# doors lock and drive gear downshifts suddenly!



## Black Tammy (Jul 8, 2019)

JUST bought a 2012 Chevy Cruze LTZ, a one-owner car and looks beautiful. After driving it for 20 minutes on the expressway, suddenly the doors locked and simultaneously it downshifted to low gear when I was driving approx 60-70 mph, which almost gave me a coronary. Now almost a week later, I've experienced the same thing going at a high speed, and at a low speed. What the heck? Should I get a diagnosis of electrical system? And transmission check? has anyone had these specific symptoms?


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## ChevyGuy (Dec 13, 2014)

Is anything plugged into the OBD2 port? Is there any other malfunction in the car? Any aftermarket stuff? The symptoms suggest something messing up the computer bus. 

We've had reports of odd electrical gremlins before, but I don't remember reading anything like this.


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## Black Tammy (Jul 8, 2019)

Nothing plugged in, no other malfunctions that I've seen yet (owned the car less than a week), no aftermarket stuff. I'm really losing sleep over this. Not possible to feel safe driving when there's a possibility of downshifting suddenly while driving at expressway speed. Yikes!


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## Black Tammy (Jul 8, 2019)

Could the computer also affect the gear downshift problem too? or do you think I have both computer and transmission problem?


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## ChevyGuy (Dec 13, 2014)

The Cruze is heavily computerized. Even simple things like power windows and turn signals are run by computers. Computer module failure is rare, but anything screwing up the buss could cause a ton of problems. For example, a failing side detection system can messing things up. You might want to check and see if your car was equipped with side-detection or park assist. The prior owner may have deactivated it because it failed, but never disconnected it or secured the wiring. Which brings up a question - did this happen when the street were wet? Water getting into things could cause problems.


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## ChevyGuy (Dec 13, 2014)

The other thing you might do is pull the battery and the battery tray. I seem to remember there's a module under there and a leaking battery can ruin it.


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## Black Tammy (Jul 8, 2019)

ChevyGuy said:


> The Cruze is heavily computerized. Even simple things like power windows and turn signals are run by computers. Computer module failure is rare, but anything screwing up the buss could cause a ton of problems. For example, a failing side detection system can messing things up. You might want to check and see if your car was equipped with side-detection or park assist. The prior owner may have deactivated it because it failed, but never disconnected it or secured the wiring. Which brings up a question - did this happen when the street were wet? Water getting into things could cause problems.


There was no water at all on the streets when this has happened. But the used car dealer from whom I bought the car is going to get a whole new computer for the car. He will send it to Chicago where they'll rebuild it with a lifetime guarantee. Does this sound okay to you?


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## ChevyGuy (Dec 13, 2014)

As they say, "proof is in the pudding". A Chevy dealer might replace and reprogram a module. This is the first I've heard of sending one out for repair. Whatever works...

I wonder what they're sending out? The BCM controls the door locks. I think the ECM commands the transmission module.

Uh, wait a sec. Doesn't your car lock the doors when you shift it into gear? Mine does, but I don't remember of that's a "personalization" option (controlled though the radio). It makes me wonder if you've got a bad or misaligned gearshift switch.


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## Blasirl (Mar 31, 2015)

Welcome Aboard 

moved from introductions


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## RichLo1 (May 31, 2018)

+1 to the last comment about gear-shift switch. The door locks are a safety device and cannot be deactivated. Once you move the lever out of park all the doors should lock.


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## Black Tammy (Jul 8, 2019)

ChevyGuy said:


> As they say, "proof is in the pudding". A Chevy dealer might replace and reprogram a module. This is the first I've heard of sending one out for repair. Whatever works...
> 
> I wonder what they're sending out? The BCM controls the door locks. I think the ECM commands the transmission module.
> 
> Uh, wait a sec. Doesn't your car lock the doors when you shift it into gear? Mine does, but I don't remember of that's a "personalization" option (controlled though the radio). It makes me wonder if you've got a bad or misaligned gearshift switch.


This is really helpful, thank you so much! If they send the "computer" to Chicago for repair, I'll be without a car for 10 days. The cheapest rental will be $360. More Yikes!


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## Black Tammy (Jul 8, 2019)

Black Tammy said:


> This is really helpful, thank you so much! If they send the "computer" to Chicago for repair, I'll be without a car for 10 days. The cheapest rental will be $360. More Yikes!


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## ChevyGuy (Dec 13, 2014)

RichLo1 said:


> The door locks are a safety device and cannot be deactivated. Once you move the lever out of park all the doors should lock.


I confirmed this last night. The only thing I can personalize is the unlocking. Now, that's not to say the doors won't make a clicking sound even when locked (press the lock button a couple of times to see what that's like), but if the doors aren't locking when you put the car in gear, that's a major clue. That tidbit of information will help them find the problem.


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## Black Tammy (Jul 8, 2019)

ChevyGuy said:


> I confirmed this last night. The only thing I can personalize is the unlocking. Now, that's not to say the doors won't make a clicking sound even when locked (press the lock button a couple of times to see what that's like), but if the doors aren't locking when you put the car in gear, that's a major clue. That tidbit of information will help them find the problem.


As of this moment, I'm still waiting for the verdict from the Chevy dealership where I took the car this morning. Apparently, they didn't get started on the diagnosis till almost closing time. The manager said that he told the mechanic to check the gearshift switch first so I'm hoping that will do the trick. Thank you so much for that idea and fingers crossed.


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## 375802 (Jul 9, 2019)

Black Tammy said:


> JUST bought a 2012 Chevy Cruze LTZ, a one-owner car and looks beautiful. After driving it for 20 minutes on the expressway, suddenly the doors locked and simultaneously it downshifted to low gear when I was driving approx 60-70 mph, which almost gave me a coronary. Now almost a week later, I've experienced the same thing going at a high speed, and at a low speed. What the heck? Should I get a diagnosis of electrical system? And transmission check? has anyone had these specific symptoms?


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## 375802 (Jul 9, 2019)

Maybe going into "Pursuit" mode?


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## Black Tammy (Jul 8, 2019)

They finally found my problem. The fuse box melted a wire which in turn messed up all the codes. Does this make sense? The mechanic feels certain this will fix the problem.


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## plano-doug (Jul 1, 2015)

Black Tammy said:


> They finally found my problem. The fuse box melted a wire which in turn messed up all the codes. Does this make sense? The mechanic feels certain this will fix the problem.


When I read your initial post, my first instinct was that you had some sort of wiring problem - ie, an intermittent connection - that was causing the problem, but couldn't be more specific than that. 

That your mechanic found a melted wire at the fusebox and says that's the source of the problem is entirely believable.

Besides repairing/replacing the burnt wire, whatever caused it to overheat needs to be determined and fixed as well.

HTH.

Doug

.


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## Black Tammy (Jul 8, 2019)

I'll ask about that when I pick it up. Thank you, Doug.


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## ChevyGuy (Dec 13, 2014)

Melted wires can do a lot of odd things. The real question is if the problem goes away. You'll be the first to know.


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## Jaycruze12 (Jul 21, 2019)

I have a 2012 eco and this exact thing has happened twice to me. The first time I was on the freeway going about 75 miles an hour. Me and my kids were coming back from Utah and It was around 1 am. Kids were sound asleep so I was just enjoying the peace and quiet. Then all of a sudden chaos begins.... all the doors unlock, lock, unlock and lock and my power steering light comes on and then my transmission slams into first gear. The RPMs pegged well past 8000 so I put the car neutral, hit the brakes as hard as I could without losing control, pulled on to the shoulder and listened for something to break in the engine. The RPMs stay at 8,000 until about 20 miles an hour. All this happened in a matter of 3 seconds. The second time it did it I was only doing 35 miles an hour and the door locks didn't unlock and lock again but it did slam into first gear but my stabilitrak service light came on second before it happened. I took it to the dealer and they couldn't find anything wrong and couldn't explain why. I got the impression nobody there really believed me so here I am..


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## Rogers0639 (Jun 17, 2021)

Jaycruze12 said:


> I have a 2012 eco and this exact thing has happened twice to me. The first time I was on the freeway going about 75 miles an hour. Me and my kids were coming back from Utah and It was around 1 am. Kids were sound asleep so I was just enjoying the peace and quiet. Then all of a sudden chaos begins.... all the doors unlock, lock, unlock and lock and my power steering light comes on and then my transmission slams into first gear. The RPMs pegged well past 8000 so I put the car neutral, hit the brakes as hard as I could without losing control, pulled on to the shoulder and listened for something to break in the engine. The RPMs stay at 8,000 until about 20 miles an hour. All this happened in a matter of 3 seconds. The second time it did it I was only doing 35 miles an hour and the door locks didn't unlock and lock again but it did slam into first gear but my stabilitrak service light came on second before it happened. I took it to the dealer and they couldn't find anything wrong and couldn't explain why. I got the impression nobody there really believed me so here I am..


my 2012 is doing the same thing except it’s almost nonstop. It only starts to act up once the engine is warm too. I can drive just finebut once the engine gets to it’s halfway thermostat point I’m in trouble. Did you ever find a solution? Transmission or sensor??


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## Blasirl (Mar 31, 2015)

Rogers0639 said:


> my 2012 is doing the same thing except it’s almost nonstop. It only starts to act up once the engine is warm too. I can drive just finebut once the engine gets to it’s halfway thermostat point I’m in trouble. Did you ever find a solution? Transmission or sensor??


Welcome aboard!

Jaycruze12 has not been online here since he posted that, but @Black Tammy has and she might be able to help

Don't forget to introduce yourself and your Cruze here.

Remember to vote:

Spring 2021 MOTM Voting Thread
Spring 2021 COTM Voting Thread

and then consider running for either or both in the next run!


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## Rogers0639 (Jun 17, 2021)

_@Black Tammy do you have any clue what’s going on?_


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## Selena2686 (Aug 13, 2021)

Did any one find a solution to this issue. I would really hate to sell my car. Im having this exact issue an had the tcm fixed but i still get the same issue. Im thinking now its more of a electrical problem.


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