But quite often they mean the module that controls the engine. In many cases persons that has spoken to me about "the" ECU/ECM don't really know what they were talking about. And they are very seldom interchangeable. One ECU can not be said to be better than another (except maybe some quality issues), they just have different domains that they handle in. Cars of today often have even more ECU's and larger bus networks. Often with a bus system (for example CAN, LIN, K-Line, Flexray, MOST etc). Most of the ECU's are connected with one or more of the other ECU's. For example my -97 Range Rover has several ECU's: ECM (Engine Control Module), BeCM (Body electronic Control Module), ABS (for the brakes), Transmission, EAS and some more. The term ECU is often used for Electronic Control Unit (which could be more or less any electronic unit in the car). Different brands has different names for the same stuff, and also same name for different stuff, which can get a little confusing. The term ECM could (just as says) be used for both Electronic Control Module or Engine Control Module. I could go on and on, but this is just my personal experience with those terms. I guess what it boils down to honestly is what the engineers say it is. Which could literally mean anything driven by a computer. I have a few friends that are electrical engineers and they use the term ECM for "Electronic control module". ECM is generally a "catch All" term that can mean quite a few things. I see that PCM and ECU are the two most used terms for the actual engine computers. Maybe even power steering and emissions as well. It perhaps could be that it controls the transmission and engine. If your manufacturer uses the term PCM, it will most likely control multiple aspects of your "Powertrain". You would probably have additional computers for things like windows, air conditioning, transmission and they all have their names as well. If you think about it from the engineers standpoint they can mean different things though.Įngine Control Module would most likely be your control unit dedicated to all electronics/ Sensors dedicated to your engine only. I usually see ECU when referring to Asian vehicle companies. ECM, PCM, and ECU are generally manufacturer specific. My shop specializes in computer systems on some of the newer vehicles (Mostly Japanese), but we do work on anything given the chance. From my personal experience with this particular subject you have many variables that come into play.