General System Description

Fig. 17 ECCS System:

The term used by Nissan to identify the computerized engine control system is ECCS (electronic concentrated engine control system). This system is comprised of an ECU (electronic control unit) or central processor, several sensors or input devices and actuators or output devices. All components and circuits must work in conjunction with each other for the system to control emissions and maintain fuel economy and performance at optimum levels.
In addition the system has three other features:

1. SELF-DIAGNOSTICS
The ECU monitors several circuit and components to determine if they are functioning properly. If a malfunction is detected in certain circuits the "CHECK ENGINE" lamp (California only) will be illuminated to alert the driver that a problem is occuring. The lamp will remain illuminated as long the fault is present. The ECU will store a code in its memory to aid the technician in diagnosis. If the lamp turns off, the fault is no longer present, but the code will be stored for 50 attempted engine starts or until the code is cleared from the memory. This aids in diagnosing intermittant problems.

2. FAIL-SAFE OPERATION
The ECU will substitute an input signal in the event of a failure in the air flow meter, engine temperature sensor or throttle sensor circuits. The engine will operate at reduced capacity to allow the vehicle to be driven until repairs can be made.
The "CHECK ENGINE" will blink when the ECCS system is in the fail-safe mode.

3. MIXTURE RATIO SELF LEARNING
The ECU monitors O2 sensor voltage and will regulate injector duration to provide a basic mixture ratio as close to the theoretical mixture as possible. Manufacturing differences and changing operating conditions (engine wear, injector flow, etc.) will affect the the mixture ratio.
The difference between the basic and theoretical mixture ratios is quantitatively monitored and computed in terms of "Fuel Injection Duration" to automatically compensate for differences in the two ratios. This allows the system to compensate at a faster rate than if it had to rely only on a pre-programmed ratio.