Equus 3120 - OBD 2&1 Tool Kit - Manual (Page 49)

OBD2 & 1 47
E
Ford OBD1 Systems
DIAGNOSTIC TROUBLE CODES / CODE RETRIEVAL PROCEDURES - OVERVIEW
DIAGNOSTIC TROUBLE CODES (DTCs)
Diagnostic Trouble Codes, or Fault Codes, can be used to identify
engine systems or components that are malfunctioning. The computer
records codes for two types of problems:
■ "Hard" Diagnostic Trouble Codes
"Hard" DTCs represent problems which are happening now and
cause the instrument panel Malfunction Indicator Lamp (MIL) or
Check engine light to illuminate and remain on until the failure is
repaired. A DTC is stored in the vehicle's computer memory for
each fault detected. A Tool or Scanner can be used to retrieve
DTCs that are stored in the vehicle's computer memory.
■ Intermittent/History DTCs
Intermittent/History DTCs are stored in the computer's memory for
problems that occur intermittently, or for problems that happened in
the past but are not currently present. Intermittent DTCs may cause
the Malfunction Indicator light to flicker or stay on until the intermit-
tent malfunction goes away. However, the corresponding fault code
will be stored in memory as a history DTC. If the malfunction that
caused the history DTC to set does not recur within a predeter-
mined length of time (usually within 40-80 ignition key start cycles),
the computer will automatically erase the related fault code from its
memory.
CODE RETRIEVAL PROCEDURES
Overview of Ford Code Retrieval Process
Ford's computer self-diagnostic system is divided into four main sec-
tions:
1. "Key On Engine Off" (KOEO) Self-Test
2. "Continuous Memory" (CM) Self-Test
3. "Key On Engine Running" (KOER) Self-Test
4. Other EEC-IV System tests
These Self-Tests are specially designed to monitor and/or test the var-
ious components and circuits that are controlled by the vehicle's com-
puter, and to save and/or transmit diagnostic test results to the Tool in
the form of numerical fault codes.
The "Continuous Memory" Self-Test is designed to run continuously
whenever the vehicle is normal operation. If a fault is detected by the
"Continuous Memory" Self-Test, a fault code is saved in the vehicle's
computer memory for later retrieval.
Ford’s On-Board Diagnostic Self-Tests are designed in such a way that
in order to properly diagnose a problem, you
must perform all the Self-
Tests, in the proper sequence.