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Hello, I have a 2001 Sierra 2500 HD. The transmission is leaking quite a bit and throwing P0748 code. It is in limp mode. I clear the code by it reappears instantly. I am wondering if i add fluid if it will fix this problem so my plan was to change the screw on filter and add fluid.

The problem is the cold reading on the transmission dipstick for "cold" is at the top range of the hashmarks so Im wondering how do i go about knowing how much fluid to add.

Ive come to understand through read that checking fluid level while how is the best way to go but im wondering how to get it hot while its limping. Is it safe to drive it around in limp mode til it heats up a bit?

Im just an amateur looking for the best way to proceed.

Thanks.
 

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Where is it leaking? I would address the leak first. Then I would drain the pan, change the spin-on filter and add about 7.4 quarts of ATF and see where you’re at on the stick. You want it up to at least the “cold” marking on the stick before you do a hot check. On my truck I always just set the parking brake and let the truck idle in drive to get up to temp to check the level hot (160-180°F). Make sure you run the shifter through the gears, R-N-D several times to ensure that the valve body is primed and full of fluid before you check the level hot.

Being an 01, you don’t want to use Dex 6. I would use a generic Dex III type fluid or TES-295. I wouldn’t recommend throwing money at TES-295 until you see if adjusting the fluid level with some cheap Dex 3 solves your limp mode issue.
 
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