The ECU, or engine control unit, is part of your car’s computerized brain and is responsible for monitoring and managing all aspects of engine operation. For anyone who isn’t interested in upgrading their car for higher performance, the stock ECU is all that will be needed. However, if you’re contemplating building a high-performance machine, you’ll need a reprogrammable ECU that can be flashed to change your engine’s performance.

Stock ECUs

Your car comes with an unalterable ECU (with some very minor exceptions). It runs on software that can sometimes be upgraded, but only to a better version of the automaker’s software, and then only rarely. Sometimes you can “tweak” stock settings, but that’s also limited. These come preset from the factory for your car’s engine as it was when it was built. If you’ve made modifications to the engine designed to boost power, there’s a chance that the stock ECU won’t cut it. Most ECUs are not programmable/reprogrammable. However, there are aftermarket options that can be reprogrammed.

Aftermarket reprogrammable ECUs

Aftermarket programmable ECUs replace your stock computer with an aftermarket computer. These are designed to let you adjust pretty much any setting you want for the engine, from ignition control to controlling intercoolers and more.

Making adjustments to a reprogrammable ECU is generally simple – you connect the ECU to a computer loaded with the right software. The engine controls and settings are displayed through this software, and they can be adjusted with a mouse or a keyboard. However, it’s vital that only a thoroughly trained professional adjust your engine settings. If you’re not entirely sure what you’re doing, it can be very easy to throw off the entire engine.

Do you need a reprogrammable ECU?

Chances are good that you don’t need a reprogrammable ECU unless you’re doing serious modifications to your car’s engine for better power and performance. In this instance, even programmable stock ECUs won’t offer the unlimited access to systems and settings needed to achieve the level of performance you want.

This article originally appeared on YourMechanic.com as What Is a Reprogrammable ECU? and was authored by Valerie Johnston.


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