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DTC B1520: Seat belt switch (driver’s side) malfunction
DTC B1527: Seat belt switch (driver’s side) circuit open
DTC B1528: Seat belt switch (driver’s side) circuit (ground side) shorted
DTC B1529: Seat belt switch (driver’s side) system fault power supply circuit (short-circuited to power supply)
 
 
cautionIf DTC B1520, B1527, B1528 or B1529 is set in the SRS-ECU, always diagnose the CAN main bus lines.
 
 
CIRCUIT OPERATION
The SRS-ECU determines whether the seat belt is fastened or not according to the connection of the seat belt switch in the seat buckle.
 
 
DTC SET CONDITIONS
The DTC is set when the seat belt switch output current is not within the specified range.
Cause of trouble for each DTC is as follows.
DTCSYMPTOM
B1520Malfunction of seat belt switch
B1527Malfunction of the common terminal or open circuit in its harness
B1528Short to body ground in the common terminal harness
B1529Short to the power supply in the seat belt switch harness
 
 
TROUBLESHOOTING HINTS
  • Damaged wiring harnesses or connectors
  • Malfunction of the seat belt switch (driver’s side)
  • Malfunction of the SRS-ECU
 
 
DIAGNOSIS
STEP 1. Using scan tool (M.U.T.-III), diagnose the CAN bus line.
(1)
cautionTo prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
Connect scan tool (M.U.T.-III). Refer to "How to connect the scan tool ."
(2) Turn the ignition switch to the "ON" position.
(3) Diagnose the CAN bus line.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the CAN bus line found to be normal?
Go to Step 2.
Repair the CAN bus line (Refer to GROUP 54C, Diagnosis ).
 
STEP 2. Recheck for diagnostic trouble code.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn the ignition switch to "ON" position.
(3) Check if the DTC is set.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the DTC set?
Go to Step 6 (DTC B1520).
Go to Step 3 (DTC B1527).
Go to Step 4 (DTC B1528).
Go to Step 5 (DTC B1529).
There is an intermittent malfunction such as poor engaged connector(s) or open circuit (Refer to GROUP 00, How to Cope with Intermittent Malfunction ).
 
STEP 3. Check the harness short circuit between seat belt switch (driver’s side) connector and the SRS-ECU connector.
(1) Disconnect the negative battery terminal.
(2) Disconnect the seat belt switch (driver’s side) connector.
(3) While pushing the part "A" indicated in the figure of the harness side connector, turn the lock lever to the direction of the arrow to release the lock lever, and disconnect the SRS-ECU connector.
(4)
cautionDo not insert a probe into the terminal from seat belt switch (driver’s side) connector harness side connector front side directly, as the connector contact pressure may be weakened.
Check for continuity between the following terminals. It should be less than 2 ohms.
  • Continuity DBS- line between SRS-ECU wiring harness side connector and the seat belt switch (driver’s side) connector
  • Continuity DBSO line between SRS-ECU wiring harness side connector and the seat belt switch (driver’s side) connector
Is the check result normal?
Go to Step 6.
Repair the harness wires DBS-, DBSO line between SRS-ECU connector and the seat belt switch (driver’s side) connector. Then go to Step 7.
 
STEP 4. Check the harness short circuit between seat belt switch (driver’s side) connector and the SRS-ECU connector.
(1) Disconnect the negative battery terminal.
(2) Disconnect the seat belt switch (driver’s side) connector.
(3) While pushing the part "A" indicated in the figure of the harness side connector, turn the lock lever to the direction of the arrow to release the lock lever, and disconnect the SRS-ECU connector.
(4) Measure the resistance between DBS-, DBSO line and body ground. It should be less than 2 ohms.
Is the check result normal?
Go to Step 6.
Repair the harness wires DBS-, DBSO line between SRS-ECU connector and the seat belt switch (driver’s side) connector. Then go to Step 7.
 
STEP 5. Check the harness short circuit between seat belt switch (driver’s side) connector and the SRS-ECU connector.
(1) Disconnect the negative battery terminal.
(2) Disconnect the seat belt switch (driver’s side) connector.
(3) While pushing the part "A" indicated in the figure of the harness side connector, turn the lock lever to the direction of the arrow to release the lock lever, and disconnect the SRS-ECU connector.
(4) Connect the negative battery terminal.
(5) Ignition switch: ON.
(6) Measure the voltage between DBS-, DBSO line and body ground. Voltage should measure 1 volt or less.
Is the check result normal?
Go to Step 6.
Repair the harness wires DBS-, DBSO line between SRS-ECU connector and the seat belt switch (driver’s side) connector. Then go to Step 7.
 
STEP 6. Seat belt switch (driver’s side) check.
Checked whether the seat belt switch (driver’s side) is normal (Refer to GROUP 52A, Front Seat Belt ).
Is the check result normal?
Go to Step 7.
Replace the inner seat belt (driver’s side) (Refer to GROUP 52A, Front Seat Assembly ).
 
STEP 7. Recheck for diagnostic trouble code.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn the ignition switch to the "ON" position.
(3) Check if the DTC is set.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is DTC B1520, B1527, B1528 or B1529 set?
Replace the SRS-ECU (Refer to ).
The procedure is complete.