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Problem Symptoms Table

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.

w/o Adaptive laser cruise control system: 

PROBLEM SYMPTOMS

Symptom Suspect Area See Section
Main switch cannot be turned ON.
(Cruise indicator light in combination meter are not lit.)
  1. Cruise control switch circuit
  2. Spiral cable
  3. Wire harness
  4. Engine system
  5. Combination meter system
  1. CRUISE CONTROL SWITCH CIRCUIT 
  2. DIAGNOSTICS
  3. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  4. BASIC DIAGNOSTIC PROCEDURES
  5. COMBINATION METER SYSTEM - DIAGNOSIS
 
Vehicle speed setting cannot be done.
(Although indicator light is in combination meter lit when the main switch is turned ON, they go off when vehicle speed is set.)
  1. Cruise control switch circuit
  2. Spiral cable
  3. Wire harness
  4. Engine system
  1. CRUISE CONTROL SWITCH CIRCUIT 
  2. DIAGNOSTICS
  3. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  4. BASIC DIAGNOSTIC PROCEDURES
Setting cannot be done.
(Indicator light is in combination meter lit when the main switch is turned ON and they remain ON while setting.)
  1. Cruise control switch circuit
  2. Spiral cable
  3. Stop light switch circuit
  4. PNP switch circuit
  5. Wire harness
  6. Engine system
  7. Combination meter system
  1. CRUISE CONTROL SWITCH CIRCUIT 
  2. DIAGNOSTICS
  3. DTC P0571/52: BRAKE SWITCH "A" Circuit 
  4. DTC P0705: TRANSMISSION RANGE SENSOR CIRCUIT MALFUNCTION (PRNDL INPUT)
  5. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  6. BASIC DIAGNOSTIC PROCEDURES
  7. COMBINATION METER SYSTEM - DIAGNOSIS
While the vehicle is driving with cruise control, the set control is canceled.
(Indicator light and CRUISE remain ON.)
  1. Cruise control switch circuit
  2. Spiral cable
  3. Vehicle speed sensor circuit
  4. Stop light switch circuit
  5. PNP switch circuit
  6. Wire harness
  7. Engine system
  8. Combination meter system
  1. CRUISE CONTROL SWITCH CIRCUIT 
  2. DIAGNOSTICS
  3. DTC P0500/21: VEHICLE SPEED SENSOR "A"; DTC P0503/23: VEHICLE SPEED SENSOR DTC P0503/23: VEHICLE SPEED SENSOR "A" Intermittent/Erratic/High 
  4. DTC P0571/52: BRAKE SWITCH "A" Circuit 
  5. DTC P0705: TRANSMISSION RANGE SENSOR CIRCUIT MALFUNCTION (PRNDL INPUT)
  6. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  7. BASIC DIAGNOSTIC PROCEDURES
  8. COMBINATION METER SYSTEM - DIAGNOSIS
Hunting
(Speed is not constant.)
  1. Vehicle speed sensor circuit
  2. Engine system
  1. DTC P0500/21: VEHICLE SPEED SENSOR "A"; DTC P0503/23: VEHICLE SPEED SENSOR DTC P0503/23: VEHICLE SPEED SENSOR "A" Intermittent/Erratic/High 
  2. BASIC DIAGNOSTIC PROCEDURES
Setting cannot be cancelled.
(When Coast, Acceleration, Resume, Set speed change and control switch are operated.)
  1. Cruise control switch circuit
  2. Spiral cable
  3. Wire harness
  4. Engine system
  1. CRUISE CONTROL SWITCH CIRCUIT 
  2. DIAGNOSTICS
  3. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  4. BASIC DIAGNOSTIC PROCEDURES
No display
  1. Combination meter system
  2. Engine system
  1. COMBINATION METER SYSTEM - DIAGNOSIS
  2. BASIC DIAGNOSTIC PROCEDURES

w/ Adaptive laser cruise control system: 

PROBLEM SYMPTOMS

Main switch cannot be turned ON.
(Cruise indicator light and RADAR READY display in combination meter are not lit.)
  1. Cruise control switch circuit
  2. Spiral cable
  3. Wire harness
  4. Engine system
  5. Combination meter system
  1. CRUISE CONTROL SWITCH CIRCUIT 
  2. DIAGNOSTICS
  3. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  4. BASIC DIAGNOSTIC PROCEDURES
  5. COMBINATION METER SYSTEM - DIAGNOSIS
Setting cannot be done.
(Although indicator light and RADAR READY are lit when the main switch is turned ON, they go off when vehicle speed is set.)
  1. Cruise control switch circuit
  2. Spiral cable
  3. Wire harness
  4. Engine system
  1. CRUISE CONTROL SWITCH CIRCUIT 
  2. DIAGNOSTICS
  3. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  4. BASIC DIAGNOSTIC PROCEDURES
Setting cannot be done.
(Indicator light and RADAR READY are lit when the main switch is turned ON and they remain ON while vehicle speed is set.)
  1. Cruise control switch circuit
  2. Spiral cable
  3. Stop light switch circuit
  4. PNP switch circuit
  5. Wire harness
  6. Engine system
  7. Combination meter system
  1. CRUISE CONTROL SWITCH CIRCUIT 
  2. DIAGNOSTICS
  3. DTC P0571/52: BRAKE SWITCH "A" Circuit 
  4. DTC P0705: TRANSMISSION RANGE SENSOR CIRCUIT MALFUNCTION (PRNDL INPUT)
  5. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  6. BASIC DIAGNOSTIC PROCEDURES
  7. COMBINATION METER SYSTEM - DIAGNOSIS
While the vehicle is driving with cruise control, the set control is canceled.
(Indicator light and RADAR READY remain ON.)
  1. Cruise control switch circuit
  2. Spiral cable
  3. Vehicle speed sensor circuit
  4. Stop light switch circuit
  5. PNP switch circuit
  6. Wire harness
  7. Engine system
  8. Combination meter system
  1. CRUISE CONTROL SWITCH CIRCUIT 
  2. DIAGNOSTICS
  3. DTC P0500/21: VEHICLE SPEED SENSOR "A"; DTC P0503/23: VEHICLE SPEED SENSOR DTC P0503/23: VEHICLE SPEED SENSOR "A" Intermittent/Erratic/High 
  4. DTC P0571/52: BRAKE SWITCH "A" Circuit 
  5. DTC P0705: TRANSMISSION RANGE SENSOR CIRCUIT MALFUNCTION (PRNDL INPUT)
  6. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  7. BASIC DIAGNOSTIC PROCEDURES
  8. COMBINATION METER SYSTEM - DIAGNOSIS
Hunting
(Speed is not constant.)
  1. Vehicle speed sensor circuit
  2. Distance control ECU circuit
  3. Laser radar sensor circuit
  4. Engine system
  1. DTC P0500/21: VEHICLE SPEED SENSOR "A"; DTC P0503/23: VEHICLE SPEED SENSOR DTC P0503/23: VEHICLE SPEED SENSOR "A" Intermittent/Erratic/High 
  2. DTC P1617/63: Distance Control ECU Malfunction 
  3. DTC P1570/73: Laser Radar Sensor Malfunction 
  4. BASIC DIAGNOSTIC PROCEDURES
Setting cannot be cancelled.
(When Coast, Acceleration, Resume, Set speed change and control switch are operated.)
  1. Cruise control switch circuit
  2. Spiral cable
  3. Wire harness
  4. Engine system
  1. CRUISE CONTROL SWITCH CIRCUIT 
  2. DIAGNOSTICS
  3. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  4. BASIC DIAGNOSTIC PROCEDURES
Erroneous detection or lost sight of the vehicle ahead.
  1. Clean laser radar sensor
  2. Improper aiming of laser sensor beam axis
  1. -
  2. DTC P1572/75: Improper Aiming Of Laser Radar Sensor Beam Axis 
DI-918
Alarm buzzer does not sound.
  1. Laser radar buzzer circuit
  2. VSC system
  3. Laser radar sensor circuit
  4. Distance control ECU circuit
  5. Engine system
  1. DTC P1575/66: Warning Buzzer Malfunction 
  2. DIAGNOSIS & TESTING
  3. DTC P1570/73: Laser Radar Sensor Malfunction 
  4. DTC P1617/63: Distance Control ECU Malfunction 
  5. BASIC DIAGNOSTIC PROCEDURES
Set distance cannot be changed.
  1. Combination meter system
  2. Steering pad switch system
  3. Spiral cable
  4. Engine system
  1. CIRCUIT
  2. STEERING PAD SWITCH SYSTEM - DIAGNOSIS
  3. DIAGNOSTICS
  4. BASIC DIAGNOSTIC PROCEDURES
No display.
  1. Combination meter system
  2. Engine system
  1. BASIC DIAGNOSTIC PROCEDURES
  2. BASIC DIAGNOSTIC PROCEDURES
No brake control
(when decelerating)
  1. ABS solenoid circuit
  2. VSC system
  3. Distance control ECU circuit
  4. Engine system
  1. DIAGNOSIS & TESTING
  2. DIAGNOSIS & TESTING
  3. DTC P1617/63: Distance Control ECU Malfunction 
  4. BASIC DIAGNOSTIC PROCEDURES
No shift-down deceleration
  1. Distance control ECU circuit
  2. Engine system
  3. Automatic transmission system
  1. DTC P1617/63: Distance Control ECU Malfunction 
  2. BASIC DIAGNOSTIC PROCEDURES
  3. AUTOMATIC TRANSMISSION - DIAGNOSIS
Constant speed mode cannot be ON.
  1. Cruise control switch circuit
  2. Spiral cable
  3. Wire harness
  4. Engine system
  5. Combination meter system
  1. CRUISE CONTROL SWITCH CIRCUIT 
  2. DIAGNOSTICS
  3. HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE
  4. BASIC DIAGNOSTIC PROCEDURES
  5. CIRCUIT
Vehicle speed setting cannot be cancelled with wiper Lo/Hi.
(Including automatic wiper)
  1. Rain sensor system
  2. Wiper system
  3. Distance control ECU circuit
  4. Engine system
  1. INSPECTION
  2. INSPECTION
  3. DTC P1617/63: Distance Control ECU Malfunction 
  4. BASIC DIAGNOSTIC PROCEDURES
Setting cannot be cancelled in SNOW mode.
  1. Pattern select switch circuit
  2. Automatic transmission system
  3. Engine system
  1. PATTERN SELECT SWITCH CIRCUIT
  2. AUTOMATIC TRANSMISSION - DIAGNOSIS
  3. BASIC DIAGNOSTIC PROCEDURES
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