Page 69 of 1500

SYMPTOM PROCEDURES
SIMPLIFIED WIRING SYSTEM (SWS)54B-69
STEP 1. Use diagnostic tool MB991958 to select "ECU 
COMM Check" on the SWS monitor display. 
Check the following ECUs:
ETACS-ECU
Column-ECU
To prevent damage to diagnostic tool MB991958, always 
turn the ignition switch to the "LOCK" (OFF) position 
before connecting or disconnecting diagnostic tool 
MB991958. Connect special tool MB991910 before con-
necting special tool MB991812. Be sure to connect special 
tool MB991806 after turning on special tool MB991824.
(1) Connect the special tool. Refer to "How to connect SWS 
monitor P.54B-13."
(2) Turn the ignition switch to the "ON" position.
(3) Operate diagnostic tool MB991958 according to the 
procedure below to display "ECU COMM Check."
a. Select "Interactive Diagnosis."
b. Select "System select."
c. Select "SWS."
d. Select "SWS MONITOR."
e. Select "ECU COMM Check."
(4) DIAGNOSTIC TOOL MB991958 should show "OK" on the 
"ECU COMM Check" menus for both the "ETACS ECU" 
and the "COLUMN ECU" menus.
Q: Is "OK" displayed for both the "ETACS ECU" and 
"COLUMN ECU" menus?
"OK" is displayed for all the items : Go to Step 2.
"NG" is displayed for the "COLUMN ECU" menu : Go to 
St e p  6 .
"NG" is displayed for the "ETACS ECU" menu : Refer to 
Inspection Procedure A-3 "Communication with the 
ETACS-ECU is not possible P.54B-74."
"NG" is displayed for all the items : Refer to Inspection 
Procedure A-3 "Communication with the ETACS-ECU 
is not possible P.54B-74." 
         
        
        
     
        
        Page 74 of 1500

SYMPTOM PROCEDURES
SIMPLIFIED WIRING SYSTEM (SWS)54B-74
INSPECTION PROCEDURE A-3: Communication with the ETACS-ECU is not Possible.
.
CIRCUIT OPERATION
The power supply to the ETACS-ECU is provided 
by the battery and the ignition switch (IG1).
If the power supply system from the battery is 
defective, the system operates by the power sup-
ply from the ignition switch (IG1).
Refer to circuit diagrams GROUP-90
Refer to configuration diagrams GROUP-80
.
TECHNICAL DESCRIPTION (COMMENT)
It is suspected that the power supply circuit to the 
ETACS-ECU is defective, or the wiring harness 
between the SWS monitor kit and the ETACS-ECU 
or their connector(s) is damaged. If the battery power 
supply circuit to the ECU (terminal 20 of the ETACS-ECU) is damaged, also check the power 
supply circuit from the ignition switch (IG1) (terminal 
8 of the ETACS-ECU), and repair if necessary. If the 
ground circuit to the ECU (terminal 3 of the 
ETACS-ECU) is damaged, also check the ground cir-
cuit to the sensor (terminal 50 of the ETACS-ECU), 
and repair if necessary.
.
TROUBLESHOOTING HINTS
The wiring harness or connectors may have 
loose, corroded, or damaged terminals, or termi-
nals pushed back in the connector
The ETACS-ECU may be defective
DIAGNOSIS
Required Special Tools:
MB991223: Harness Set
MB991958: DIAGNOSTIC TOOL (MUT-III Sub Assembly)
MB991824: Vehicle Communication Interface (V.C.I.)
MB991827: MUT-III USB Cable
MB991910: MUT-III Main Harness A 
         
        
        
     
        
        Page 80 of 1500

SYMPTOM PROCEDURES
SIMPLIFIED WIRING SYSTEM (SWS)54B-80
INSPECTION PROCEDURE A-4: Communication with the Front-ECU is not Possible.
NOTE: This troubleshooting procedure requires the 
use of diagnostic tool MB991958 and SWS monitor 
kit MB991813. For details on how to use the SWS 
monitor, refer to "How to connect SWS monitor 
P.54B-13."
.
CIRCUIT OPERATION
The power supply to the front-ECU is provided by 
the battery and the ignition switch (IG2).
If the power supply system from the battery is 
defective, the system operates by the power sup-
ply from the ignition switch (IG2).
Refer to circuit diagrams GROUP-90
Refer to configuration diagrams GROUP-80
.
TECHNICAL DESCRIPTION (COMMENT)
It is suspected that the power supply circuit to the 
front-ECU is defective, or the wiring harness 
between the SWS monitor kit and the front-ECU or 
their connector(s) is damaged. If the battery power 
supply circuit to the ECU (terminal 5 of the 
front-ECU) is damaged, also check the power supply 
circuit from the ignition switch (IG2) (terminal 22 of 
the front-ECU), and repair if necessary.
.
TROUBLESHOOTING HINTS
The wiring harness or connectors may have 
loose, corroded, or damaged terminals, or termi-
nals pushed back in the connector
The front-ECU may be defective
The ETACS-ECU may be defective 
         
        
        
     
        
        Page 82 of 1500

SYMPTOM PROCEDURES
SIMPLIFIED WIRING SYSTEM (SWS)54B-82
STEP 1. Use diagnostic tool MB991958 to select "ECU 
COMM Check" on the SWS monitor display. 
Check the ETACS-ECU.
To prevent damage to diagnostic tool MB991958, always 
turn the ignition switch to the "LOCK" (OFF) position 
before connecting or disconnecting diagnostic tool 
MB991958. Connect special tool MB991910 before con-
necting special tool MB991812. Be sure to connect special 
tool MB991806 after turning on special tool MB991824.
(1) Connect the special tool. Refer to "How to connect SWS 
monitor P.54B-13."
(2) Turn the ignition switch to the "LOCK" (OFF) position.
(3) Operate diagnostic tool MB991958 according to the 
procedure below to display "ECU COMM Check."
a. Select "Interactive Diagnosis."
b. Select "System select."
c. Select "SWS."
d. Select "SWS MONITOR."
e. Select "ECU COMM Check."
(4) DIAGNOSTIC TOOL MB991958 should show "OK" on the 
"ECU COMM Check" menu for the "ETACS ECU" menu.
Q: Is "OK" displayed for the "ETACS ECU" menu?
YES : Go to Step 2.
NO : Refer to Inspection Procedure A-3 "Communication 
with the ETACS-ECU is not possible P.54B-74." 
         
        
        
     
        
        Page 87 of 1500
SYMPTOM PROCEDURES
SIMPLIFIED WIRING SYSTEM (SWS)54B-87
INSPECTION PROCEDURE A-5: Communication with the Sunroof-ECU is not Possible.
.
CIRCUIT OPERATION
Power to the sunroof motor assembly is supplied 
through fusible link (5).
When the ignition switch (IG2) signal is on, the 
sunroof motor assembly is ready to operate.
Refer to circuit diagrams GROUP-90
Refer to configuration diagrams GROUP-80
.
TECHNICAL DESCRIPTION (COMMENT)
The power supply circuit or the communication circuit 
to the sunroof motor assembly or the sunroof motor 
assembly may be defective.
.
TROUBLESHOOTING HINTS
The wiring harness or connectors may have 
loose, corroded, or damaged terminals, or termi-
nals pushed back in the connector
The sunroof motor assembly may be defective
The ETACS-ECU may be defective 
         
        
        
     
        
        Page 91 of 1500
SYMPTOM PROCEDURES
SIMPLIFIED WIRING SYSTEM (SWS)54B-91
STEP 4. Check the ignition switch (IG2) circuit to the 
sunroof motor assembly. Measure the voltage at sunroof 
motor assembly connector D-04.
(1) Disconnect sunroof motor assembly connector D-04 and 
measure the voltage available at the wiring harness side of 
the connector.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal 2 and ground.
The voltage should measure approximately 12 volts 
(battery positive voltage).
Q: Is the measured voltage approximately 12 volts (battery 
positive voltage)?
YES : Go to Step 6.
NO : Go to Step 5.
STEP 5. Check the wiring harness between sunroof motor 
assembly connector D-04 (terminal 2) and ignition switch 
(IG2). 
         
        
        
     
        
        Page 92 of 1500

SYMPTOM PROCEDURES
SIMPLIFIED WIRING SYSTEM (SWS)54B-92
NOTE: Also check junction block connectors C-215 and C-205 
for loose, corroded, or damaged terminals, or terminals pushed 
back in the connector. If junction block connector C-215 or 
C-205 is damaged, repair or replace the damaged compo-
nent(s) as described in GROUP 00E, Harness Connector 
Inspection P.00E-2.
Q: Is the wiring harness between sunroof motor assembly 
connector D-04 (terminal 2) and the ignition switch (IG2) 
in good condition?
YES : No action is necessary and testing is complete.
NO : The wiring harness may be damaged or the 
connector(s) may have loose, corroded or damaged 
terminals, or terminals pushed back in the connector. 
Repair the wiring harness as necessary. The system 
should communicate with the sunroof-ECU normally.
STEP 6. Check the ground circuit to the sunroof motor 
assembly. Measure the resistance at sunroof motor 
assembly connector D-04.
(1) Disconnect sunroof motor assembly connector D-04 and 
measure the resistance available at the wiring harness side 
of the connector.
(2) Measure the resistance value between terminal 5 and 
ground.
The resistance should be 2 ohms or less.
Q: Is the measured resistance 2 ohms or less?
YES : Go to Step 8.
NO : Go to Step 7. 
         
        
        
     
        
        Page 96 of 1500

SYMPTOM PROCEDURES
SIMPLIFIED WIRING SYSTEM (SWS)54B-96
If any of the following conditions is met with the igni-
tion switch at "ON" or "ST", the ETACS-ECU sounds 
the tone alarm by using the driver's seat belt switch 
signal and the vehicle speed signal sent from the 
combination meter.
Sounds the tone alarm for six seconds when the 
ignition switch is turned "ON" with the seat belt 
switch on (the driver's seat belt is not fastened). 
This is called "Timer function".
Sounds the tone alarm 12 cycles (after 0.5 sec-
onds) if any of the following conditions is met 
when sixty seconds or more have elapsed since 
the ignition switch is turned "ON". One cycle con-
sists of five-second "on" and then three-second 
"off".a. The vehicle speed has reached 8 km/h (5 
mph) while the seat belt switch is turned on 
(driver's seat belt is not fastened) with the 
ignition switch "ON.
b. The seat belt switch has been turned on 
(driver's seat belt has not been fastened) for 
at least ten seconds while the ignition switch 
has been turned "ON" and the vehicle speed 
has been 8 km/h (5 mph) or more.
NOTE: Once the tone alarm has sounded 12 
cycles, it does not sound again until the vehi-
cle speed reduces to 3 km/h (2 mph) or less 
even if any of the following conditions is met.
The tone alarm stops sounding if the ignition 
switch or the seat belt switch is turned off (the 
driver's seat belt is fastened) while the timer 
operation is active.