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Former Owner of a 2005 CTS
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Discussion Starter #1
Yesterday when I took the car out, I noticed that once I got around 40-50 miles an hour, the car seemed to be having an issue while it was shifting. The shift was harsh, and if you hold it at a certain spot, it seems to be surging and jerking a bit, almost like it's trying to do something (maybe shift), but is struggling to achieve it. You can visually see the jerking in the tach as well. It will jump a bit when it's acting this way.

I thought I had a flat tire when I felt it at first, but right once you let off the accelerator, or give it more gas, the problem goes away. (and obviously, no tire was flat)

I'm assuming it's transmission related. No transmission or engine related codes, transmission fluid and filter were changed within the year.

Any ideas?
 

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'05 CTS-V
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7,969 Posts
Does the problem occur at actual highway speeds (55-75mph)? Hopefully you're not doing 40-50mph on the highway! :p

Does it behave the same if you shift out of D into one of the other gear positions (4 or maybe 3)?
 

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2007 CTS 3.6 >129k miles
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535 Posts
Hmm. It certainly sounds like a trans issue. Given that the fluid/filter were changed I would assume no problems there unless the fluid level is not correct, but unfortunately checking it is not as easy as pulling a dipstick! Several possible causes, and I would start by verifying that the trans can perform manual shifts without problems (both up and downshifts through all gears). Assuming manual shifting works, the following info from the FSM provides other things to explore.

DEFINITION: Harsh shift feel - an unacceptable quick gear change occurs.
Check ------- Causes
Pressure Control Solenoid
-------  Damaged O-rings
-------  Contamination
Output Speed Sensor
------- Open or grounded circuit
Input Speed Sensor
------- Open or grounded circuit
Throttle Position
------- Open or grounded circuit
Forward Clutch Assembly
-------  Damaged or worn clutch plates
-------  Damaged or cut piston
-------  Damaged or stuck ball check valve
Control Valve Body Accumulator Assembly
-------  Accumulator piston stuck
-------  Stuck or missing ball check valves
Fluid Pump
-------  Pressure regulator valve stuck
-------  Pressure regulator valve spring
-------  Line boost valve spring
-------  Line boost valve or bushing stuck, damaged or incorrectly assembled
-------  Fluid pump screen assembly plugged or damaged
-------  Fluid pump rotor guide omitted or misassembled
-------  Fluid pump rotor cracked or broken
-------  Porosity in fluid pump
-------  Fluid pump surfaces not flat
-------  Excessive fluid pump rotor clearance
-------  Pump slide seal out of location
-------  Pump vanes damaged
-------  Pump slide spring damaged
Inspect for active transmission DTCs
------- Transmission DTC default action active
 

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Former Owner of a 2005 CTS
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71 Posts
Discussion Starter #4
Does the problem occur at actual highway speeds (55-75mph)? Hopefully you're not doing 40-50mph on the highway! :p

Does it behave the same if you shift out of D into one of the other gear positions (4 or maybe 3)?
I should have worded that differently. I meant that as i'm accelerating through around 40-55 it starts to surge a bit and jerk, then after that point, 60-70 rides normally, with an occasional jerking. But the problem is definitely noticeable when I'm around 40-55 mph.

I didn't try to shift it out of position, but I'll try and see how it reacts.


Hmm. It certainly sounds like a trans issue. Given that the fluid/filter were changed I would assume no problems there unless the fluid level is not correct, but unfortunately checking it is not as easy as pulling a dipstick! Several possible causes, and I would start by verifying that the trans can perform manual shifts without problems (both up and downshifts through all gears). Assuming manual shifting works, the following info from the FSM provides other things to explore.
By manual shifting you mean shifting through PRND432? I don't think I mentioned this in my first message, but everything up until I get to around 40-55mph is smooth. I don't really notice it shifting up until now, at around that point. And like I said, it almost feels like it's either trying to go in a gear, but cant get into it, or is getting into a gear and then dropping out of it rapidly. It feels like it's trying to do something, and not succeeding and trying over and over again until I give it more gas or stop trying to give it gas. I appreciate the input, and the information!
 

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2007 CTS 3.6 >129k miles
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535 Posts
By manual shifting you mean shifting through PRND432?
I was referring to sport mode, where the driver determines the shift points.
 

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Former Owner of a 2005 CTS
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71 Posts
Discussion Starter #6
I was referring to sport mode, where the driver determines the shift points.
I'll have to look into that. I wasn't aware that was what sport mode did on these cars. How does the driver determine each shift point?
 

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2007 CTS 3.6 >129k miles
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535 Posts
When you move the lever to the right you enter sport mode. The trans then works like a manual trans, and you push the lever forward to shift up, pull backward to downshift.
 

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Former Owner of a 2005 CTS
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Discussion Starter #8
When you move the lever to the right you enter sport mode. The trans then works like a manual trans, and you push the lever forward to shift up, pull backward to downshift.
I'm thinking I don't have this lever that we're discussing. The only sport mode I know of is the "S" inside of a gear, that is a button next to the shifter.
 

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2007 CTS 3.6 >129k miles
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535 Posts
Hmmm. I assumed that all 2004-2007 CTS had the Driver Shift Control (sport) mode where you just move the shift lever to the lower right side (see diagram from OM) in order to control the shift timing. Apparently this was not available until 06 (???)
576850
 

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Former Owner of a 2005 CTS
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Discussion Starter #10
Hmmm. I assumed that all 2004-2007 CTS had the Driver Shift Control (sport) mode where you just move the shift lever to the lower right side (see diagram from OM) in order to control the shift timing. Apparently this was not available until 06 (???)
View attachment 576850
That's what I was thinking. Nope, don't have it on my '05.

Had mechanic take it for a ride today, and confirmed that the transmission was slipping.

Unfortunately looks like it's nearing time to trade in, but we'll see.
 

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2007 CTS 3.6 >129k miles
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535 Posts
That is unfortunate. Of course, you could try one of the miracle trans supplements to see if it helps any... I wouldn't expect much but I have used Prolong trans treatment in the past and it helped smooth out shifts in a Buick LeSabre! YMMV
 
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