HICustomer

Ecu reset is as simple as disconnecting battery, 30 secs should do it, you have to run through a relearn procedure but its simply a matter of going for a drive.

OK, memory.

Short term memory does 2 things, makes small variations to the amount of fuel being injected and the amount of ignition advance you get.
These variations are purely dependent on current operating conditions.

ie, ambient air temp, altitude, type of fuel and so on. These changes are made on the fly as the parameters can change quite quickly. The info is mainly centered around the O2 sensor and knock sensor inputs.

Long term memory does use the short term trims (Fuel and timing changes), But more so if the same short term alterations are happeneing consistantly. For instance, altitude changes, temp changes (winter to summer), even condtion of the engine. These will alter fuel maps and timing maps to suit conditions over the long term. This info is stored in the computer memory and will stay there (along with fault codes) even when key is off. There is 1 power wire connected to ECU to keep this long term memory there.

Disconnect the battery and you lose that, so fault codes are erased (except history codes) and the ecu has to relearn any long term trims that have been made so it may run rough for a little time.

Hope this helps.