i have a 2000 gmc seria 5.3. i replaced the trans cuz of 3-4 burn up.and a few month after putting one in that i bought it goes into lock up intermitintly.. it seems when it is cold it goes into lock with no prob , but when warmed up it will not go into lock up.i took it in and had it scanned.
po151 o2sensor,i replaced,po300 random missire,said this could be caused by the o2 sensor gone,truck does not idel rough now.p1153 but is this another 02 sensor or is this caused by the one i replaced. p1380 i think this is the i pulled the wire when replacing ball joints. and p1810 code trans pressure switch,so i dropped the pan and replaced the switch, and filter,and it still does the same thing..will unplugging the battery enough to reset this code,and is there any other prob such as a fuse that could cause the to happen of not going into lock up.could the 4th apply piston do this,, any ideas the shop does not.and its hockey season so spending alot on fuel with the tran not going into lock up..
thanks

 

there are a couple of things that can keep a tranny from going into lockup, the first and most important is the brake light switch...this activates the lights and also turns off the criuse and takes the tranny out of lockup...other than that...check your electrical plugins and make sure they are making good contact

 

k thks i will check that out, i know the cruise controll works fine,but will check the brake light switch. will the coolant temp sendor doe this just seen it on you tube, and will this cause send a trouble code .is there a way to manaully cuz it to lock up to test it.such as hooking it up to a on off switch. thks

 

Ok.... I have done tons of reading on this. Mine has been doing this for now 4 years. Especially in the summer, it will sound as if the 3-4 is slipping. In the winter, no problems. I have narrowed it down to either the TCC solenoid, or the TCC piston. There is one forum write up where a guy explains that the TCC piston shaft needs to be updated to a slightly bigger one. What is happening is when it engages, it does not seal and loses pressure. And I know what you are feeling, ALOT OF FRUSTRATION!!! Lol well, I will soon tackle this and find out if it cures it. In the mean time, when mine starts to act crazy, I just tap the brake while on the gas to hear the TC lock up. If you have loud exhaust, you can certainly hear it by the RPM's.

 

mine does not sound like it is slipping ,it will not lock up.it does sometimes and other times it dont.when u hit the brake does ur converter lock up i never tried that maybe i will tonight and let u know if it does,but this has me stumped.at 50 rpm is usually aroung 1500rpm to 1700rpm when it dont lock uo it is like 2000 to 2200 rpm..if u fing out whats it is let me knoe and i will do the same tks for the reply.

 

just tried that with the brakes and nothing,, but i did noticed that if it sits for a few day in will jump jerks when u start it.no much do a little...

 

How many miles are on the tranny? I know ruffneck is right on the piston issue and that is an update that is done on rebuilds now....if you have some mileage on it it might need a rebuild

 

there is only about 70k on this tranny. i replaced it cuz i lost 3 and 4th clutches on the other one..if it is the tcc would it give a pressure amnifold switch code i think it was 1810 but i replaced that..and i dont know if this means anything but when it was hooked up to the comp they could not get a temp reading on the trans.they said it was cold outside but there should be a difference in the temp reading when he took it for a drive.

 

Im not sure. If the TC does not lock up like it supposed to, then this would cause alot of heat cause the TC is always slipping until it locks up. That temp reading could tell you alot.

 

The temp sensor for tranny temp is on the valve body....if it has gunk built up around it it will not read and will cause all kinds of weird shifting problems also