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Discussion Starter · #1 ·
I have an 04 Trailblazer LS 4x4 that is all stock and around 170,000 miles. I have a sudden jerk/shudder anywhere from 45 to at least 75 MPH. I have checked the codes and the only ones are a coolant temp too low and secondary air injection system code. I thought it may have been due to old transmission fluid so I changed the filter and flushed by starting up the vehicle and leaving one of the cooler lines off until new fluid came out. This had very little impact on the shuddering. I tried the brake switch test and so far the shuddering stops when activating the brake switch. I have tried keeping the brake pressed and shifting into drive and lightly accelerating and no shuddering or surges are noticed. I am just looking for some guidance for next steps.
 

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1. Fix the low-temperature problem. Likely need a new thermostat.

2. Fix the air injection problem.

Having fixed those two known problems, the shudder may go away on it's own. If not, the problem is almost certainly in the torque converter clutch, or the control system for the TCC.
 

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1. Fix the low-temperature problem. Likely need a new thermostat.

2. Fix the air injection problem.

Having fixed those two known problems, the shudder may go away on it's own. If not, the problem is almost certainly in the torque converter clutch, or the control system for the TCC.
My code P0128 over the years came on three times. Each time it was the CTS. Shuddering when the TCC is applied can easily be called by a mild engine miss also.
 

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Discussion Starter · #4 ·
Thank you for the information. I had the parts to fix the PO128 code on the way and will try to get to that next week probably but I was just curious what would be the next steps to troubleshoot torque converter related issues?
 

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Thank you for the information. I had the parts to fix the PO128 code on the way and will try to get to that next week probably but I was just curious what would be the next steps to troubleshoot torque converter related issues?
Determine if it has trans codes, particularly P1870, and if it has an engine miss.
 

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I have an 04 Trailblazer LS 4x4 that is all stock and around 170,000 miles. I have a sudden jerk/shudder anywhere from 45 to at least 75 MPH. I have checked the codes and the only ones are a coolant temp too low and secondary air injection system code. I thought it may have been due to old transmission fluid so I changed the filter and flushed by starting up the vehicle and leaving one of the cooler lines off until new fluid came out. This had very little impact on the shuddering. I tried the brake switch test and so far the shuddering stops when activating the brake switch. I have tried keeping the brake pressed and shifting into drive and lightly accelerating and no shuddering or surges are noticed. I am just looking for some guidance for next steps.
Thank you for the information. I had the parts to fix the PO128 code on the way and will try to get to that next week probably but I was just curious what would be the next steps to troubleshoot torque converter related issues?
If you gently apply left foot on brake amd rpm jumps up a punt 200 rpm amd shutter goes away i would bet it’s a bad clutch in the lock up converter. My 04 had that problem from high 100ks to 220k when I blew head gasket amd let her go
 

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Those are emissions codes. They shouldn't effect the transmission.

My SAIS is totally disabled, and I never noticed any issues when my thermostat was stuck open.

Is the jerking repeating? Let's say the car is doing 55mph. Does the rpm gauge jump up and down? Even a little? Mine did this and I had a bad TCC valve in the valvebody
 

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Discussion Starter · #8 ·
I just replaced the thermostat and it did fail open but still need to test drive it. The jerking is worse some days and then other days almost none. It mostly occurs on the highway in cruise from 45 to 75 mph. The rpms may vary some but it is extremely slight
 

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I'd bet it's your TCC valve. Or a worn valve bore to be more specific. There is a replacement valve that should fix the problem.

It's a 20 dollar valve that replaces the troublesome pwm valve with a on/off TCC valve.

You need to drop the pan to do this. Fluid and filter change is recommended. Rock Auto sells a cheap kit with AcDelco trans filter and a new pan gasket.
 

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Do you a favor and watch this video from my YouTube channel.

Get on an open stretch of land, go exactly 50 mph, wait for the converter to lock up, and see if your issues match that of the video.

Make sure the open stretch of freeway is flat and don't use cruise control. You want to be in lockup at 50 and avoid acceleration or deceleration. Whether it's from the brake/gas or the slope of the road.
 

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Discussion Starter · #11 ·
Where is the best place to get this TCC valve kit?

I will have to take a drive and keep a closer eye on rpms but I do not think mine moved that much, seemed more consistent.
 

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I'd bet it's your TCC valve. Or a worn valve bore to be more specific. There is a replacement valve that should fix the problem.

It's a 20 dollar valve that replaces the troublesome pwm valve with a on/off TCC valve.

You need to drop the pan to do this. Fluid and filter change is recommended. Rock Auto sells a cheap kit with AcDelco trans filter and a new pan gasket.
You need to drop the valve body too.
 

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Discussion Starter · #17 ·
Thank you for all the good information so far. I will give the TCC valve a try. Is it just the mechanical valve swap or is there any software work required?
 

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It's just a valve swap purely mechanical. It is kind of annoying to do it with the valve body on.

The retaining clip needs to come off from the wrong side of that makes sense. Since it's upside down. It's needs to be bent/ manipulated etc.

Once that's done you're home free!

Also I punched a hole in my drain pan and replaced with a cheap dorman painted pan that featured a drain plug.
 

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Discussion Starter · #19 ·
I installed the valve kit but it did not go away, actually seems a little worse now. Engine seems to be running smooth with no issues. I am guessing the torque converter is on the way out….
 
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