2000 LEXUS GS400 cruise control

I04250

Combination Meter Wiring Circuit ± 1
:Speedometer
:Tachometer
:Fuel Receiver Gauge
:Engine Coolant
Temperature
Receiver Gauge
Speed Control Unit
CLOCK
to GAUGE Fuse
to MPX±B Fuse
to SRS Fuse
Tilt and Telescopic ECU
Body ECU NO.2ECM (GS400)
Ignitor (GS300)
Fuel Main Sender GaugeGround
Fuel Sub Sender Gauge
Light Control Rheostat
Illuminations
ABS, TRAC and VSC ECU
ABS, TRAC and VSC ECU Speed Signal Passenger seat
belt warning
Rr LIGHTS
SEAT BELT
OIL PRESS
OIL LEVEL
DOOR IG+
SRS +BA/T P
A/T R
A/T N
A/T D
A/T 4
A/T 3
A/T 2
A/T L
CRUISE MPX+BIG+IG+
5V
+B
to ECUto
PANEL
Fuse B4
B5
B6
B9
A5
A17A3A8 B16
LCDECU S
T
F
E
Power Source
Brake
Buzzer A11A2 A1 A6
B1
B13
B14A4
B22 ECU
ECU
ECU
S
T
F
E
CHARGE
FUEL LVL
ECT PWR
ECT SNOW TAIL or HEAD
Ground IG+IG+ IG+ IG+
+B
± BODY ELECTRICALCOMBINATION METER
BE±83
2384 Author: Date:
2000 LEXUS GS300/GS400 (RM718U)

IN04S±10
IN±20± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMS
20 Author: Date:
2000 LEXUS GS300/GS400 (RM718U)
HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS
GENERAL INFORMATION
A large number of ECU controlled systems are used in the LEXUS GS400/GS300. In general, the ECU con-
trolled system is considered to be a very intricate system requiring a high level of technical knowledge and
expert skill to troubleshoot. However, the fact is that if you proceed to inspect the circuits one by one, trouble-
shooting of these systems is not complex. If you have adequate understanding of the system and a basic
knowledge of electricity, accurate diagnosis and necessary repair can be performed to locate and fix the
problem. This manual is designed through emphasis of the above standpoint to help service technicians
perform accurate and effective troubleshooting, and is compiled for the following major ECU controlled sys-
tems:
The troubleshooting procedure and how to make use of it are described on the following pages.
SystemPage
1. Engine 2JZ ± GEDI±1
2. Engine 1UZ ± FEDI±156
3. Automatic TransmissionDI±316
4. ABS & Hydraulic Brake Booster Power Supply SystemDI±387
5. Vehicle Skid Control (VSC) & Brake Assist (BA) SystemDI±473
6. Power Tilt and Power Telescopic Steering ColumnDI±517
7. Supplemental Restraint SystemDI±550
8. Power Seat Control SystemDI±683
9. Cruise Control SystemDI±704
10.Engine Immobiliser SystemDI±726
11. Combination Meter SystemDI±744
12.Sliding Roof SystemDI±764
13.Body No. 1 Control SystemDI±776
14.Body No. 2 Control SystemDI±820
15.Driver Door Control SystemDI±856
16.Passenger Door Control SystemDI±889
17.Rear Left Door Control SystemDI±921
18.Rear Right Door Control SystemDI±938
19.Multiplex Communication SystemDI±955
20.LEXUS Navigation SystemDI±1022
21.Air Conditioning SystemDI±1059
FOR USING OBDII SCAN TOOL OR LEXUS HAND±HELD TESTER

Before using the scan tool or tester, the scan tool's instruction book or tester's operator manual should
be read thoroughly.

If the scan tool or tester cannot communicate with ECU controlled systems when you have connected
the cable of the scan tool or tester to DLC3, turned the ignition switch ON and operated the scan tool,
there is a problem on the vehicle side or tool side.
(1) If communication is normal when the tool is connected to another vehicle, inspect the diagnosis
data link line (Bus
line) or ECU power circuit of the vehicle.
(2) If communication is still not possible when the tool is connected to another vehicle, the problem
is probably in the tool itself, so perform the Self Test procedures outline in the Tester Operator's
Manual.

DIAGNOSTIC TROUBLE CODE CHECK PROCEDURE
Diagnostic Trouble
Code Check (Make a
note of and then clear)Confirmation
of SymptomsDiagnostic Trouble
Code CheckProblem Condition
Diagnostic Trouble
Code DisplayProblem symptoms
existSame diagnostic
trouble code is
displayedProblem is still occurring in the diagnostic
circuit
Normal code is
displayedThe problem is still occurring in a place
other than in the diagnostic circuit
(The diagnostic trouble code displayed
first is either for a past problem or it is a
secondary problem)
No problem
symptoms existThe problem occurred in the diagnostic
circuit in the past
Normal Code DisplayProblem symptoms
existNormal code is
displayedThe problem is still occurring in a place
other than in the diagnostic circuit
No problem
symptoms existNormal code is
displayedThe problem occurred in a place other
than in the diagnostic circuit in the past
± INTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED
SYSTEMSIN±23
23 Author: Date:
2000 LEXUS GS300/GS400 (RM718U)
2. SYMPTOM CONFIRMATION AND DIAGNOSTIC TROUBLE CODE CHECK
The diagnostic system in the LEXUS GS400/GS300 fulfills various functions. The first function is the Diag-
nostic Trouble Code Check in which a malfunction in the signal circuits to the ECU is stored in code in the
ECU memory at the time of occurrence, to be output by the technician during troubleshooting. Another func-
tion is the Input Signal Check which checks if the signals from various switches are sent to the ECU correctly.
By using these check functions, the problem areas can be narrowed down quickly and troubleshooting can
be performed effectively. Diagnostic functions are incorporated in the following systems in the LEXUS
GS400/GS300.
SystemDiagnostic Trouble
Code CheckInput Signal Check
(Sensor Check)Diagnostic Test
Mode (Active Test)
Engine (2JZ±GE)
Engine (1UZ±FE)
Automatic Transmission
ABS & Hydraulic Brake Booster Power Supply System
Vehicle Skid Control (VSC) & Brake Assist (BA) System
Power Tilt and Power Telescopic Steering Column
Supplemental Restraint System
Cruise Control System
Engine Immobiliser System
Multiplex Communication System
LEXUS Navigation System
Air Conditioning System(with check Mode)
(with check Mode)
(with check Mode)















In diagnostic trouble code check, it is very important to determine whether the problem indicated by the diag-
nostic trouble code is still occurring or occurred in the past but returned to normal at present. In addition,
it must be checked in the problem symptom check whether the malfunction indicated by the diagnostic
trouble code is directly related to the problem symptom or not. For this reason, the diagnostic trouble codes
should be checked before and after the symptom confirmation to determine the current conditions, as shown
in the table below. If this is not done, it may, depending on the case, result in unnecessary troubleshooting
for normally operating systems, thus making it more difficult to locate the problem, or in repairs not pertinent
to the problem. Therefore, always follow the procedure in correct order and perform the diagnostic trouble
code check.