So your vehicle won't start. What's the first thing that comes to mind? Battery dead? Starter motor worn out? Out of gas? Well, those are all reasons that make sense. But your vehicle may be refusing to start because one of its computers is being warned that to do so might damage it. Here's how that works.
You have lots of computers in your vehicle. They need to know the status of things so there are several sensors monitoring various things going on. These sensors send information to the computers that adjust the fuel and air mixture so you don't waste fuel. They know when things aren't quite right and prevent you from starting your engine if that's going to damage it.
Other sensors make sure the coolant is the right temperature, check to see you are not polluting the air and make sure other electronic components are performing their tasks correctly.
Here's an example of a sensor doing its job. Your engine needs oil to lubricate metal components so the friction doesn't damage them. Your engine has an oil pressure sensor that tells a computer called the Electronic Control Unit (ECU) if things are good to go or if there's something wrong, maybe the oil pressure is too low to keep things lubricated. If it is, it gives a signal for the vehicle not to start, protecting the engine.
Of course, the sensors can go bad, too, with some of the same results. And so someone has to figure out if it's the sensor that's failed or if it really has detected a problem. That is the challenge for technicians with specialized equipment to decipher the signs. If a bad sensor is found, it may need to be replaced. Sometimes a thorough cleaning can do the trick. In either case, your service facility can track down the problem and get you back on the road. Makes sense, doesn't it?