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The ECU changes air/fuel ratio timing and other things, based on variables that it receives from many different sensors in and around the engine to exhaust. Stored codes are erased from memory by disconnecting power to the ecu for at least 30 seconds. Disconnecting the negative battery cable will clear the memory of the ecu, as well as other solid state equipment such as the radio. The ECU may also be cleared by pulling the appropriate fuse from the underhood fuse and relay box.


An engine control unit (ECU) is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running. It does this by reading values from multidimensional maps which contain values calculated by sensor devices monitoring the engine.

Before ECU's, fuel injection, ignition timing, and idle speed were directly controlled by mechanical and pneumatic sensors and actuators.

Working of ECU
* 1.1 Control of fuel injection
* 1.2 Control of ignition timing
* 1.3 Control of idle speed
* 1.4 Control of variable valve timing
* 1.5 Electronic valve control