Question about 2003 GMC Yukon Denali
My truck won't shift into third gear. But it does OK in 1st, reverse, and 2nd. My security light flashes on while driving as well. Please help ID the issue
Posted by Anonymous on
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Posted on Jan 02, 2017
no sound like 3 and 4 are gone.you will have to replace the tran . good luck
Posted on Apr 17, 2009
sounds like a modulator problem,make sure you have vaccume going to the modulator on the tranny, start the truck leave it in park pull of the vaccume line at the tranny , if its got fluid in it then its bad, and make sure you have vaccume too it!!!!
Posted on Jan 05, 2010
SOURCE: transmision starts out in 1st
Sounds like your transmission is in limp mode. This is a fault mode in which the
transmission either loses electrical power or the PCM deactivates all of
the electronics. The transmission will default to max line pressure.
The driver will have Reverse and 3rd, with manual 2nd available by
putting the gearshift in 2 or 1 (doesn't matter). 1st, 4th, and TCC
lockup will not be available. It will not hurt the car to drive it like
this for short periods, but use manual 2nd to get the car moving, and be
aware that the trans will generate more heat than normal while
operating in limp-home mode due to increased torque converter slippage
during 2nd gear starts and no lockup in 3rd gear.
The other from what you described, trans shifts 2nd to 3rd by itself in D or OD and locks the converter : ShiftA solenoid failed. Easy fix in the pan. Or a wiring problem from PCM to trans.. or PCM.
Thank you for using fixya and have your Safari scanned for the DTC codes that would indicate what issues your transmission is having to put you in to limp mode.
Posted on Sep 21, 2010
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