GM 3123 Manuel Du Propriétaire page 14

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NOTE:
If "Service Engine Soon" light does not turn on, the initial
stored fault codes were all "intermittent" fault codes.
(Refer to the "Diagnostic Procedures" section in the
manufacturer's service manual for your vehicle.)
8.
Follow the testing and repair procedures outlined in the
manufacturer's service manual for your vehicle to correct
"hard" faults. Codes should be addressed and eliminated
in the order they were received, erasing and retesting
after each repair is made to be sure the fault was
eliminated. Code 12 will appear alone when no other fault
codes are present.
NOTE:
Whenever codes 51, 52, 54, or 55 are displayed with
other codes, troubleshoot and eliminate the "50
Series" codes first, then proceed with the lower-
numbered codes.
9.
Turn off ignition and remove the Code Reader.
2.3.1 Servicing Fault Codes
Diagnostic trouble codes indicate a problem in a circuit, not
necessarily a faulty component. DO NOT replace components
based only on trouble codes without first following the service
procedures described in your vehicle's repair manual. Most
faults (including those that set trouble codes) are caused by
damaged, shorted or open wiring, damaged or corroded
connections, improper voltages or grounds, or other
mechanical problems.
Sometimes a fault in one circuit or system will cause the
computer to set a fault code for a different circuit or system.
Example:
A defective spark plug wire can cause a "rich condition" fault
code to be set on the oxygen sensor circuit. In this case,
replacing any component in the oxygen sensor circuit will not
correct the fault, because the problem is caused by the
defective spark plug wire and not by the oxygen sensor circuit.
This is called a "false" code.
For this reason, it is IMPORTANT that you make a thorough
inspection of all systems: wiring, hoses, vacuum, engine
mechanical, charging, ignition, power, ground, fuel, (some of
these systems are not connected to the computer system, but
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It may be necessary to test drive the vehicle to
reset "hard" fault codes 13, 15, 24, 44, 45, and 55
after they have been erased.
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