How to reprogram your engine computer

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The under-dash engine diagnostic port of a 1999 Audi. This location for the diagnostic port is common for most modern vehicles.

Locate your vehicle's diagnostic port. The plug-in port is typically under the dash. (Photo Credit: CC BY/Scott/Vag-Com Scanning)

Flashing — or erasing and reprogramming — your engine’s computer is a legitimate way to keep a car’s engine control modules (ECMs) up to date. This is done on nearly all vehicles 1996 and newer to ensure that the microprocessors in such areas as the power train and fuel injectors are regulating their systems properly. If the programming is optimized, your car’s engine tends to run much more efficiently. It’s a bountiful cash crop for repair shops, who tend to charge between $80 and $120 for the service, according to Underhood Service. However, you can flash your car engine yourself – with the right tools.

How reprogramming an engine computer works

When reprogramming an engine computer, a scanner is attached to the diagnostic port in a car, which is typically inside the car, beneath the steering wheel. Old programming is erased, then replaced with the most up-to-date software provided by the auto manufacturer. It used to be that it was necessary to remove parts in order to complete the reprogramming process, but now all that’s necessary is a computer with an Internet connection, a USB cable and a scanning device that can connect with a car’s diagnostic port. The ECM is flashed with the new software direct from the manufacturer’s website.

How often does the ECM need to be flashed?

Auto repair shops say flashing should be done once every few years, and this may be appropriate. However, it’s typically only something that needs to be addressed on a need-to basis, unless a sweeping pronouncement is issued by the manufacturer as part of a recall movement. It definitely isn’t something a car owner should pay for as part of routine vehicle maintenance.

What a DIY flasher would need to do the job

It can be quite simple. Consult with your vehicle manufacturer’s website for software updates. Download the update into a flash programming device. Additional software for proper engine tuning may be necessary. Consult sources such as for more specific information. You should also consult with your state’s motor vehicle authority, as more radical aspects of engine programming may not be street legal, which is the case in tough emissions states like California.

New cars with fresh ECM programming start with auto loans



Underhood Service

Scotty Kilmer on reprogramming your car’s computer

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