My dryer will not shut down it only stop if I

do you have heat?does it stay hot while in coll down?if so your heating element is grounded,open the door,look up and remove the two screws holding the top panel in place,pick top panel up just a little and move it to the left that should remove the top panel, put it on cool down or no heat and run it,if the heat stays on this is your problem the element is sagging and touching the metal cover around the element,the way the timer works is on timed dry it counts down like a clock until it turns off when on more or less or auto same thing the dryer starts,the heat comes on and when it hits temp. the heat shuts off when the heat is off the timer will advance to off when the heat starts again the timer stops,if the element isn't grounded then you still could have a bad element there are two elements in your dryer if one is broke the timer won't advance or some have only one element so if the timer doesn't advance you probably have no heat or a bad cycling thermostat or a bad sensor up front where the lint filter is.you'll have to check them with a meter.first thing to check is the heater located behind the drum.

Oh I can't think of the name of it right now but the whole knob assembly inside needs to be replaced. It's like a timer its integrated into the knob.

if you have it on time dry and it doesn't count down the timer is bad but it should stop when you open the door unless you have a broken door switch too,just open the door and push in on the switch with your finger,it should make a clicking sound,if not the door switch is also broke,if you have the timer on auto or more or less then it won't move without heat.on auto the heat comes on when the dryer reaches temp. the heat shuts off and the timer will advance a little,then the heat starts again and the timer stops,it will do this until the clothes are dry by using a sensor instead of time.

that model number doesn't come up,you sure that isn't the serial number?also does the dryer have heat,when you run it on time dry the timer just counts down like a clock,when on auto or more or less the heat comes on until the dryer heats to temp. the heat shuts off and the timer will advance,when the heat comes back on the timer stops moving,it will do this until the clothes are dry,if you do have heat you could have a bad sensor or a bad cycling thermostat but you'll have to check it with a meter.send the model number and i can help you better.

does the element come on at this point ?
I'm not sure if you tried this already or not, but i would unplug the unit and wait a min and plug it back in and see if it resets and then works again . you could have had a power surge .

what are you running it on?auto or more or less,if so the timer will not advance to off without heat,usually the heat comes on,the dryer heats up until it reaches temp.the heater shuts off and then the timer will start to advance to off,when the heat comes back on the timer will stop advancing and the heat will come on,it will do this until the clothes are dry,so no heat the timer will not move,now if you put it on time dry the timer should count down no matter what just like a clock.if you open the door and look around the opening where you put the clothes in you'll see a tag with the model number send this and i can help you.

if it's not advacing in time dry you have a bad timer,that timer should count down no matter what the dryer is doing,if you have it in auto then it could be no heat,when it's in auto or more or less cycle the heat comes on and the timer won't move until the heat shuts down,when the heat is off timer advances,when the heat starts the timer stops,it will do this until the clothes are dry and then timer will shut off but in timed cycle,timer isn't counting down get a new timer.

if the dryer is running and then the motor stops when it gets hot it sounds like you have a bad motor.when was the last time you cleaned out the dryer and vent line?also i need the model number,on some kenmore dryers they have even heat that can cause this to happen if it's in your machine the timer will count down faster than normal and shut down ,or you could have a bad thermister so send the model number and i can check it out for you.

replace the sensa board and make sure the wires on the sensors are ok

Your machine may have a feature called wrinkle guard or wrinkle shield, which basically keeps tumbling the clothes without heat to prevent wrinkles from setting in. Turn that feature off and see if that does the trick.