Sensor Diagnostics

Hello, I have a doubt with ECU error diagnosis . How does the ECU know that a sensor is not working properly?. Like in case if it is shorted to ground, not connected or if the sensor is showing a wrong value how does the ECU know that the value is wrong?. For example the intake air temperature sensor shows 20 degrees Celsius where the real temperature is 40 degrees how does the ECU know that this value could be wrong?. Most of the sensors are interlinked in a car so if air intake temperature sensor shows a wrong value is there any other way to identify that this is wrong. And same goes for other sensors like Coolant temperature, MAP, etc… how do they figure it out that they are showing a wrong value.

Normally this is done by setting a working voltage range (typically 0.5V to 4.5V) for the signal, and if the signal exceeds this voltage range for a specified period of time, then the ECU marks that sensor as invalid and either reports no data, or a preset default value for the signal.

What if the voltage reading is in the range but the value is wrong? Does the ECU have any way to figure it out?

Depends on the ECU, most that I have dealt with (aftermarket) do not have any plausibility checking (i.e. coolant temp cannot be -20 when the engine has run for X period of time) in their designs to handle this sort of a check. Some of the OEM ECU's do have this sort of validation, but it will have been modelled on a large number of engine to validate the data used.