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Nomenclature: ECM is to PCM as MIL is to CEL

  • Posted: 12-21-2015 07:01 PM
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The modern automobile's engine is controlled by a computer. While many engineers and mechanics will simply refer to the computer just that, a "computer," others will call it a "controller" or a "control unit."

The factory engineers will generally have a more specific term for the controller though. While there are numerous computers, controllers, and other electronic modules in the car, the ones related to engine operation are commonly referred to as one of the following:

  • "ECM" = Engine Control Module
  • "ECU" = Engine Control Unit
  • "PCM" = Powertrain Control Module (usually reserved for cars with automatic transmissions, as this unit will assist control over the transmission as well)

Also commonly tossed around terms are related to "engine lights." This is the little lamp that can come on the meter panel if the car's ECM/ECU/PCM detects and issue with the engine.

  • "MIL" = Malfunction Indicator Lamp
  • "CEL" = Check Engine Light

These lights are asking for the car's computer to be checked out for a problem. The light is triggered by a "code" in the computer which let's a technician know where to start investigating the problem. Some people also call them "idiot lights" but we won't be talking about them here.

Lastly, many cars come with "Maintenance" lights. The car's odometer works with a log of your driving habits to determine when it is time to perform routine maintenance. These don't indicate a problem with the car like a "Check Engine" light would, so don't get freaked out when the dashboard asks for maintenance.

Know of any more we forgot? Drop a comments and we'll add it!



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