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INTRODUCTION
HOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS
01 -- 25
COROLLA Supplement (RM1129E)
SYMPT OM CONFIRMATION AND DIAGNOSTIC TROUBLE CODE
HINT:
The diagnostic system in the COROLLA has various functions.
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The first function is the Diagnostic Trouble Code (DTC) check. A DTC is a code stored in the ECU
memory whenever a malfunction in the signal circuits to the ECU occurs. In a DTC check, a previous
malfunction’ s DTC can be checked by a technician during troubleshooting.
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Another function is the Input Signal Check, which checks if the signals from various switches are sent
to the ECU correctly.
By using these functions, the problem areas can be narrowed down and troubleshooting is more effec -
tive. Diagnostic functions are incorporated in the following systems in the COROLLA:
System
DTC Check
Input Signal Check
(Sensor Check)
Diagnostic Test
Mode (Active Test)
ECD System [IND -- TV]
(with Check Mode)
Multi -- mode Manual Transmission System
Engine Immobilizer System
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In the DTC check, it is very important to determine whether the problem indicated by the DTC is: 1)
still occurring, or 2) occurred in the past but has since returned to normal. In addition, the DTC should
be compared to the problem symptom to see if they are related. For this reason, DTCs should be
checked before and after c onfirmation of symptoms (i.e., whether or not problem symptoms exist) to
determine current system conditions, as shown in the flowchart below.
Never skip the DTC check. Failing to check DTCs may, depending on the case, result in unnecessary
troubleshooting for systems operating normally or lead to repairs not pertinent to the problem. Follow
the procedures listed in the flowchart in the correct order.
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A flowchart showing how to proceed with troubleshooting using the DTC check is shown below. Direc -
tions from the flowchart will indicate how to proceed either to DTC troubleshooting or to the trouble-
shooting of each problem symptom.
1
DTC CHECK
NEXT
2
MAKE A NOTE OF DTCS DISPLAYED AND THEN CLEAR MEMORY
NEXT
3
SYMPTOM CONFIRMATION
Result:
Result
Proceed to
Symptoms exist
A
No symptoms exist
B
A
B
4
SIMULATION TEST USING SYMPTOM SIMULATION METHODS
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TOYOTA COROLLA REPAIR MANUAL SUPP 1129E