Will not shift into 4th gear

Tiny
DBAKER761
  • MEMBER
  • 2005 CHEVROLET TRAILBLAZER
  • 93,000 MILES
I have a 2005 Chevrolet Trailblazer with the 6 cylinder engine and 4L60E tranny. On way home from a trip the transmission would not shift into 4th gear (overdrive). 1-3 gears shift fine. No engine codes being displayed. Changed fluid and found no metal. Took to a local transmission shop and they are stumped. Shop advised that when they hooked up to the computer they advised they can see where the computer is sending the command to shift into 4th gear, but it's not happening. He advised if it was a clutch pack problem it would "neutral" out when given the command to shift into 4th, but the truck just stays in 3rd. Tranny shop is leaning towards computer or electrical, but still unknown. Any ideas?
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Friday, March 16th, 2012 AT 7:02 PM

8 Replies

Tiny
RASMATAZ
  • MEMBER
The computer might not be giving a command because a shaft speed sensor could be going out but not enough to trigger a code. You can try checking live data on a test drive or replace both the input and output shaft speed sensors
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Friday, March 16th, 2012 AT 7:29 PM
Tiny
DBAKER761
  • MEMBER
It's my understanding that on this model the shift solenoids are both activated in 2nd gear. If so doesn't this mean they are both good?
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Friday, March 16th, 2012 AT 7:35 PM
Tiny
TWO LANE
  • EXPERT
If they see that the computer is sending the signal to shift into 4th gear have they checked at the trans is the trans solenoid receiving that signal if so the would eliminate the wiring to the trans and at the trans what controls 4th.I would go more towards electrical but poss. Internal trans problem. I will look up the control circuit and see what controls 4th. And will get back to you.
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Friday, March 16th, 2012 AT 8:08 PM
Tiny
DBAKER761
  • MEMBER
That would be a great help. Thank you
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Saturday, March 17th, 2012 AT 10:15 PM
Tiny
TWO LANE
  • EXPERT
There is a TSB for your car but it doesn't help our situation
Ref num 00-07-30-022D
Affected models 1993-2005 GM Passenger cars and light duty trucks
no rev, second gear or fourth gear
replace reaction sun shell with more robust heat treated parts
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Sunday, March 18th, 2012 AT 2:56 AM
Tiny
DBAKER761
  • MEMBER
I thought about that but if the sun shell busted I would have metal in the pan but it was clean. Thinking about bringing it home from the tranny shop and taking a look at the wiring. How would I test to see if the transmission is getting the shift command from the computer. Do I need the Tech 2 for that?
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Sunday, March 18th, 2012 AT 5:27 AM
Tiny
TWO LANE
  • EXPERT
Yes you need it to accurate the sensors and see what is going on. That why you can actuate that sensor and check it see if in specs also you can check the pressures in the valve body so you can see if it is electrical or pressure problem.
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Sunday, March 18th, 2012 AT 6:53 AM
Tiny
DBAKER761
  • MEMBER
I appreciate all of your help. It did end up being an internal problem and the transmission was rebuilt. Thanks again
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Wednesday, March 28th, 2012 AT 9:59 PM

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