What’s the Difference Between a Car’s PCM and a TCU? Or an ECM?

ECM From a 1996 Chevy Beretta

It’s accurate in many ways to talk about the PCM as the “brain” of your vehicle. The powertrain control module collects important information about your car’s performance and tells your car how to function. In addition, just like a brain has different lobes that control different functions of the body, the PCM contains different computing modules that control different parts of your car.

Usually, your PCM will consist of two main components: the engine control unit and the transmission control unit. The engine control unit controls the driving force behind your car. Among the functions in its jurisdiction are the control of the air/fuel ratio, control of ignition timing, and control of idle speed.

The transmission control unit, as you might guess, controls your car’s automatic transmission. It gathers information on how fast your vehicle is going and uses that data to determine what gear your car should be in. There are a number of sensors that transmission control units use to gather this information about speed. These include wheel sensors, turbine speed sensors, and throttle position sensors. After the information has been gathered, most modern transmission control units use electronic solenoids to carry out the appropriate commands.

A third computer that is an increasingly common component of PCMs is the body control unit. As modern cars develop more and more advanced accessories contained within the body, more car manufacturers find it helpful to dedicate an entire computer module to controlling the body of the car. The BCU is especially common in newer Chrysler models.

Just like all the lobes of the brain work together to keep our bodies moving, the different control units within the PCM work together to keep your car performing at its best. Unlike with a brain, if one of the components of your ECM fails, it is easy to repair or replace it. Solo Auto Electronics is a Florida auto computer store and is happy to help you find the quality parts and repair you need to keep your car on the road; contact us with any questions about our products and services.