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DTC B1537: Seat Belt Switch (Passenger’s side) Circuit Open
DTC B1538: Seat Belt Switch (Passenger’s side) Circuit (Ground Side) Shorted
 
 

cautionIf DTC B1537 or B1538 are 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 location 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.
 
 
TROUBLESHOOTING HINTS
  • Malfunction of the seat belt switch (passenger’s side)
  • Damaged wiring harnesses or connectors
  • Malfunction of the SRS-ECU
 
 
DIAGNOSIS
STEP 1. Using scan tool MB991958, diagnose the CAN bus line.
(1)
cautionTo prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
Connect scan tool MB991958. Refer to "How to connect the scan tool ."
(2) Connect scan tool MB991958 to the data link connector.
(3) Turn the ignition switch to the "ON" position.
(4) Diagnose the CAN bus line.
(5) 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 3.
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 (passenger’s side) connector D-40 and the SRS-ECU connector C-125.
(1) Disconnect the negative battery terminal.
(2) Disconnect the seat belt switch (passenger’s side) connector D-40.
(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 C-125 SRS-ECU connector.
(4) Measure the resistance between terminal 53, 58 and body ground (No. B1537 only).It should be an open circuit.

(5) Connect the negative battery terminal.
(6) Ignition switch: ON.
(7) Measure the voltage between terminal 33, 38 and body ground (No. B1538 only).Voltage should measure 1 volt or less.
Is the check result normal?
Go to Step 5.
Go to Step 4.
 
STEP 4. Check the harness wires between SRS-ECU connector C-125 (terminal No.33 and 38) and the seat belt switch (passenger’s side) connector D-40 (terminal No.1 and 2) (No. B1537 only).
Is the check result normal?
Go to Step 6.
Repair the harness wires between SRS-ECU connector C-125 and the seat belt switch (passenger’s side) connector D-40. Then go to Step 6.
 
STEP 5. Check the harness wires between SRS-ECU connector C-125 (terminal No.33 and 38) and the seat belt switch (passenger’s side) connector D-40 (terminal No.2 and 1).
(1) Disconnect the negative battery terminal.
(2) 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 C-125 SRS-ECU connector.
(3) Disconnect the seat belt switch (passenger’s side) connector D-40.
(4)
cautionDo not insert a probe into the terminal from D-40 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.
  • SRS-ECU connector C-125 (terminal No.33) and the seat belt switch (passenger’s side) connector D-40 (terminal No.2)
  • SRS-ECU connector C-125 (terminal No.38) and the seat belt switch (passenger’s side) connector D-40 (terminal No.1)
Is the check result normal?
go to Step 6.
Repair harness wires between SRS-ECU connector C-125 and the seat belt switch (passenger’s side) connector D-40.
 
STEP 6. Seat belt switch (passenger’s side) check.
Refer to GROUP 52A, Front Seat Belt
Is the check result normal?
Go to Step 7.
Replace the seat belt switch (passenger’s side) (Refer to GROUP 52A, Front Seat Belt ).
 
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 B1537 or B1538 set?
Replace the SRS-ECU (Refer to ).
The procedure is complete.