer to that.

24 degrees can happen. It has to be a combination of air that has high enough humidity to be significant moisture content and then temperatures that can freeze that moisture inside the intercooler at highway speeds. I don't know how the ECU determines humidity, but presumably there is some sort of sensor for the air flowing through the intake. If you are cruising along at highway speeds and you hit a pocket of air with high humidity (conditions can change from mile to mile as you drive, depending on ambient conditions) it's easily possible for the ECU to kick down to 5th gear if you are encountering icing conditions.


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## loraleewilliams2 (11 mo ago)

Barry Allen said:


> 70 degrees is out of the question. I can't answer to that.
> 
> 24 degrees can happen. It has to be a combination of air that has high enough humidity to be significant moisture content and then temperatures that can freeze that moisture inside the intercooler at highway speeds. I don't know how the ECU determines humidity, but presumably there is some sort of sensor for the air flowing through the intake. If you are cruising along at highway speeds and you hit a pocket of air with high humidity (conditions can change from mile to mile as you drive, depending on ambient conditions) it's easily possible for the ECU to kick down to 5th gear if you are encountering icing conditions.


I have had it run 6th gear last few weeks when it was -20. Been fine for 3yrs. This just started at 90,000 miles.


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## Barry Allen (Apr 18, 2018)

loraleewilliams2 said:


> I have had it run 6th gear last few weeks when it was -20.


At -20 (either F or C) there is so little humidity in the air because it's already all frozen out. Whatever sensors interfacing with the ECU don't have a problem with that because the intercooler won't freeze up in those conditions.

It has to be specific conditions where there is high humidity and a temperature low enough to possibly freeze up inside the intercooler.


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