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Discussion Starter #1
Hello all,

I found several threads on this and have a question on some items I can check myself. First off, I do not have any codes and the live running diagnostics show everything as ok. The issue is, in the morning, I do not even notice an issue, however after driving for about 30+ minutes on the highway, when I get on a road where 1-2 & 3 gears get used the most, I start to notice hard shifting. I tend to notice it during lunch or on my way home right away before I get on the highway but never in the morning when I start the car after 12 or so hours of it being off. It appears something is either jacked up with the trans and I am beginning to notice it, or perhaps something electrical?

I was going to check some obvious things first that I saw in the threads below:

http://www.yourcobalt.com/forums/problems-service/29979-bcm-pcm-locations.html

http://www.yourcobalt.com/forums/problems-service/29709-2008-cobalt-ls-problem-acceleration-lack-power-hard-shifting.html

My question is (and as silly as it may be), SHOULD I unhook the battery to perform these operations? Or is it perfectly safe to remove the ground to clean it off while the battery is still connected? I do not want to accidently fry any sensors or electronics in the vehicle.

I assume it is safe to pull the TCM fuse at least while the battery is connected to check for corrosion? Clearly, I intend to have the vehicle OFF while performing these tasks.

That's all for now. If anyone else has advise on other things I can check without having to have someone dig into the trans please let me know. I have maintained all maintenance to the mile (+/- 5K on major services) and have 129K miles currently. I got the vehicle brand new in 06' (I have an 07' model). I had a 2nd trans filter & flush about 10000 miles ago so I should still be good there. I have replaced the fuel filter, cleaned TB, new plugs, clean filters, clean MAF and the car itself idles VERY smooth.

Thanks! :)
 

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Always safer to disconnect battery, that way you can't accidentally short anything.

Your transmission is acting like it is low on fluid, I would check fluid levels first. Bring car to operating temperature then put it on a hoist while running and remove the level plug. Oil should drip out if it is properly filled. It will gush out if it's over filled.
 

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Discussion Starter #3
Oh how I wish these newer cars had transmission dip sticks! :cheesy: This would normally be the first thing I check, along with the fluid color to check for any sort of burning. While I do have a ton of tools at my disposal, a hoist is something I do not have... :sad:

I'll disconnect the battery and check the easy stuff after work one night, I will probably have to stop by the quick care place at the dealership on Saturday and have a buddy check the fluid level for me real quick and maybe top it off if its low. I did check, my last full fluid exchange & filter was actually 16000 miles ago. Never had issues until about 4 weeks ago (when I first noticed it when it got really hot outside).

Perhaps a bad gasket causing a very slow leak at high speeds? I have not seen any fluid spots in the space I always park my car at night.

Thanks for the feedback!
 

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Hey Sly,

This is weird, cause im pretty much having the same problem I think.... for starters I have a 2007 cobalt ss 2.4l sedan model I have recently changed my fuel filter, fuel injectors, and upstream o2 sensor. now my car is giving me a "service traction" message and "traction off" message. my car seems to "clunk" into drive from park... and even driving switching from 1st to 2nd... if I dont have the warning message, my car drivers perfectly fine... Im about to bring my car in. wondering if you have had any luck on this? or ideas because I do so.
 

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You don't have the same problem, you're losing GMLan communication. Try disconnecting both blue connectors from the BCM and re-connecting a few times to clean them out.
 

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Discussion Starter #6
Yeah, not the same issue Ownag. Shifting between Park/Neutral/Drive is perfectly fine for me. I never get any sort of "traction" errors either. I am sure the average individual would not even notice anything wrong with my car. I just happen to be very tuned into how it should feel after having it since I got it brand new back in 06.

Speaking of the issue, I am taking it into a Chevy dealership tomorrow to have someone check the level for me to either confirm if I have a small leak and low fluid is the culprit, or to rule that out as being a cause. I will keep everyone posted of what is found.
 

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Discussion Starter #7
Well, the level was only an 1/8 quart low. They topped it off for me, but certainly not enough to cause the issue and I did not really notice much of a difference driving it home as it had been warmed up for quite some time by then.

Anyone have any ideas I can look into myself without having to take it in to have a transmission technician look at it? I am going to check the TCM fuse and ground connections this coming weekend. Other than that, not sure what else I can check on my own.

What sucks is, its bad enough where I can notice it after so many years of driving the vehicle. However, it is probably not bad enough for someone else to notice it who has not been in the car before it started having the slightly hard shifting issue. :/
 

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There are 2 TCM fuses although the one in the BCM should be called GMLan. Check for pitting our replace outright.





You may also want to disconnect both blue connectors from the BCM and re-connecting a few times to clean them out. No harm in trying and it's cheap.
 

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Discussion Starter #9
I checked the ECM/TRANS fuse last weekend... was reading 4 ohms and looked alright. I cleaned it off with a wire brush and put it back in.

Any tricks to ripping off the BCM fuse cover? It felt like I was going to snap it in half... lol. I have ripped off the door panels before to fix speaker and window issues and I have spare clips for those, but I do not have anything for the BCM cover (unless it does take more force and I am more than safe just going for it)!

I suppose it is worth a shot! I might just outright replace the fuses with the spares sitting in both boxes.
 

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Yeah just the regular GM clips. You need to pull from the bottom in order not to break the top plastic tab.

 

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I know your problem is different then mine (to an extent) but test your map sensor, my problem was the map sensor, after that was replaced, tcm reflashed, and cleaned maf sensor, problem is now gone.
 

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I know your problem is different then mine (to an extent) but test your map sensor, my problem was the map sensor, after that was replaced, tcm reflashed, and cleaned maf sensor, problem is now gone.
It's worth a shot. I ended up cleaning the ECM Fuse (it was somewhat dirty) and did clean off the grounding lug. It seemed to smooth things out a little bit, but I can still feel the problem, although it is worse on hotter days than colder ones it seems. When people are in my car they don't really notice it so I am sure it's because I know the feel of my car very well. I'd just like to find out what it is before it gets so bad I'd have to rebuild the transmission. At the same time, its throwing no error codes and until the car warms up its not very noticeable (and even then, not nearly as bad as some cars I have been in).

Any procedures on checking this thing? Or will a shop need to perform this check?

I'll clean my MAF sensor over the weekend when I have a chance. When I cleaned by TB out last year I skipped cleaning the MAF sensor. My car idles VERY smooth, not sure how the MAF would effect my trans shifting. But then again, I have seen stranger... lol.
 
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