Description of On-Board Diagnostics

Fig. 4 ECCS System:

Fig. 2 Electronic Concentrated Control System (ECCS):

The Electronic Concentrated Control System (ECCS), Figs. 2, incorporates the fuel injection system and employs a micro-computer within the control unit. The micro-computer processes incoming signal data from engine and vehicle sensors and computes signal combinations to be sent to the electrical actuators.

The ECCS/ECU control unit determines basic injection by input signals from both the crank angle sensor and air flow meter. The mixture ratio feedback system is used for precise control of mixture ratio to the stoichiometric point at which the three-way catalytic converter most efficiently controls CO, HC and NOx emission simultaneously. This system uses an exhaust gas sensor in the exhaust manifold to check air fuel ratio. The control unit adjusts the injection pulse width according to sensor voltage so mixture ratio will be within range of the stoichiometric air fuel ratio. This stage refers to the closed loop control condition. The open loop control condition refers to that under which the ECU detects any of the following conditions and feedback control stops in order to maintain stabilized fuel combustion.
1. Deceleration.
2. High load, high speed operation.
3. Engine Idle.
4. Malfunction of exhaust gas sensor or its circuit.
5. Insufficient activation of exhaust gas sensor at low engine temperature.
6. Engine starting.

The mixture ratio feedback control system monitors the mixture ratio signal transmitted from the exhaust gas sensor. This feedback signal is then sent to the ECU to control the amount of fuel injection to provide a basic mixture ratio as close to the theoretical mixture ratio as possible. However, the basic mixture ratio is not necessary controlled as originally designed. The difference between the basic and theoretical mixture ratios is monitored in this system. This is computed in terms of fuel injection duration to automatically compensate for the difference between the two ratios.