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2004 chevy trailblazer_ls
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Discussion Starter · #1 ·
My trans has been acting a bit strange lately. Under normal driving conditions(to and from work, no highway) the shift points are much higher than they used to be. A few weeks ago 1st to 2nd would shift @ 2 - 2300, now it's at 3500, same with 2nd to 3rd. Once 3rd engages it immediately goes into OD. To get it out of OD, I have to depress the gas about half way(much more than I used to). I don't think I've ever noticed being in OD cruising at 25mph through the neighborhood......

If I floor it from a stop, the shift points are 1st - 2nd 4800,
2nd - 3rd 4800-5000, OD kicks in once I stop accelerating. About where they always have been.

Is there a rpm/speed sensor that controlls shift points or ????

The trans has been flushed twice in the last 5 years, 90,000 on the clock...
 

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2003 chevy trailblazer_ls
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What was the last thing you did before this started?
 

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2004 chevy trailblazer_ls
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Discussion Starter · #3 ·
Last thing was the a/c clutch bearing. Before that - water pump, idler pulley and belt tensioner. Last trans flush was November 2008.

Could a bad fan clutch have this type of effect on shift points?
 

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2003 chevy trailblazer_ls
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It shouldn't. Have you cleaned the throttle body, and how long ago. Are you using Dex3 or dex VI in the tranny?
 

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2002 chevy trailblazer_lt
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Your shifting extremely low, a pegged out WOT shift should be right around 6K, if your WOT shift is at 4800 somethings definately screwy, it could be PCM related because the PCM is what commands the unit and tells it that its time to shift
 

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2004 chevy trailblazer_ls
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Discussion Starter · #6 · (Edited)
Forgot about the throttle body cleaning.... Did that 2 weeks ago also, 3rd time in the 5 years I've owned it.

Dex 3 was used on the last trans flush...
 

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If you have no CEL or anything its Def a PCM issue, the PCM has to meet a certain set of variables and checklists before it will command a shift, and since its shifting out of its programmed commanded shiftpoint of 6K somethings wrong with the electronics, the transmission itself has nothing to do with commanding shifts, it just does whatever the PCM tells it to do
 

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Discussion Starter · #8 ·
No CEL, but I have not had it checked for any codes. I'll have that checked this evening, somewhere.....

If it turns out to be the PCM, could I send it to PCM4Less for tune or do you think it would need to be replaced?

Thanks for the quick replys, I appreciate it!
 

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Discussion Starter · #9 ·
Just got back from having the codes checked.... Nothing.

Guess it needs to go to the trans shop :worried:
 

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Its not a tranny issue dewd, its a electronics issue

at WOT from 1st to 2nd what MPH are you at

The PCM commands the tranny to shift after meeting a set speed or a set RPM, the RPM variable is obviously not being met if its shifting at 4300 and the programmed shiftpoint is 6000

With my 3.73s WOT the top of 1st is like 48-50mph something like that right before the shift, theres always the possibility that its just your gauge cluster acting up and the tach is reading inaccurately
 

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Discussion Starter · #11 ·
WOT 1st to 2nd shift was at ~49mph, rpms were just over 5000.

So if this something screwy with the PCM, would a PCM4Less tune fix it or is a new PCM in my future?


Thanks!
 

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Do you have 3.73s? Ide be more apt to say the guage cluster is funky then anything serious being wrong. a PCM failure is a rare occurance and from what ive seen both on here and in person, the guage clusters on these things especially the tachs more then anything go crazy
 
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