Reprogramming Engine Control Modules 101

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Reprogramming Engine Control Modules

Does your “check engine” light stay on even though the fuel cap is tight? Does your gas mileage get just a bit worse year after year? How about that engine noise? Does it sound rougher than normal, even though you keep your oil changed?

If any of this sounds familiar, you may need your ECM reprogrammed. Simply getting your ECM reprogrammed can fix many of the problems that once required hours of careful troubleshooting and hands-on repairs.

What Does an Engine Control Module (ECM) Do?

Your engine not only drives your car, but provides power to every other vehicle subsystem. The ECM is the brains behind your car’s brawn. It’s the on-board computer that controls literally everything your engine does. Here are just a few of the important things your ECM does:

Optimizes the Air to Fuel Ratio: The ECM constantly measures the mixture of air and fuel inside the piston cylinders during combustion. It automatically injects enough fuel to produce the optimum ratio of air to fuel. When the optimum ratio is reached, complete combustion occurs and the engine creates maximum power.

Corrects Ignition Timing: For the engine to create maximum power, the spark plugs must fire at just the right moment. However, sometimes spark plug timing can be a little off. The ECM automatically corrects that. When combustion occurs at just the right moment, your pistons work the hardest—and only then will your engine produce the most horsepower!

Controls Engine Idle Speed: Less engine power is needed while your car idles. The ECM automatically reduces the engine’s power output by decreasing the amount of fuel injected. You end up wasting less fuel and less money.

Why Should I Reprogram My ECM?

Your engine takes a beating. It’s built to last, but after a while, it just doesn’t work like the day your car rolled off the assembly line. Parts become worn from friction and don’t fit quite as tightly. Constant vibration loosens engine parts just enough to affect performance. Your parts may not be bad enough to warrant replacement, but the ECM should be reprogrammed to compensate for their older, more road-worn condition. With optimal ECM programming, your engine will run much more efficiently.

ECM reprogramming is also a trick high-performance gear-heads use to maximize engine power output. Reprogramming can improve spark plug timing and fuel enrichment—and can help boost pressure on turbocharged engines to squeeze out every last drop of horsepower.

Reprogramming your ECM is necessary for keeping your vehicle control software up to date. Much like the operating system on your home computer, improvements in software are often made by your car’s manufacturer. The software can be updated simply by downloading and installing the latest version.

How Do I Reprogram an ECM?

It’s not like changing the oil in your garage — it requires expensive, professional tools.  With these tools the whole process is fairly simple and it’s almost entirely automated. No parts need be removed. You don’t even need any tools. All the technician has to do is make sure everything is connected properly.

A diagnostic scanner is attached to your car’s OBD II port, usually located under the steering wheel. The old programming is erased, then replaced with the latest software provided by the manufacturer. The whole process should take only about fifteen minutes. If the new software fails to transfer, the process is restarted. If it fails multiple times, it’s likely the result of a bad connection and can be easily diagnosed and fixed.

Many repair shops will tell you reprogramming should be done every few years—and maybe they’re right. However, it’s usually only something that needs to be done if you’re experiencing any of the problems we discussed earlier. Unless a recall or mandatory update is issued by the manufacturer, it isn’t something you should treat as routine as it’s rarely, if ever, part of your car’s maintenance schedule.

One thing ECM reprogramming can’t do is fix mechanical problems where parts need to be replaced or cleaned. Things like vacuum leaks, dirty fuel injectors, burned-out spark plugs, and worn piston rings definitely need hands-on attention. is one of the leading online retailers of engine control modules on the web.  We can either repair your current ECM or send you one freshly programmed and plug and play — you can get it and install it in just a few minutes.