Part 2: Computers in your car!

This week we’re looking at another pivotal role the ECU takes on, managing the communications bus.

Bus? I don’t take the bus!

No, you may not, but almost every electronic control, sensor or monitor in your car does, your electric window controls, electronic mirror controls and even your dashboard are all reliant on this bus!

Obviously we’re not talking double deckers here! A “bus” is a term for a data highway along which electronic information can travel. By having a range of sensors placed around your car, all connected to the same communications bus your dashboard (or instrument cluster) is able to read information from all of these sensors simultaneously and give you a simple, unified view of all the components in your car.

How does this work? The ECU is connected to the communications bus and is already monitoring every conceivable aspect of your vehicles performance and state from a variety of different sensors. The ECU sends out small packets of data a few times each second across the communications bus, reflecting the values the sensors are reporting. The dashboard controller knows which of these packets to look for, when it finds one it simply adjusts the display or gauge on your dashboard to indicate the value it has received. Repeat the same process amongst a handful of sensors and you have a continuously updated dashboard display!

What else is all this data used for?

Ever seen a mechanic hook up a laptop to your car for a quick health check or to diagnose faults? What are they reading on screen and how on earth does it help?

Every time your car senses a fault of any kind (even if you don’t!), a message is sent across the communications bus to a central module that stores this fault for later reporting.

When your mechanic connects his laptop to the special diagnostic port on your car he is actually connecting that laptop directly to the communications bus. Once connected to the bus he can monitor the same data that is sent to any part of the car, including the dashboard and more importantly the fault logging module.

By reading this fault log he is then able to immediately understand historic faults of the car and view electronic warnings of minor issues you might not have picked up on. In essence, the fault log is like your car’s very own black box!

We hope that this two part series has given you a brief understanding of the ECU and the functions it performs. Check back next week when Tech-Talk! will be outing more of the many mysteries technology holds in your everyday motoring life!