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How does an ECU work?

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  • How does an ECU work?

    Hi all,

    I keep reading things about resetting the ECU by disconnecting the negative battery cable. What exactly is being reset? I know that the ECU has a lookup table for fuel based on the RPM. But does the computer also calculate what the right value is based on sensor input? And then when does it use the calculated versus the stored value?

    If I reset my ECU, will the car run poorly for awhile and then get better as time goes on?

    BP powered 91 Festiva L
    -FMS springs, GR2 struts, Toyo T1R 195/45/14 on Swift GT alloys
    -Trunk mounted gel battery
    -Suzuki Swift GT seats, Grant GT steering wheel, auto-locks
    -Blaupunkt Melbourne deck with Bluetooth, sealed single 12" sub

  • #2
    the ECU takes in information from the TPS, AFM temperature sensor and )2 sensor to determine fueling. It also logs any trouble codes, does sensor tests.

    Resetting it just cleares out it's active memory like Trouble codes and some minor adjustment info. Usually within 20-50km's it relearns everything and your car runs back normally once the computer checks all the sensor inpouts and adjusts accordingly to your motor.

    Sorry if it sounds a bit simplisitc but Trying to word it so it's easily understood without tech mumbo jumbo.



    • #3
      if you re-set the ECU (i.e., every time the battery is disconnected for >10min or so) make SURE that you let the car sit and idle for a few min first! i "re-set" my ecu and then just up and drove it basically. ran real crappy. Then a mecanic explained to me that if you let it idle for a while it is "learning" everything again.... you can here the idle drop up and down some during the 5 min or so you hafta let it idle.

      after that you can drive it normal and it should be back to running, mine was having problems idling and now it idles great!

      i dont' really know how the ECU itself works, but thats the lil bit of info i do have...

      the keeper of a wonderful lil car, Skeeter.

      Current cars:
      91L "Skeeter" 170k, Aspire brakes, G15, BP, Advancedynamics coil overs, etc. My first love.
      1990 Kawasaki Ninja 250 - my gas saver, 60+mpg - 40k
      2004 MotoGuzzi Breva - my "longer range" bike - 17k

      FOTY 2008 winner!