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Toyota/Lexus OBD1 Systems<br />
DIAGNOSTIC TROUBLE CODES / CODE RETRIEVAL PROCEDURE<br />
If your instrument panel indicator lights do not come on when<br />
you turn on the ignition, please refer to your vehicle's service<br />
manual. You may have problems in the car's circuitry. It is<br />
recommended that you fix these problems before retrieving<br />
DTCs from your vehicle’s computer.<br />
DIAGNOSTIC TROUBLE CODES<br />
Diagnostic Trouble Codes, or Fault Codes, can be used to identify<br />
engine systems or components that are malfunctioning. The computer<br />
records codes for the following two types of engine problems:<br />
� "Hard" Diagnostic Trouble Codes<br />
"Hard" DTCs represent problems that are occurring now and cause<br />
the instrument panel Malfunction Indicator Lamp (MIL) or Check<br />
Engine light to illuminate and remain on until the failure is repaired.<br />
A DTC is stored in the vehicle's computer memory for each fault<br />
detected. A <strong>Tool</strong> or <strong>Scan</strong>ner can be used to retrieve DTCs that are<br />
stored in the vehicle's computer memory.<br />
� Intermittent/History DTCs<br />
Intermittent/History DTCs are stored in the computer's memory for<br />
problems that occur intermittently, or for problems that happened in<br />
the past but are not currently present. Intermittent DTCs may cause<br />
the Malfunction Indicator light to flicker or stay on until the<br />
intermittent malfunction goes away. However, the corresponding<br />
fault code will be stored in memory as a history DTC. If the<br />
malfunction that caused the history DTC to set does not recur within<br />
a predetermined length of time (usually within 40-80 ignition key<br />
start cycles), the computer will automatically erase the related fault<br />
code from its memory.<br />
CODE RETRIEVAL PROCEDURE<br />
Retrieving and using Diagnostic Trouble Codes (DTCs) for<br />
troubleshooting vehicle operation is only one part of an<br />
overall diagnostic strategy.<br />
Never replace a part based only on the DTC definition.<br />
Each DTC has a set of testing procedures, instructions<br />
and flow charts that must be followed to confirm the<br />
location of the problem. This information is found in the<br />
vehicle's service manual. Always refer to the vehicle's<br />
service manual for detailed testing instructions.<br />
Check your vehicle thoroughly before performing<br />
any test. See BEFORE YOU BEGIN on page 18<br />
for details.<br />
ALWAYS observe safety precautions whenever working on a<br />
vehicle. See Safety Precautions on page 3 for more information.<br />
CanOBD2&1 107
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