What is an Engine Control Module (ECM)?

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 most everything required to operate newer cars go through the ECM, if not directly controlled by it.

Diagram of a car

When does the ECM need to be replaced?*

  • Check Engine Light is illuminated
  • 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. 

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.

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Comments 9

Alfredo Torres

December 18, 2018

Great information..


July 9, 2019

I have an 88 Ford Econoline 150 van it keeps idling High and acts like it wants to stall more at lower speeds and when stopped it seems I had it stall wants and could not get it started had it towed replace the ignition modulator it was running good for a few days then it went back to the high idle and acting like it wants to stall very frustrating I cannot figure out the problem also when it acts like it’s going to stall it does it quickly like it doesn’t slowly glug down it just acts like cut off quickly then picks back up please any advice would help


December 9, 2019

Hi Jessica, I have the same problem on a corsa gamma 2006,did you by any chance find a solution for this? I need help, all these mechanics do not know what is wrong

kitandwe shafic

May 3, 2020

They have to use a scanner and a scope to monitor the oxygen sensor signal and the throttle position sensor ,either change oxygen sensor or clean the tps and flap

Bucklin Moon

August 6, 2019

HUGE surprise to have a complicated engine part explained clearly and succinctly. Thank you.


August 25, 2019

Uh, Jessica, we’ve had a problem, ECM… I’m now more thoroughly educated now

jacqueline ganus

November 1, 2019

Hi I have a 2007 Kia Rondo I bought it two Friday’s ago and has not been able to drive it since because the check engine light came on and no one can tell me why? I’ve tried to locate the E O M. because the engine will not speak to the mechanics scanner to tell whats wrong.

Ava Johonson

December 21, 2019

The car engine control unit had the software installed in it that controls the whole mechanism of the car. To improve the performance of the car, the experts now have to re-write the settings of the software installed in ECU. By having tuning, you can have a lot of benefits. Here is the complete information on ECU tuning – Hs-tronic.


January 4, 2020

I have a jeep Cherokee 2016 and somebody put the jumping cables on wrong and I saw sparks what is wrong with it


October 4, 2020

Hi, pls I have a Toyota Corolla LE 1998 which I actually bought as used car recently but I lately discovered it starts emitting Black smoke. The injectors have been servived but still persists. We just discovered the oxygen sensor has been disconnected! Could that be the cause pls??

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