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Similaire à Diagnosis.pptx (20)
Diagnosis.pptx
- 2. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
DIAGNOSIS
• ECU has a self diagnostic system which constantly monitors the
input signal (voltage).
• Compares them to the standard values and determines any
abnormality
• ECU illuminates the MIL (Malfunction Indicator Light) and
stores a DTC (Diagnostic Trouble Code) in its memory.
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EXAMPLE FOR WATER
TEMPERATURE SENSOR
0.1v-4.8v normal
Less than 0.1v short
More than 4.8v open
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HAND-HELD TESTER
• It is also called intelligent tester, OBD-I/II, or scan tool.
• It displays DTCs by communicating directly with ECU
• Clear the DTCs from the ECU's memory
• Displays other information data , or serving as a voltmeter or
an oscilloscope.
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DIAGNOSIS...
• Depending on the vehicle model, the diagnostic system has;
• Normal mode: malfunction is registered in keep alive memory.
• Test mode: detects intermittent problems such as poor contact
which are difficult to detect in the normal mode.
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FAULT DETECTION
PRINCIPLES
• ECU is programmed:
• to accept sensor signal values within a certain range to be
normal, and
• signals outside of that range to be abnormal
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LOCATION OF CHECK CONNECTOR
AND TOYOTA/TOTAL DIAGNOSTIC
COMMUNICATION (TDCL)
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RETRIEVING TROUBLE
CODES
1. Using check engine lamp
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CHECK ENGINE LAMP
• lamp should come on when the ignition switch is turned on
(engine not running).
• lamp should go off. If the light remains on, it indicates that the
diagnostic system has detected a malfunction or abnormality in
the system.
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Electrical circuitry of check engine lamp
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RETRIEVING TROUBLE...
2. Using scan tool (OBD I, II)
• 1996 or newer cars are OBD II compliant (or
European OBD, EOBD, or Japan OBD, JODB),
and are provided with16 pin connector, called a
J1962 connector.
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RETRIEVING TROUBLE...
3. Using computers with diagnostic software
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READING DIAGNOSTIC CODES
USING CHECK ENGINE LAMP
Normal mode
• Initial conditions:
• Battery voltage at 11v or higher
• Transmission in “N” range
• All accessories switched off
• Switch on ignition key
• With special cable connect terminal T or TE1 with
terminal E1 on check connector or TDCL.
• Read the diagnostic code by the number of flashes of the
check engine lamp.
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DIAGNOSTIC CODES
One digit code
Normal code
Malfunction code
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DIAGNOSTIC CODES
Two digit code
Normal code Malfunction code
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CLEARING DIAGNOSTIC
CODES
• After the diagnostic code check, remove the special cable from
the check connector
• Repair the fault and clear the diagnostic code by removing
BATT 15A fuse or battery terminal for 10 seconds.
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• If faulty signal is detected, ECU uses data stored in memory
to continue engine operation or stops the engine
• Example, IGF…….no injection, MAP/VS/KS….standard data,
KNK…maximum retard, etc
Fail-safe function
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BACK-UP FUNCTION
• If trouble occurs with the microprocessor inside ECU, it
switches to back-up IC for fixed signal control.
• Back-up IC uses programmed data of
• Ignition timing
• Injection duration
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RETRIEVING TROUBLE
CODES
1. Using an analogue voltmeter connected to VF terminal of EFI
service connector
