General System Description

Circuit Diagram:

System Chart:

OPERATION
The term used by Infiniti to identify the computerized engine control system is electronic concentrated engine control system (ECCS). This system is comprised of an ECCS Control Module (ECM) 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 other features:

1. SELF-DIAGNOSTICS
The ECCS control module (ECM) has an on-board diagnostic system, which detects engine system malfunctions related to sensors or actuators. The malfunction indicator lamp (MIL) on the instrument panel lights up when a malfunction is detected twice (two trip detection logic).
TWO TRIP DETECTION LOGIC
When a malfunction is detected for the first time, the malfunction (DTC and freeze frame data) is stored in the ECM memory. <1st trip> The malfunction indicator lamp will not light up at this stage.
If the same malfunction is detected again during next drive, this second detection causes the malfunction indicator lamp to light up. <2nd trip>.
The "trip" in the "Two Trip Detection Logic" means performing of the "DTC Detecting Condition". Only the following on-board diagnostic items will light up or blink the MIL even in the 1st trip.
^ "Misfire (Criterion which will damage three way catalyst) -
DTC: 65-71 (P0304-P0300)
^ "Three way catalyst function" - DTC: 72 (P0420)

2. FAIL-SAFE OPERATION
The ECM will substitute an input signal in the event of a failure in the air flow meter, engine temperature sensor or fuel temperature 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 mixture ratio feedback control system monitors the mixture ratio signal transmitted from the front heated oxygen sensor. This feedback signal is then sent to the ECM. The ECM controls the basic mixture ratio as close to the theoretical mixture ratio as possible. However, the basic mixture ratio is not necessarily controlled as originally designed. Both Manufacturing differences (i.e. mass air flow sensor hot wire) and characteristic changes during operation (i.e. injector clogging) directly affect mixture ratio.
Accordingly, the difference between the basic and theoretical mixture ratios is monitored in this system. This is then computed in terms of "injection pulse duration" to automatically compensate for the difference between the two ratios.
"Fuel trim" refers to the feedback compensation value compared against the basic injection duration. Fuel trim includes short-term fuel trim and long-term fuel trim.
"Short-term fuel trim" is the short-term fuel compensation used to maintain the mixture ratio at its theoretical value. The signal from the front heated oxygen sensor indicates whether the mixture ratio is RICH or LEAN compared to the theoretical value. The signal then triggers a reduction in fuel volume if the mixture ratio is rich, and an increase in fuel volume if it is lean.
"Long-term fuel trim" is overall fuel compensation carried out long-term to compensate for continual deviation of the short-term fuel trim from the central value. Such deviation will occur due to individual engine differences, wear over time and changes in the usage environment.