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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  1. Great information..

  2. 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

    1. 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

    2. 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

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

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

  5. 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.

  6. 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.

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

    1. That is normal if the jumper cables were on the other car it was running energy already through them most times they will touch them to see if they are working so that usually makes sparks so no there is no problem with your car

  8. 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??

  9. Hey, Thanks for sharing articles your article is very interesting and very informative. I am sharing your article in my social media accounts. If you are interesting to know Car ECM repairing training course online. And how you can became a master in Engine Control Module Expert within 30 days. Then visit us our official websites and join our courses at affordable price.

  10. My 2004 BMW 545i won’t light up clustered or program scream seat’s windows power lockdown ignition don’t Crank position sensors are replaced.what can it be?

  11. […] The fuel pump is usually controlled by a relay which is, in turn, controlled by the ignition switch. However, the relays can also be controlled by ECM in certain cars. […]

  12. did any of you just have your died die on you in the middle of the road with no real warning?? trying to make sure this is what it the problem. thanks you

  13. […] The fuel pump is usually controlled by a relay which is, in turn, controlled by the ignition switch. However, the relays can also be controlled by ECM in certain cars. […]

  14. […] a truck, the ECM controls most of the engine operation. A faulty diode can cause a variety of different problems. One of […]

  15. I have a Chevy Tahoe. I used it the other day to jump off another vehicle of mine. The other vehicle has 2 batteries. I hooked up my Tahoe on one battery, charger on the other one. When I went to start the other vehicle, my Tahoe died. Long story short….every time I open my door, or turn lights on, a/c…..Tahoe dies. It’s not the alternator (13.99 steady volts). Does anyone out there know what this could be? ECM? I’m definitely confused!

  16. I have a question if anyone might be able to help I’d really Appreciate it..So I have a 2008 Mercedes ml350 that was in someone else’s possession and then the car wouldn’t start when I went to pick it up and that person told me that they were spraying something down and I guess they got water in the ecu and fried the ecu and they said that when that happened it caused all the other computers in the car to get fried as well and since that person is not a mechanic I was wondering if anyone on here would be able to tell me if that sounds plausible or if it would have just been the ecu that got fried? And if so then how many computers does an 08 ml350 have? And what would be my best course of action from this point?

    1. It’s very possible that the ECM was damaged when being sprayed with water, but your best bet would be to get a FIXD sensor to find out for sure. Even if your Mercedes won’t start, you can still plug the sensor in to see what trouble codes are present. If the ECM was damaged, it will need to be replaced. Modern vehicles have dozens of computers, although it isn’t likely that others were damaged due to the ECM being sprayed.

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