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Discussion Starter #1
I'm going to do my best to explain what is happening with my 2008 G6 GT with the 3.5v6. Sometimes when shifting from park to drive it will shift very hard into gear. Once in drive, it will continue to shift hard. When this happens the engine idle is different than normal and is much louder than normal. The car doesn't throw any codes for the CEL to come on. Funny thing is when I hook a code scanner up, it reads no codes like I said. But even with no codes present, if I select clear codes anyway, the engine idle changes and car starts shifting fine. I just want to reiterate that no codes show and the CEL light does not come on. This hard shifting will also reset itself if the car is left off for a period of time. Does anyone have any idea what this could be?
 

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I'm having the same issue with my 07 G6 GT, initially it will shift hard into the next gear if I accelerate with any urgency. I've also noticed a difference in noise when in idle
 

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I’ve been having same prb with my 05 GT, It will hard shift when u turn off the car and wait 5mins it goes back to normal, it’s a issue btw the pcm and bcm according what I been told, what I have done to help with the prb, I took off the transmission harness and cleaned it and applied derelict grease and also on bcm and pcm, so far it has work once in a blue moon it happens
 

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Discussion Starter #4
I’ve been having same prb with my 05 GT, It will hard shift when u turn off the car and wait 5mins it goes back to normal, it’s a issue btw the pcm and bcm according what I been told, what I have done to help with the prb, I took off the transmission harness and cleaned it and applied derelict grease and also on bcm and pcm, so far it has work once in a blue moon it happens
Can you provide details about the transmission harness and where you applied the grease? I wonder if this has anything to do with the transmission service bulletin that recommends replacing the transmission wiring harness. Is the transmission harness hard to get to?
 

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Hi,

Check and see if there is a TSB or recall that hasn't been done on your car. I had one done in 2015 that was related to the hard shifting.
 

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Discussion Starter #7
Can anyone tell me how to access the transmission wiring harness? I read there was a tsb at one point that said something about a wire touching a metal clip or something that could cause this. Is there a way to see any codes that aren't showing up on my cheap code reader? This car has never thrown a code the entire time I've had it.
 
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