What is an ECU/ECM and what does it do?
Every modern vehicle has an ECM (Engine Control Module) or ECU (Engine Control Unit). These terms are interchangeable and refer to your engine’s computer brain.
The ECM’s job is to read input from all the various sensors in your engine and make adjustments to your fuel, air, and spark ratios to keep your vehicle running properly and passing emission laws. Back in my early days as a tech, it was explained to me in simple terms that I still remember to this day.
Imagine a tiny little wizard sitting inside of a box under the hood. His box is full of dials and telescopes that let him view all the different sensors, and adjust other parts in order to make your vehicle run properly. If he looks down one telescope and that sensor tells him he needs to add gas, he dials up some more gas. Another sensor shows him there is too much air, so he dials back the air. He continually looks down the telescopes and adjusts dials as needed the whole time your vehicle is on.
History
ECUs were initially put into mass market automobiles by Volkswagen in 1968, showing up in the VW Type 3, but all the other major manufacturers weren’t far behind. Into the 70s and 80s as emission laws increased, every manufacturer started adding basic ECUs to monitor the fuel/air ratio and make sure you weren’t vomiting smog everywhere. In the late 70s GM partnered with Motorola to manufacture ECUs for all their production vehicles by 1981. Chrysler soon joined as well, while Ford partnered with Intel for their ECU needs for a few years, until they started building their own in house.
Modern ECUs
In the mid, to late 2000s computer processors had come a long way from the basic controls capable in the 80s. Technicians can now update software to fix bugs or alter the engine controls for more performance. In 2009 Google used Intel processors to make the first self-driving car, which led to Tesla, Volvo, and Audi creating their own self-driving cars. Current vehicles have an ECU working alongside several other control units, such as the body control module (BCM), transmission control module (TCM), and even separate modules for the radio, steering, seats, and doors. Each of these runs an entire system to deliver the comfort and performance modern car customers demand.
While most repairs and reprograms of ECUs cannot be done at home, oftentimes as with a PC or cell phone, your car ECU needs to be turned off and back on. There isn’t much reason to do this if everything is operating properly, but you would be surprised how many odd things can happen in your vehicle that can be fixed by simply unplugging your battery cables for 10 minutes. This will allow the capacitors in all your different control modules to discharge and essentially reset your ECU.
Yes turning your car off and back on will fix a wild amount of electrical mishaps. Next time you have an odd or intermittent problem, give that a shot before you spend time or money trying to diagnose a larger issue.
As always, feel free to comment below, tweet me @BowTiedGreaseMonkey, or shoot me a DM on Twitter with any automotive questions you may have, or any suggestions for future articles you would like to see.