Electronic Engine Control

Diagnostic Chart:

ENGINE CONTROL MODULE
All engines have an Engine Control Module (ECM) to control the fuel system. The ECM varies the air/ fuel ratio by controlling the fuel flow through the injectors.

In addition, the ECM controls the ignition timing, fuel pump, and various other systems.

It is important to review the component and wiring diagrams in this Section for specific components controlled by the ECM and what systems are non-ECM controlled.

Driveability
The driveability diagnosis procedures apply to various systems in the vehicle. The procedures assume that the vehicle is worked on properly at one time and the problem is due to time, wear, dirt or other causes. Start with System Diagnosis / Flow of Diagnosis. This will describe a systematic diagnostic procedure.

Any system disconnected during diagnosis should be reconnected. This includes wires, hoses, linkage, etc.

Fuel Control System
The ECM controls the air/fuel delivery to the combustion chamber by controlling the fuel flow through the injector(s).

Electric Fuel Pump (in-tank)
The in-tank fuel pump is controlled by the ECM. When ignition is turned on, the pump will run for 2 seconds, then stop unless the engine is cranking or running.

Evaporative Emission (EVAP) Control System
This system has a canister which stores fuel vapor from the fuel tank. The fuel vapor is removed from the canister and consumed in the normal combustion process when the engine is running.

Ignition Control (IC)
This system is controlled by the ECM which controls spark advance (timing).

Exhaust Gas Recirculation (EGR)
The exhaust gas recirculation system uses ECM controlled valve to feed a small amount of exhaust gas back into the intake manifold to control formation of NOx.

Air Conditioning (A/C) Clutch Control
The ECM may control the air conditioning clutch on the compressor to improve idle quality.

Positive Crankcase VentilatioN (PCV)
The PCV system passes crankcase vapors into the intake manifold. This system is not controlled by the ECM and is used on all engines.

Maintenance Schedule
Refer to the Maintenance Schedule in Mainenance for the maintenance service that should be performed to retain emission control performance.