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Transmission

Andrew14m

By Andrew14m
in Ask A GM Technician

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Andrew14m New Member

Andrew14m

Posted
Posted

alright, well i just recently bought my truck. its a 1999 gmc sierra 1500 z71 with the 5.3 4wd. and when its cold outside ( i live in upper michigan) the tranny shifts at a higher rpm than normal, when the truck warms up tho after awhile it shifts normally. like an example would be, today after work at 11pm i had my truck running for about 8-10 minutes, when i went to drive it shifted at like 10 or 15 mph or whatever but when i hit like 25 or 30 it still hadnt shifted again and when it did shift it was at like 2500 -3000 rpm whic isnt normal becuz when its warm it'll shift at a much lower rpm than that. i was wondering if this is a sign of my tranny going to crap or a sensor or something because my dad said he thinks those trannys have sensors. if u have ne questions that will help you understand better please ask. id really like to figure this out. THANK YOU!!!

bobcat5544 Enthusiast

bobcat5544

Posted
Posted

In most cases this is normal. When the trans temp and the engine temp sensor tell the PCM that the fluids are cold the PCM will delay the shift.

 

Two reasons for this.

 

1st when oil is cold it moves slower. With higher engine RPMS it creates more pressure and flow. If it didn't do this then the trans whould take for ever to shift or just slip.

 

2nd the PCM is also trying to get the engine and trans warmed up quicker.

KB06YUKONXL Enthusiast

KB06YUKONXL

Posted
Posted

Your trans ATF is cold and thick like posted by the tech. If you want you can replace the DexronIII you have in that trans with Mobil1 Synthetic ATF or DexronVI which is also a synthetic and will have less of a tendency to do that because the synthetics flow better when cold.

StoneyPgh Enthusiast

StoneyPgh

Posted
Posted

It's also possible that the tranny filter is in a semi clogged condition and the

cold trans fluid is having difficulty passing through it.

 

The first thing I would do, if it were my truck, is to have the tranny serviced,

especially a new filter.

yfz450dk Enthusiast

yfz450dk

Posted
Posted

If you look in your manual, Like I did a few days back, it explains the transmissons cold weather warm up routine. It shifts at a higher RPM, to warm up the transmission faster. You have nothing to worry about, my 06 with 6500 miles does it.

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