Fan jump right up then machine stop

Hello, my prusa i3 is acting wired again. Some time during printing in the temperature graph, the line indicate the extruder fan jumps way up, then the machine stops. Before this happens, I could smell a bit out rubber over heated like a burning tire smell. But I could found nothing on fire, What could have caused this and how to fix it and how to recovery from it? Thanks.

Edited 2 time(s). Last edit at 02/08/2018 06:50PM by rich1812.

There is an extruder fan that should always be running at 100 % at all times and when it fails hot ends plug up and extruder motors click and even shut down. Then there is a second fan that blows onto the part to cool it during printing and its % is adjustable for different layers and bridges etc. When this fan fails sometimes nothing happens or the part may look melted depends on settings and temperatures but it won't shut things down. The main things that shut it down are temperatures detected as too high or low or not reached when expected. Check,test,inspect or replace the hot end thermistor and make sure it has good contact with the heater block not sitting in mid air some hot ends actually clamp them to the block others use tape. If your machine is set up in firmware for PID control perform that operation to tune the heater. Also test the heater cartridge itself to make sure it is good and where the wires connect to the board are tight. A good heater will have a resistance of a few ohms when measured with a meter if it is open infinity replace it. The burning smell could be a bad fan bad heater connections or burnt filament if hotend is not cooled.