Engine Control Module: Description and Operation

Fig. 14 ECU Inputs And Outputs (Carb):

The Electronic Control Unit contains logic circuits that sense the inputs and apply outputs as required to control emissions and effect smooth engine operation. Some of the Control Unit functions are:

Air Injection Function:
This system makes use of vacuum pulses in the exhaust manifold to draw air from the air cleaner to the exhaust manifold to promote oxidation of hydrocarbons.

Back-up Functions:
1. Fail-Safe Function
When an abnormality occurs in the signal from a sensor, the control unit ignores that signal and assumes a preprogrammed value that allows the engine to continue to run.
2. Back-Up Function
When an abnormality occurs in the control unit itself, a back-up circuit independent of the system permits minimal driving.
3. Self-Diagnosis Function (Check Engine Warning light and LED indicator)
When an abnormality occurs in a signal from a sensor, the control unit lights the Check Engine warning light, stores the failure code in erasable memory and indicates the code with a LED on the control unit anytime the ignition is on. When the ignition is initially turned on, the control unit supplies ground for the Check Engine warning light for about 2 seconds.

Evaporative Function
The Evaporative Control System minimizes the amount of fuel vapor until it can be purged from the canister into the engine and burned.

EGR Function
The EGR System is designed to control of oxides of nitrogen emissions by recirculating a part of the exhaust gas into the intake manifold through the EGR valve mounted on the intake manifold.

Feedback function:
The Air-fuel mixture ratio feedback on this vehicle is performed using the oxygen sensor, the EACV and the control unit.

Fuel Cut-off:
The fuel cut-off relay applies voltage to the fuel pump whenever ignition pulses are applied to the fuel cut-off relay.

Idle Function:
Idle speed is controlled through the use of the EACV and the A/C idle boost system.