Toyota Sienna Service Manual: Symptom confirmation and diagnostic trouble code
HINT:
The diagnostic system in the SIENNA has various
functions.
- 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.
- 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 effective.
Diagnostic functions are incorporated in the following
system in the SIENNA.


- In the DTC check, it is very important to determine
whether the problem indicated by the DTC either: 1)
still occurs, or 2) occurred in the past but has 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
confirmation 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 related to the problem. Follow the
procedures listed in the flowchart in the correct order.
- The following flowchart shows how to proceed with
troubleshooting using the DTC check. Directions from
the flowchart will indicate how to proceed either to
DTC troubleshooting or to the troubleshooting of each
problem symptom.
- DTC CHECK

- MAKE A NOTE OF DTCS DISPLAYED AND THEN CLEAR MEMORY

- SYMPTOM CONFIRMATION
Result 


- SIMULATION TEST USING SYMPTOM SIMULATION METHODS

- DTC CHECK
Result 

- SYMPTOM CONFIRMATION
Result 
If a DTC was displayed in the initial DTC check, the
problem may have occurred in a wire harness or
connector in that circuit in the past. Check the wire
harness and connectors.


| TROUBLESHOOTING OF EACH PROBLEM SYMPTOM |
The problem still occurs in a place other than the diagnostic
circuit (the DTC displayed first is either for a past problem or
a secondary problem).
HINT:
In troubleshooting, confirm that the problem symptoms
have been accurately identified. Preconceptions should be
discarded in order to make an accurate judgment. To
clearly understand w ...
HINT:
The most difficult case in troubleshooting is when no
problem symptoms occur. In such a case, a thorough
problem analysis must be carried out. A simulation of the
same or similar conditions ...
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HINT:
Use the same procedures for the RH side and LH side.
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