Equus 3145 - Digital Ford Code Reader (1981 - 1995) - Manual (Page 17)

About Diagnostic Systems
FORD COMPUTER SYSTEM OVERVIEW
Chapter 2 14
1994: Ford introduces the EEC-V system (OBD-II). This is a
highly sophisticated system that uses more special programs
to enhance the computer's capability to monitor, detect and
report failures, especially to the vehicle's emission system.
This system was introduced on a limited number of 1994 and
1995 vehicles. Starting in 1996, all Ford vehicles (cars and
light trucks) sold in the US are equipped with the EEC-V
system.
NOTE: The Ford Digital Code Reader is compatible only with
the MCU and the EEC-IV Computer Control systems. The
EEC-I, EEC-II, EEC-III and the EEC-V (OBD-II) systems
require specialized equipment to diagnose computer problems
and/or retrieve fault codes and are not compatible with the
Ford Digital Code Reader.
FORD COMPUTER SYSTEM OVERVIEW
Ford vehicle's computers are factory-programmed with special
Self-Testing instructions that are specially designed to detect
any failures in the various systems that the vehicle's computer
monitors and controls. The computer monitors the vehicle’s
sensors (oxygen sensors, coolant temperature sensors, mass
airflow sensors, EGR valve, MAP sensors, etc.) and actuators
(fuel injectors, EGR system, idle air control, cooling fan, canister
purge solenoid, spark advance, etc.) for proper operation. All of
these devices are connected to the vehicle's computer by wires.
The sensors communicate with the computer by sending
voltage signals (inputs) that correspond with the vehicle's
current operating condition. If the voltage that the computer
receives from a particular sensor does not agree with the
voltage value that is programmed in its memory for that
particular driving condition. A Diagnostic Trouble Code is
generated that pertains to that particular circuit or system.
Actuators receive commands from the computer in the form of
voltage signals to perform a certain functions or adjustment.
Example: The computer might command a fuel injector to
increase the amount of fuel injected into the engine. After
the computer commands the fuel injector to inject more fuel
in to the engine, it then monitors the voltage signal from
that injector to ensure that the injector has responded. If
t h e f u e l i n j e c t o r ' s v o l t a g e s i g n a l d o e s n o t c h a n g e , i t
indicates that the fuel injector is not responding to the
computer’s command. The computer then determines that
there is a problem in the injector or injector circuit, and
generates a code related that particular problem. This code
is sent to the Code Reader during the Self Test procedure.
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