LIGHTING SYSTEM Taillight Circuit
DESCRIPTION
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This circuit is only for vehicles with the daytime running light system or with automatic light control system.
Tech Tips
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For vehicles with the daytime running light system or with automatic light control system, the exterior lights (headlights, taillights, front fog lights and rear fog light) are controlled by the main body ECU.
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For vehicles without the daytime running light system and without automatic light control system, the exterior lights (headlights, taillights, front fog lights, and rear fog light) are not controlled by the main body ECU, so perform troubleshooting according to the Problem Symptoms Table Click here.
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The main body ECU receives the light control switch TAIL signal to control the taillight relay.
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When the light control switch is in the AUTO position, the main body ECU receives the ambient light level signal from the automatic light control sensor to control the taillight relay.
Tech Tips
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When any of the lights do not illuminate, check the bulb or wire harness that is related to the bulb.
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When all of the lights that are related to the TAIL relay do not illuminate and the TAIL fuse is normal, perform the taillight relay Active Test and read the light control switch TAIL signal value in the Data List to determine if the malfunction exists on the switch side or the relay side.
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The taillight relay is installed in the instrument panel junction block, so unlike conventional relays, it can not be removed for inspection.
WIRING DIAGRAM
INSPECTION PROCEDURE
Note
Inspect the fuses and bulbs for circuits related to this system before performing the following inspection procedure.
PROCEDURE
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PERFORM ACTIVE TEST USING INTELLIGENT TESTER
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Connect the intelligent tester to the DLC3.
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Turn the ignition switch to ON.
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Turn the tester on.
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Enter the following menus: Body / Main Body / Active Test.
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According to the display on the tester, perform the Active Test.
Main Body Tester Display Test Part Control Range Diagnostic Note Taillight Relay Taillight relay ON or OFF - OK Taillight relay operates. (Taillights illuminate.)
NG 
READ VALUE USING INTELLIGENT TESTER Click here
OK 
PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE Click here
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READ VALUE USING INTELLIGENT TESTER
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Connect the intelligent tester to the DLC3.
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Turn the ignition switch to ON.
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Turn the tester on.
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Enter the following menus: Body / Main Body / Data List.
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According to the display on the tester, read the Data List.
Main Body Tester Display Measurement Item/Range Normal Condition Diagnostic Note Head Light SW (Tail) Light control switch TAIL signal
ON or OFF
ON: Light control switch in TAIL or HEAD
OFF: Light control switch in neither TAIL nor HEAD
- OK Normal conditions listed above are displayed.
NG 
PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE Click here
OK 
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CHECK HARNESS AND CONNECTOR (BATTERY - INSTRUMENT PANEL JUNCTION BLOCK)
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Text in Illustration *1 Front view of wire harness connector
(to Instrument Panel Junction Block)
Disconnect the 3A instrument panel junction block connector.
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Measure the voltage according to the value(s) in the table below.
Standard Voltage Tester Connection Condition Specified Condition 3A-1 - Body ground Always 11 to 14 V -
Reconnect the instrument panel junction block connector.
NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK
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REPLACE MAIN BODY ECU
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Temporarily replace the main body ECU with a new or normally functioning one Click here.
NEXT
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PERFORM ACTIVE TEST USING INTELLIGENT TESTER
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Connect the intelligent tester to the DLC3.
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Turn the ignition switch to ON.
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Turn the tester on.
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Enter the following menus: Body / Main Body / Active Test.
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According to the display on the tester, perform the Active Test.
Main Body Tester Display Test Part Control Range Diagnostic Note Taillight Relay Taillight relay ON or OFF - OK Taillight relay operates. (Taillights illuminate.)
NG
REPLACE INSTRUMENT PANEL JUNCTION BLOCK
OK
END (MAIN BODY ECU DEFECTIVE)
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