Equus 3120 - OBD 2&1 Tool Kit - Manual (Page 80)

78 OBD2 & 1
E
Servicing DTCs
SERVICING DTCs - OBD I
Never replace a part based only on the DTC definition.
Each DTC has a set of testing procedures, instructions and
flow charts that must be followed to confirm the location of
the problem. This information is found in the vehicle's service
manual. Always refer to the vehicle's service manual for
detailed testing instructions.
1. Determine engine system(s) condition by viewing the Tool's LCD
display for any retrieved Diagnostic Trouble Codes, code definitions
and interpreting the green, yellow and red LEDs.
The green, yellow and red LEDs are used (with the LCD dis-
play) as visual aids to make it easier to determine engine sys-
tem conditions.
2. Green LED - Indicates that all engine
systems are "OK" and operating nor-
mally. No trouble codes are present. If
you are not experiencing any vehicle
problems NO FURTHER TESTING IS
REQUIRED.
■ If you are still experiencing vehicle
problems even through the green
LED illuminates, the problem is not in
the computer control systems. See the NO CODES trou-
bleshooting section of your vehicle's repair manual for further
troubleshooting instructions.
3. Yellow LED - Indicates an Intermittent or History DTC is present.
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 intermittent mal-
function 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 predetermined length of time
(usually within 40-80 ignitio key start cycles), the computer will auto-
matically erase the related fault code from its memory.
Retrieving and using Diagnostic Trouble Codes (DTCs)
for troubleshooting vehicle operation is only one part
of an overall diagnostic strategy.