1999 GMC Sierra Transmission question

Tiny
SOONER41
  • MEMBER
  • 1999 GMC SIERRA
  • V8
  • 4WD
  • AUTOMATIC
  • 122,000 MILES
I have a 99 GMC Sierra 1500 Z71 with 122k miles. Truck goes into drive fine but when it shifts from 1st to 2nd gear I lose a lot of power and no matter how much gas I give it it just wont go any faster until it shifts into 3rd gear and I have full power back. It had been doing this for a couple of weeks at random times and now the "service engine soon" light has come on. Do you have any ideas what it could be? Please dont tell me I need the transmission rebuilt.
Saturday, August 16th, 2008 AT 11:12 PM

3 Replies

Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
Hi there,

I would start with getting the set fault codes read, there is a problem with in the transmission and the more you drive it the worse it well may become, see what the code is and contact a transmission specialist before you do require a full re build, if it snot to late already.

Mark (mhpautos)
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Sunday, August 17th, 2008 AT 5:31 AM
Tiny
SOONER41
  • MEMBER
  • 2 POSTS
Thanks for your help so much. I got a diagnostic and it said "2-3 shift solenoid valve performance, Explanation - transmission in drive -ECM compared engine speed to vehicle speed inputs and detected an incorrect shift pattern, Probable causes - 1. Shift solenoid failure-Repair other codes first. 2. Open or short circuit condition. 3. Internal transmision failure."
Im gonna have somebody take a look at it tomorrow but i'm stressing over this and wondered what I should be looking for first? Somebody recommended to start out with a transmission fulush but I dont see how that would help. Thanks.
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Sunday, August 17th, 2008 AT 10:49 AM
Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
Hi there,

I would get the solenoid issue looked at first, they will have to drain the trans and change the filter anyway, get this done and you may fine that all is well, start here.

Mark (mhpautos)
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Sunday, August 17th, 2008 AT 5:13 PM

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