Shifted Into Reverse While Going 45mph in Automatic

chevrolet
rpm
transmissions
cobalt
fuel-economy

#1

I’ve taken my car to two mechanics now, and they both came up with completely different diagnoses for my car, so I’m hoping someone here might have some wisdom to share. The car is a well-maintained 2007 Chevy Cobalt LS automatic with 84K mi.

Don’t ask how or why, but I accidentally shifted this automatic into neutral and then reverse while traveling forward at 45mph. I immediately shifted back into neutral and then drive, but my car immediately went into “limp mode”. I coasted into a gas station, turned it off, turned it back on, and then I was able to drive it home without issue.

The next day on my normal route to work I felt like I was having to press the gas harder, and the RPM’s looked a little higher than usual. I checked the fuel economy, and for some reason I was averaging 15mpg. This is a car that has consistently gotten 30mpg+ ever since I’ve had it, so that was a drastic drop.

The first mechanic I took it to quickly said that based on my story, the sluggish acceleration, and the drastic drop in fuel economy, the clutch pack for my first gear was most likely burnt, and they would need to rebuild the transmission for $2,700.

The second mechanic drove the car around, check for fault codes, checked fluids, cleaned the air filter, etc and concluded there is absolutely nothing wrong with the car after having 3 people look at it over 2 days. They said it shifted fine when they drove it, and they were confident my transmission is sound. They said the dash displayed “ice possible” in 50 degree weather today, so their theory is that my dash had a little computer-freakout following the “limp mode” episode. They advised me to fill the gas tank and record my own fuel economy to see if I’ve actually experienced the drastic drop to 15mpg or not. The car is still at their shop, so I haven’t had a chance to do this.

I’m honestly not convinced either mechanic is right, so I’m posting here to see if anyone else has other ideas for what could have gone wonky after my stupid shifting mistake.


#2

The second mechanic was obviously wrong.

The first offered a plausible explanation. I’m not a tranny expert, but his explanation fits the symptoms.

Guys? What say you?
I miss transman.


#3

I’m not too sure of either of these diagnoses. I think most modern transmissions, which are electronically controlled, prevent actual engagement of reverse with the car moving forward at such a speed. But I agree with @"the same mountainbike"‌ on one thing: Where is @transman618‌ when you need him?


#4

If your dash was saying “ice possible”, you may have another coincidental problem–it could be the sensor that monitors the incoming air to the engine is flaky, which if it was reading low would cause the engine to run rich and drop your fuel mileage. Is your check engine light on? Have the ECU and transmission control module been scanned for trouble codes? Normally something like this would set a fault code.

If the transmission shifts normally and behaves no differently than it ever did, it’s hard to imagine the fault lies there, but not having the car in front of me to examine, it’s hard to say.


#5

Your car will not engage reverse when going45 mph so nothing should have happened to the transmission. If you car has gone into limp home mode, that would explain your poor gas mileage. Is your check engine light on while the car is running?


#6

Has the computer been reset?
I would do that first and cross my fingers.
Were there any unusual sounds or jerking when you hit reverse?
If not I really doubt there was any mechanical damage.
I think the second mechanic is right.
The sudden onset of multiple symptoms suggests a computer problem.


#7

I would tend to agree with @circuitsmith. But I wish @transman618‌ was around to give us a definitive answer (what happened to him, anyway?). I cannot imagine the computer in a car that modern would allow a shift to reverse when the car is moving forward at any appreciable speed.


#8

nothing is wrong with the tranny. focus on your mpg. unhook your battery and rehook it up and see if everything resets?


#9

A variation of @gdawgs’ suggestion: Try removing BOTH battery clamps and holding them together (c-clamp or vise-grips) for an hour, then reconnect. A long shot, but easy.


#10

Thank you everyone! The 2nd mechanic thought to do some computer-resetting (not sure exactly what) before I arrived to pick it up this morning, and the mpg is back to 30+ mpg! I am so relieved I didn’t get the transmission rebuilt or replace the car! And thank goodness my car is smarter than me and prevented me from doing damage when shifting into reverse.

I’m taking it on a 6-hr round trip Sunday, so we’ll see how it really does then. Crossing my fingers nothing bad happens.

Thanks again for all your input. You all are great!


#11

Glad you got it working again OP. Assuming all problems are resolved and there are no current diagnostic trouble codes being reported, and the check engine light is off. Next time you take it in to the shop for routine maintenance, the intake air temperature sensor (IAT) should be checked for calibration. The ECM uses this – besides informing the driver of ice on the roads – as a parameter for calculating injector pulse width to maintain the correct air to fuel ratio.


#12

Thanks GeorgeSanJose, that’s good to know, and I’ll mention this at my next oil change. There were no lights on my dash, and the computer didn’t show any fault codes. I hope I’m in the clear, but I’ll be coming back here with updates if not! :slight_smile:


#13

I did that on a 71 pickup as the shifter in-dent plate was worn doing about 25 MPH. The only thing that happened was I heard a clunk and the engine stalled. Put it in neutral and started it back up and no problems.