General System Description

GENERAL DESCRIPTION
The information in Computers and Control Systems applies to engines which have a fuel injector mounted above a throttle body assembly. The entire assembly is mounted to the intake manifold and is referred to as Throttle Body Fuel Injection (TBI) unit.

These engines have controls which reduce exhaust emissions, and maintain good driveability and fuel economy.

Powertrain Control System
An Engine Control Module (ECM) is the heart of the control system. A network of sensors provide the ECM with information about engine operation and the various systems it controls. Details of the basic operation, diagnosis, functional checks and on-vehicle service procedures are covered in Computers and Control Systems.

Fault Detection
The ECM has the ability to do some diagnosis of itself, as well as other parts of the system. When the ECM detects a malfunction, it lights the Malfunction Indicator Lamp (MIL) in the instrument cluster. At the same time a Diagnostic Trouble Code (DTC) is stored in the ECM's memory. The MIL does not indicate that the engine should be stopped right away, but that the vehicle should be checked as soon as reasonably possible.