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Tech - What does the ECU do?

What does a VW ECU do?

A lot. A whole lot. A Volkswagen ECU, like virtually all other modern car's ECU is a small computer that is constantly checking sensors, adjusting settings, and logging information.

A Volkswagen ECU is checking many sensors all at the same time. One of the things that the Volkswagen ECU is checking is all of the sensors and devices related to emissions control for cleaner exhaust. The Throttle Position Sensor knows how far open the throttle is, the Mass Air Flow sensor measures incoming air. The Oxygen Sensor measures the exhaust. There are Engine Speed sensors, Cam and Crank Position sensors, Cylinder Knock sensors, coolant temperature sensors, oil temp sensors and others. All of these sensors are check by the ECU to give the proper amount of fuel, air, and spark at the precise timing to make the car run smooth and clean.

The VW ECU reads data from these sensors to determine how much fuel the engine needs and when to ignite the fuel (ignition timing)

Each of these sensors has a default value - a specific voltage or resistance (ohms). If this value is incorrect, either too high or too low for the current situation, the Check Engine Light (CEL) will light up on your instrument cluster. There are literally hundreds of error codes that the ECU can store. If they are critical to the emissions system of safety of the engine, the CEL will come on.

Now you might wonder...If the VW ECU has this much control over the engine, can it be modified to make the engine perform better rather than run cleaner?

Yes. Yes indeed. That is where performance ECU re-mapping comes in. A skilled programmer can dissect the inputs and outputs of the stock ECU and re program or insert a new chip with a slightly modified program that will alter the expectations of the ECU, or change the fuel delivery and ignition timing. I won't go into details here, thats for another article.