What is the ECM and how does it work?
The Engine Control Module (ECM), also called the Engine Control Unit (ECU), ensures that your vehicle operates at optimal performance. The ECM monitors most of the sensors in the engine bay in order to manage your vehicle’s air-fuel mixture and regulate the emission control systems.
The ECM regulates four main parts of your vehicle’s operating systems: air-fuel ratio, idle speed, variable valve timing, and ignition timing. In terms of the air-fuel ratio, the ECM uses sensors to regulate the oxygen to fuel ratio detected in your car’s exhaust to detect an engine rich/lean reading. Some of these sensors include the mass airflow sensor(s), the oxygen sensor(s), air-fuel sensor(s). For the idle speed, the ECM relies on sensors located by the crankshaft and camshaft(s) that track your vehicle’s RPM and engine load by monitoring the speed of rotation of the engine. (RPM=Revolutions Per Minute) The variable valve timing system controls when the valves are opened in the engine to either increase power or fuel economy.
Lastly, the ECM controls the ignition timing, this is the position at which the spark plug is fired within the combustion cycle. Precise control of this timing allows for more power and/or better fuel economy. The ECM also controls multiple other systems on top of these main tasks. It is often called the brain of the car, and rightfully so, because almost everything required to operate newer cars go through the ECM, if not directly controlled by it.
When does the ECM need to be replaced?*
- Check Engine Light is illuminated. We recommend reading this article on how to quickly diagnose your car’s check engine light.
- Engine misfires
- Lower engine performance
- Car fails to start
*Before replacing the ECM, extensive diagnostics should be conducted to determine it as the root cause. Read our complete OBD2 scanner guide to learn everything you need to know about OBD2, including how to use it to diagnose your vehicle.
How Much Does it Cost to Replace the Engine Control Module?
The replacement of an ECM is not a cheap fix and can range between $900-$1000.
At FIXD, our mission is to make car ownership as simple, easy, and affordable as possible. Our research team utilizes the latest automotive data and insights to create tools and resources that help drivers get peace of mind and save money over the life of their car.