B1B54

DTC B1B54: Seat Belt Buckle Switch (RH) Circuit (Ground Side) Shorted
DTC B1B55: Seat Belt Buckle Switch (RH) Circuit (Power Supply Side) Shorted
DTC B1B56: Seat Belt Buckle Switch
(RH) Circuit Open













CAUTION:
If DTC B1B54, B1B55 or B1B56 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 buckle switch in the seat buckle.

DTC SET CONDITIONS

The DTC is set when the seat belt buckle switch output current is not within the specified range.

TROUBLESHOOTING HINTS

- Malfunction of the seat belt buckle switch
- Damaged wiring harnesses or connectors
- Malfunction of the SRS-ECU


DIAGNOSIS

Required Special Tools:

- MB991222: Probe
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)

STEP 1. Using scan tool MB991958, diagnose the CAN bus line.





(1)
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 scan tool MB991958. Refer to "How to connect the scan tool Reading and Clearing Diagnostic Trouble Codes."
(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.

Q. Is the CAN bus line found to be normal?

YES Go to Step 2.

NO Repair the CAN bus line CAN Bus Diagnostics Chart).

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.

Q. Is the DTC set?

YES Go to Step 3.
NO There is an intermittent malfunction such as poor engaged connector(s) or open circuit How to Cope With Intermittent Malfunctions).
STEP 3. Check the harness short circuit between seat belt buckle switch
(passenger's side) connector D-37 and the SRS-ECU connector C-36.

(1)Disconnect the negative battery terminal.

(2)Disconnect the seat belt buckle switch (passenger's side) connector D-37.





(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-36 SRS-ECU connector.





(4)Measure the resistance between terminal 55, 58 and body ground (No. B1B54 only).
It should be an open circuit.
(5)Connect the negative battery terminal.
(6)Ignition switch: ON.





(7)Measure the voltage between terminal 55, 58 and body ground (No. B1B55 only).
Voltage should measure 1 volt or less.

Q. Is the check result normal?

YES Go to Step 5.

NO Go to Step 4.

STEP 4. Check the harness wires between SRS-ECU connector C-36 (terminal No.55 and 58) and the seat belt buckle switch (passenger's side) connector D-37 (terminal No.1 and 2).

Q. Is the check result normal?

YES Go to Step 6.
NO Repair the harness wires between SRS-ECU connector C-36 and the seat belt buckle switch (passenger's side) connector D-37. Then go to Step 6.
STEP 5. Check the harness wires between SRS-ECU connector C-36 (terminal No.55 and 58) and the seat belt buckle switch (passenger's side) connector D-37 (terminal No.1 and 2).

(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-36 SRS-ECU connector.
(3)Disconnect the seat belt buckle switch (passenger's side) connector D-37.





(4)
CAUTION:
Do not insert a probe into the terminal from D-37 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 [No.B1B56].

- SRS-ECU connector C-36 (terminal No.55) and the seat belt buckle switch (passenger's side) connector D-37 (terminal No.1)
- SRS-ECU connector C-36 (terminal No.58) and the seat belt buckle switch (passenger's side) connector D-37 (terminal No.2)

Q. Is the check result normal?

YES go to Step 6.

NO Repair harness wires between SRS-ECU connector C-36 and the seat belt buckle switch
(passenger's side) connector D-37.

STEP 6. Seat belt buckle switch check (passenger's side).

Testing and Inspection

Q. Is the check result normal?

YES Go to Step 7.
NO Replace the seat belt buckle switch (passenger's side).
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.

Q. Is DTC B1B54, B1B55 or B1B56 set?

YES Replace the SRS-ECU (Refer to Service and Repair).
NO The procedure is complete.