unfortunately thats not always the case,, if a sensor tells the car ecu if the engine is cold (to add more fuel/ air) or hot ( to send less fuel/air) and it sticks or fails and makes the ecu think the car is always hot then you wont get the right mixture to start the car first time when the engine is cold and there wont be a fault shown as the sensor is stuck in within normal sensor readings ( hope ive explained it ok)
