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Headlight And Taillight System:

WARNING: This page is about a different car, the 2003 Lexus LS 430. However, it is still accessible from the selected car via links, so may be relevant.
HEADLIGHT AND TAILLIGHT SYSTEM SPECIFICATION

Symptom Suspect Area See Section
"LO-beam" headlight does not light up.
  1. Light control switch circuit
  2. Headlight relay circuit
  3. Combination switch
  4. Driver side J/B ECU
  1. LIGHT CONTROL SWITCH CIRCUIT 
  2. HEADLIGHT RELAY CIRCUIT
  3. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  4. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
"HI-beam" headlight does not light up.
  1. Headlight (HI-beam) circuit
  2. Light control switch circuit
  3. Combination switch
  4. Front light ECU
  5. Driver side J/B ECU
  1. HEADLIGHT CIRCUIT
  2. LIGHT CONTROL SWITCH CIRCUIT 
  3. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  4. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  5. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
"Flash" headlight does not light up.
  1. Headlight (Hi-beam) circuit
  2. Light control switch circuit
  3. Combination switch
  4. Front light ECU
  5. Driver side J/B ECU
  1. DI-1203
  2. LIGHT CONTROL SWITCH CIRCUIT 
  3. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  4. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  5. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
Headlight is dark.
  1. Light control switch circuit
  2. Combination switch
  3. Driver side J/B ECU
  1. LIGHT CONTROL SWITCH CIRCUIT 
  2. LIGHT CONTROL SWITCH CIRCUIT 
  3. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
Headlight does not light up or has abnormal operation.
  1. Light control switch circuit
  2. Combination switch
  3. Driver side J/B ECU
  1. LIGHT CONTROL SWITCH CIRCUIT 
  2. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  3. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
Taillight does not light up or has abnormal operation.
  1. Taillight circuit
  2. Light control switch circuit
  3. Combination switch
  4. Luggage room J/B ECU
  5. Driver side J/B ECU
  1. DI-1176
  2. LIGHT CONTROL SWITCH CIRCUIT 
  3. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  4. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  5. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
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