LIGHTING SYSTEM PROBLEM SYMPTOMS TABLE

Note

If the main body ECU (multiplex network body ECU) is replaced, refer to the Service Bulletin.
As the door control battery is installed between the vehicle battery and main body ECU (multiplex network body ECU), first perform the inspections in On-Vehicle Inspection to confirm that there are no malfunctions in the power source circuit for the main body ECU (multiplex network body ECU) before performing this troubleshooting procedure.
When replacing the combination meter assembly, make sure to replace it with a new one.
After the headlight light control ECU sub-assembly LH (main) is replaced, vehicle information registration and initialization are necessary.

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Tech Tips

Use the table below to help determine the cause of problem symptoms. If multiple suspected areas are listed, the potential causes of the symptoms are listed in order of probability in the "Suspected Area" column of the table. Check each symptom by checking the suspected areas in the order they are listed. Replace parts as necessary.
Inspect the fuses related to this system before inspecting the suspected areas below.

Headlight
Symptom	Suspected Area	Link
Both left and right low beam headlights do not illuminate.	Headlight dimmer switch circuit	Click here
Both left and right low beam headlights do not illuminate.	Main body ECU (multiplex network body ECU)	Click here
Low beam headlight on right side does not illuminate.	Headlight unit assembly RH (for ALPHARD)	Click here
	Headlight unit assembly RH (for VELLFIRE)	Click here
	Headlight housing sub-assembly RH (for ALPHARD)	Click here
	Headlight housing sub-assembly RH (for VELLFIRE)	Click here
	Headlight light control ECU sub-assembly RH (sub)	Click here
Low beam headlight on left side does not illuminate.	Headlight unit assembly LH (for ALPHARD)	Click here
	Headlight unit assembly LH (for VELLFIRE)	Click here
	Headlight housing sub-assembly LH (for ALPHARD)	Click here
	Headlight housing sub-assembly LH (for VELLFIRE)	Click here
	Headlight light control ECU sub-assembly LH (main)	Click here
Both left and right high beam headlights do not illuminate.	Headlight dimmer switch circuit	Click here
Both left and right high beam headlights do not illuminate.	Main body ECU (multiplex network body ECU)	Click here
High beam headlight on right side does not illuminate.	High beam headlight circuit	Click here
High beam headlight on right side does not illuminate.	Headlight light control ECU sub-assembly RH (sub)	Click here
High beam headlight on left side does not illuminate.	High beam headlight circuit	Click here
High beam headlight on left side does not illuminate.	Headlight light control ECU sub-assembly LH (main)	Click here
High beam flash function does not operate (high beam headlights are normal).	Headlight dimmer switch circuit	Click here
	Main body ECU (multiplex network body ECU)	Click here
Low beam and high beam headlight on right side does not illuminate.	Power source circuit	Click here
	Headlight light control ECU sub-assembly RH (sub)	Click here
Low beam and high beam headlight on left side does not illuminate.	Power source circuit	Click here
	Headlight light control ECU sub-assembly LH (main)	Click here

Clearance Light (w/o Cornering Light)
Symptom	Suspected Area	Link
Both left and right clearance lights do not illuminate.	Headlight dimmer switch circuit	Click here
Both left and right clearance lights do not illuminate.	Main body ECU (multiplex network body ECU)	Click here
Clearance light on right side does not illuminate.	Clearance light/daytime running light circuit	Click here
Clearance light on right side does not illuminate.	Headlight light control ECU sub-assembly RH (sub)	Click here
Clearance light on left side does not illuminate.	Clearance light/daytime running light circuit	Click here
Clearance light on left side does not illuminate.	Headlight light control ECU sub-assembly LH (main)	Click here

Clearance Light/Daytime Running Light (w/ Cornering Light)
Symptom	Suspected Area	Link
Both left and right clearance light/daytime running lights do not illuminate.	Check customize setting (daytime running light function)	Click here
	Headlight dimmer switch circuit	Click here
	Main body ECU (multiplex network body ECU)	Click here
Clearance light/daytime running light on right side does not illuminate.	Clearance light/daytime running light circuit	Click here
	Headlight light control ECU sub-assembly RH (sub)	Click here
Clearance light/daytime running light on left side does not illuminate.	Clearance light/daytime running light circuit	Click here
	Headlight light control ECU sub-assembly LH (main)	Click here

Front Fog Light
Symptom	Suspected Area	Link
Both left and right front fog lights do not illuminate (taillight is normal).	Headlight dimmer switch circuit	Click here
	Front fog light circuit	Click here
	Main body ECU (multiplex network body ECU)	Click here
Front fog light on one side does not illuminate. (for LED Type)	Fog light assembly	Click here
	Harness or connector	-
Front fog light on one side does not illuminate. (for Bulb Type)	Front fog light bulb	Click here
	Harness or connector	-

Rear Fog Light (w/ Rear Fog Light)
Symptom	Suspected Area	Link
Both left and right rear fog lights do not illuminate (taillight is normal).	Headlight dimmer switch circuit	Click here
	Rear fog light circuit	Click here
	Main body ECU (multiplex network body ECU)	Click here
Rear fog light on one side does not illuminate.	Rear light lens and body (for ALPHARD)	Click here
	Rear light lens and body (for VELLFIRE)	Click here
	Harness or connector	-

License Plate Light
Symptom	Suspected Area	Link
License plate light does not illuminate (taillight is normal).	Harness or connector	-
	License plate light assembly LH	Click here
	License plate light assembly RH	Click here

Taillight
Symptom	Suspected Area	Link
Rear combination light lens and body on right side does not illuminate.	Rear combination light lens and body (for ALPHARD)	Click here
	Rear combination light lens and body (for VELLFIRE)	Click here
	Rear combination light socket and wire sub-assembly (for ALPHARD)	Click here
	Rear combination light socket and wire sub-assembly (for VELLFIRE)	Click here
	Harness or connector	-
	Junction block assembly LH	Click here
Rear combination light lens and body on left side does not illuminate.	Rear combination light lens and body (for ALPHARD)	Click here
	Rear combination light lens and body (for VELLFIRE)	Click here
	Rear combination light socket and wire sub-assembly (for ALPHARD)	Click here
	Rear combination light socket and wire sub-assembly (for VELLFIRE)	Click here
	Harness or connector	-
Taillights other than taillight RH (rear combination light side) do not illuminate (including clearance light and license plate light).	Harness or connector	-
	Junction block assembly LH	Click here
Taillight (rear combination light side) illuminates, but taillight (clearance light side) does not illuminate (including license plate light).	Harness or connector	-
One of the taillight (clearance light side) does not operate.	Rear light lens and body (for ALPHARD)	Click here
	Rear light lens and body (for VELLFIRE)	Click here
	Harness or connector	-
All of the taillights do not operate including clearance light and license plate light assembly.	Headlight dimmer switch circuit	Click here
	Taillight relay circuit	Click here
	Main body ECU (multiplex network body ECU)	Click here

Stop Light System
Symptom	Suspected Area	Link
Stop light on one side does not illuminate.	Rear combination light socket and wire sub-assembly (for ALPHARD)	Click here
	Rear combination light socket and wire sub-assembly (for VELLFIRE)	Click here
	Rear combination light lens and body (for ALPHARD)	Click here
	Rear combination light lens and body (for VELLFIRE)	Click here
	Harness or connector	-
Center stop light does not illuminate.	Harness or connector	-
	Center stop light cord assembly	Click here
	Center stop light assembly	Click here
All of the stop lights do not operate.	Harness or connector	-
All of the stop lights do not operate.	Stop light switch assembly	Click here

Back-up Light
Symptom	Suspected Area	Link
All of the back-up lights do not operate.	Harness or connector	-
	Junction block assembly LH	Click here
	Park/neutral position switch assembly (for Automatic Transaxle)	Click here
	Park/neutral position switch assembly (for CVT)	Click here
Back-up light on one side does not illuminate.	Back-up light bulb	Click here
Back-up light on one side does not illuminate.	Harness or connector	-

Turn Signal Light
Symptom	Suspected Area	Link
No turn signal lights operate (hazard warning lights are normal).	Turn signal switch circuit	Click here
	Combination meter assembly	Click here
One of the turn signal lights does not operate.	Meter / gauge system	Click here

Cornering Light (w/ Cornering Light)
Symptom	Suspected Area	Link
Cornering light on right side does not illuminate.	Cornering light circuit	Click here
Cornering light on right side does not illuminate.	Headlight light control ECU sub-assembly RH (sub)	Click here
Cornering light on left side does not illuminate.	Cornering light circuit	Click here
Cornering light on left side does not illuminate.	Headlight light control ECU sub-assembly LH (main)	Click here

Hazard Warning Light System
Symptom	Suspected Area	Link
Hazard warning lights do not operate (turn signal lights are normal).	Hazard warning switch circuit	Click here
	Combination meter assembly	Click here
Emergency brake signal (hazard warning light blink) does not operate.	CAN communication system (for LHD)	Click here
	CAN communication system (for RHD)	Click here
	Vehicle stability control system	Click here
	Meter / gauge system	Click here

Automatic Light Control System
Symptom	Suspected Area	Link
Automatic light control system does not operate.	Headlight dimmer switch circuit	Click here
Automatic light control system does not operate.	Main body ECU (multiplex network body ECU)	Click here

Light Auto Turn-off System
Symptom	Suspected Area	Link
Light auto turn-off system does not operate.	Headlight dimmer switch circuit	Click here
	Door courtesy switch circuit	Click here
	IG signal circuit	Click here
	Main body ECU (multiplex network body ECU)	Click here

Follow Me Home System (w/o Dimmer Switch OFF Position)
Symptom	Suspected Area	Link
Follow me home system does not operate.	IG signal circuit	Click here
	Headlight dimmer switch circuit	Click here
	Main body ECU (multiplex network body ECU)	Click here