LEXUS LS430 2003 Factory Repair Manual

Fig. 59: Identifying Laser Sensor Terminals
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
c. Check the signal waveform between terminal LRDD (L1-3) of the laser sensor and body ground.
OK:
A waveform similar to that in the illustration to the left is output.
HINT:
Gauge set: 1 V/DIV, 2 ms/DIV
Condition: Ignition switch ON
NG: REPLACE LASER SENSOR (SEE REPLACEMENT
)

Fig. 60: Signal Waveform Graph
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
OK: REPLACE CRUISE CONTROL ECU ASSY (SEE REPLACEMENT
)
CIRCUIT DESCRIPTION
The laser sensor and cruise control ECU (distance control ECU) transmit the data for general vehicle control
and diagnosis function along the communication line.
The cruise control ECU (distance control ECU) determines the presumed R information based on the signal
from the steering wheel and yaw rate sensor.
The cruise control ECU (distance control ECU) transmits the current vehicle speed and presumed R information
to the laser sensor.

Fig. 61: DTC U1102 Problem Symptom Diagnostic Chart
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
WIRING DIAGRAM
Fig. 62: Wiring Diagram
- Lost Communication With Radar Sensor
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INSPECTION PROCEDURE
1.CHECK WIRE HARNESS AND CONNECTOR (DISTANCE CONTROL ECU - LASER
SENSOR)
a. Disconnect the distance control ECU and laser sensor connectors.
b. Measure the resistance according to the value(s) in the table below.
Standard:
DISTANCE CONTROL ECU AND LASER SENSOR CONNECTOR TERMINALS
RESISTANCE SPECIFICATION
Tester connectionConditionSpecified value
D2-23 (LRRD) - L1-4 (LRRD)AlwaysBelow 1 ohms
D2-13 (IGB) - L1-5 (IGB)AlwaysBelow 1 ohms
D2-23 (LRRD) - Body groundAlways10 kohms or higher
D2-13 (IGB) - Body groundAlways10 kohms or higher

Fig. 63: Disconnecting Distance Control ECU Connector
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

Fig. 64: Disconnecting Laser Sensor Connector
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
NG: REPAIR OR REPLACE WIRE HARNESS OR CONNECTOR
OK: Go To Next Step.
2.INSPECT CRUISE CONTROL ECU ASSY (DISTANCE CONTROL ECU)
a. Reconnect the cruise control ECU (distance control ECU) connector.
b. Turn the ignition switch to the ON position.
c. Measure the voltage according to the value(s) in the table below.
Standard:
CRUISE CONTROL ECU TERMINALS VOLTAGE SPECIFICATION
Tester connectionConditionSpecified value
D2-13 (IGB) - Body groundIgnition SW ON10 to 14 V

Fig. 65: Identifying Cruise Control ECU Terminals
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
d. Check the signal waveform between terminal LRRD (D2-23) of the cruise control ECU (distance
control ECU) and body ground.
OK:
A waveform similar to that in the illustration to the left is output.
HINT:
Gauge set: 2 V/DIV, 5 ms/DIV
Condition: Ignition switch ON
NG: REPLACE CRUISE CONTROL ECU ASSY (SEE REPLACEMENT
)

Fig. 66: Signal Waveform Graph
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
OK: REPLACE LASER SENSOR (SEE REPLACEMENT
)
CIRCUIT DESCRIPTION
The laser sensor emits laser beams towards an object in front and measures the distance and direction of the
object by receiving the beam reflections. Based on the reflections, the sensor calculates the difference in speed
between your own vehicle and on object in front. This data is transmitted to the cruise control ECU (distance
control ECU).
DTC P1570 PROBLEM SYMPTOM DIAGNOSTIC
HINT:
DTC No.Detection ItemTrouble Area
P1570The ECM outputs this trouble code when it detects the communication
error signal (from the cruise control ECU (distance control ECU) to the
laser sensor) for 0.15 sec. or more while the dynamic laser cruise control
is in operation.laser sensor

The laser sensor monitors the laser emission and reception by itself. This DTC is detected when it cannot
monitor.
When rain drops or snowflakes strike the laser sensor face, the distance between the vehicle in front and your
own vehicle cannot be measured correctly.
The dynamic laser cruise control system functions by detecting the reflector of the vehicle directly in front. In
the following cases, the system may not be able to detect the vehicle in front and may not properly maintain the
correct vehicle-to-vehicle distance.
The vehicle in front is a tall trailer.
The back of the vehicle in front is extremely dirty.
Emissions from the vehicle in front or from other lanes are heavy.
The vehicle in front has no reflector.
The laser sensor is receiving a strong flash of light (sunlight, etc.).
INSPECTION PROCEDURE
1.ADJUST LASER SENSOR (SEE ADJUSTMENT
)
HINT:
It is necessary to make the ECM recognize spec information (whether the vehicle is equipped with the
dynamic laser or not). When this procedure has not been carried out, this DTC may be output.
1. Clear the DTC and then recheck for DTCs.
OK: DTC is not output.
HINT:
If DTC P1570 is still output after performing the above procedures, replace the laser sensor.
NG: REPLACE LASER SENSOR (SEE REPLACEMENT
)
OK: SYSTEM OK
CIRCUIT DESCRIPTION
This DTC is output when the scanning angle of the laser sensor is incorrect.
This DTC is also output when the laser sensor optical axis is in an incorrect position is detected.
DTC P1572 PROBLEM SYMPTOM DIAGNOSTIC

HINT:
If the optical axis deviates to the upper/lower side +/-2° or more and/or the right/left side +/-4° or more, this
DTC is detected.
INSPECTION PROCEDURE
1.ADJUST LASER SENSOR (SEE ADJUSTMENT
)
CIRCUIT DESCRIPTION
This circuit detects the angle and direction of steering and automatically transmits its signal to the skid control
ECU and distance control ECU.
Fig. 67: DTC U0126 Problem Symptom Diagnostic Chart

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INSPECTION PROCEDURE
HINT:
This circuit uses CAN for communication. Therefore, if there are any malfunctions in the communication
circuit, one or more DTCs in the CAN communication system is/are output.
1.GO TO CAN COMMUNICATION SYSTEM (SEE HOW TO PROCEED WITH
TROUBLESHOOTING )
CIRCUIT DESCRIPTION
DTC
No.DTC Detection ConditionTrouble
Area
P1572
The ECM outputs this trouble code when the ECU detects that the laser sensor optical
axis is in an incorrect position (0.15 sec. or more) while dynamic laser cruise control
is in operation.laser
sensor

This circuit detects the yaw rate of the vehicle and transmits its signal to the skid control ECU and distance
control ECU.
Fig. 68: DTC U0123 Problem Symptom Diagnostic Chart

Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
INSPECTION PROCEDURE
HINT:
This circuit uses CAN for communication. Therefore, if there are any malfunctions in the communication
circuit, one or more DTCs in the CAN communication system is/are output.
1.GO TO CAN COMMUNICATION SYSTEM (SEE HOW TO PROCEED WITH
TROUBLESHOOTING )
CIRCUIT DESCRIPTION
This circuit provides power to operate the cruise control ECU (distance control ECU). The distance control
ECU determines the vehicle that you are following based on data from the laser sensor and then decides how
much acceleration and/or deceleration is needed to maintain the set distance. It also requests the skid control
ECU to apply braking and sound the buzzer.
WIRING DIAGRAM