As the electronic brain of a closed loop system, the engine control unit receives data from a number of vehicle-mounted sensors. Such data pertains to (but is not limited to) engine speed, coolant temperature, exhaust gas oxygen content, manifold vacuum and throttle valve position. In response to these ongoing inputs, the ECU continually controls the operation of a series of solenoid valves in order to maintain optimal operating conditions. As an example of its many functions, the ECU determines the operating period of the Air/Fuel (A/F) solenoid and controls the air/fuel ratio.
WARNING
The ECU is a very sensitive and EXPENSIVE electronic component. NEVER disconnect
power from the ECU (or any computer module) with the ignition key turned ON,
as this could destroy the module. This warning includes disconnecting the battery
cables. If the cables are removed with the key turned ON, this will remove power
from the ECU and quite possibly destroy it.