Vehicles With Keyless Entry System
Seat Belt Warning Light: Seat Belt Warning Light does not Work Normally.NOTE: This troubleshooting requires use of scan tool MB991958 and SWS monitor kit MB991862. For details of how to use the SWS monitor, refer to "How to use SWS monitor." How To Use SWS Monitor
Seat Belt Warning Light Circuit Part 1:
Seat Belt Warning Light Circuit Part 2:
CIRCUIT OPERATION
- The ETACS-ECU operates the seat belt warning light according to the following switch signals and input signal:
- Ignition switch (IG1)
- Driver's seat belt switch
- Vehicle speed signal
- If the driver turn the ignition switch to the "ON" position without fastening the seat belt, the seat belt warning light illuminates.
TECHNICAL DESCRIPTION (COMMENT)
If the seat belt warning light does not illuminate, the input circuit, the combination meter (seat belt warning light bulb or printed-circuit board) or the ETACS-ECU may be defective.
TROUBLESHOOTING HINTS
- Malfunction of driver's side seat belt switch
- Malfunction of combination meter (seat belt warning light bulb or printed-circuit board)
- Malfunction of the ETACS-ECU
DIAGNOSIS
Required Special Tools:
- MB991223: Harness Set
- MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: Vehicles communication interface
- MB991827: MUT-III USB cable
- MB991911: MUT-III Main harness B
- MB991813: SWS monitor kit
- MB991806: SWS monitor cartridge
- MB991812: SWS monitor harness (for column-ECU)
- MB991922: Probe harness
STEP 1. Use scan tool MB991958 to select "ECU COMM Check" on the SWS monitor display.
Check the ETACS-ECU.
CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958. Connect special tool MB991911 before connecting 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." How to Connect SWS Monitor
2. Turn the ignition switch to the "LOCK" (OFF) position.
3. Operate scan 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. Scan tool MB991958 should show "OK" on the "ECU COMM Check" menus for both the "ETACS ECU" menus.
Q: Is "OK" displayed on the "ETACS ECU" menu?
YES: Go to Step 2.
NO: Refer to Inspection Procedure A-3 "Communication with ETACS-ECU is impossible."
STEP 2. Check the input signal by using "DATA LIST" of the SWS monitor.
Turn the ignition switch to the "ON" position before checking input signals from the ignition switch (IG1).
1. Operate scan tool MB991958 according to the procedure below to display "ETACS ECU."
a. Select "Interactive Diagnosis."
b. Select "System select."
c. Select "SWS."
d. Select "SWS MONITOR."
e. Select "Data List."
f. Select "ETACS ECU."
2. Check that normal conditions are displayed on the items described in the given table.
Q: Does the scan tool display "IG SW (IG1)" as normal condition?
YES: Go to Step 3.
NO: Refer to Inspection Procedure O-2 "ETACS-ECU does not receive a signal from the ignition switch (IG1)."
STEP 3. Check the input signal (by using the Pulse check mode of the monitor).
Check input signal from the driver's side seat belt switch.
1. Operate scan tool MB991958 according to the procedure below to display "Pulse check."
a. Select "Interactive Diagnosis."
b. Select "System select."
c. Select "SWS."
d. Select "Pulse Checking."
2. When the driver's seat belt is fastened, check if scan tool MB991958 sounds or not.
Q: Does scan tool MB991958 sound when the driver's side seat belt is fastened?
YES: Go to Step 4.
NO: Refer to Inspection Procedure P-3 "ETACS-ECU does not receive a signal from the driver's side seat belt switch."
STEP 4. Check the input signal (by using the Pulse check mode of the monitor).
Check the input signals from the vehicle speed sensor.
1. Operate scan tool MB991958 according to the procedure below to display "Pulse check."
a. Select "Interactive Diagnosis."
b. Select "System select."
c. Select "SWS."
d. Select "Pulse Checking."
2. When the vehicle speed exceeds 10 km/h (6.2 mph), check that scan tool MB991958 sounds or not.
Q: Does scan tool MB991958 sound when the vehicle speed exceeds 10 km/h (6.2 mph)?
YES: Go to Step 5.
NO: Refer to Inspection Procedure P-11 "ETACS-ECU does not receive a signal from the vehicle speed sensor."
STEP 5. Check at ETACS-ECU connector C-118 in order to check the ground circuit to the seat belt warning light.
1. Disconnect ETACS-ECU connector C-118, and measure at the wiring harness side.
2. Turn the ignition switch to the "ON" position.
3. Connect terminal 73 to ground.
Q: Does the seat belt warning light illuminate?
YES: Replace the ETACS-ECU. Check that the seat belt warning light illuminates normally.
NO: Go to Step 6.
STEP 6. Check the seat belt warning light bulb.
Q: Is the seat belt warning light bulb in good condition?
YES: Go to Step 7.
NO: Replace the bulb. Check that the seat belt warning light illuminates normally.
STEP 7. Check the combination meter (printed-circuit board).
1. Remove the combination meter.
2. Remove the seat belt warning light bulb. Then measure the resistance value between the bulb terminals.
3. Install the bulb to the combination meter, and then measure the resistance value between connector C-41 terminal 52 and connector C-42 terminal 27. The measured resistance value should be roughly the same as the value measured in Step (2).
Q: Are these two resistance values extremely different?
YES: Repair or replace the combination meter (printed circuit board). Check that the seat belt warning light illuminates normally.
NO (much the same): Go to Step 8.
STEP 8. Measure at combination meter connector C-41 in order to check the ignition switch (IG1) line of the power supply to the combination meter.
1. Disconnect combination meter connector C-41, and measure at the wiring harness side.
2. Turn the ignition switch to the "ON" position.
3. Measure the voltage between terminal 52 and ground.
- The measured value should be approximately 12 volts (battery positive voltage).
Q: Does the measured voltage correspond with this range?
YES: Go to Step 11.
NO: Go to Step 9.
STEP 9. Check combination meter connector C-41 for damage.
Q: Is combination meter connector C-41 in good condition?
YES: Go to Step 10.
NO: Repair or replace the connector. Refer to Harness Connector Inspection. Check that the seat belt warning light illuminates normally.
STEP 10. Check the wiring harness between combination meter connector C-41 (terminal 52) and the ignition switch (IG1).
NOTE: Also check junction block connectors C-108 and C-111. If junction block connector C-108 or C-111 is damaged, repair or replace the connector as described in Harness Connector Inspection.
Q: Is the wiring harness between combination meter connector C-41 (terminal 52) and the ignition switch (IG1) in good condition?
YES: No action to be taken.
NO: Repair the wiring harness. Check that the seat belt warning light illuminates normally.
STEP 11. Check combination meter connector C-42 and ETACS-ECU connector C-118 for damage.
Q: Are combination meter connector C-42 and ETACS-ECU connector C-118 in good condition?
YES: Go to Step 12.
NO: Repair or replace the connector. Refer to Harness Connector Inspection. Check that the seat belt warning light illuminates normally.
STEP 12. Check the wiring harness between combination meter connector C-42 (terminal 27) and ETACS-ECU connector C-118 (terminal 73).
Q: Is the wiring harness between combination meter connector C-42 (terminal 27) and ETACS-ECU connector C-118 (terminal 73) in good condition?
YES: No action to be taken.
NO: Repair the wiring harness. Check that the seat belt warning light illuminates normally.