B1546

DTC B1545: Occupant classification-ECU for Power Supply Circuit
DTC B1546: Occupant classification-ECU for Communication System

CAUTION:
If DTC B1545 or B1546 is set in the SRS-ECU, always diagnose the CAN main bus line.

CIRCUIT OPERATION

The load data from the occupant classification sensor is classified with the occupant classification-ECU, and its classified information is send to SRS-ECU. The SRS-ECU determines the air bag deployment based on this classified information, and controls the power supply circuit to the inflator.

DTC SET CONDITIONS

These DTCs are set if communication between the occupant classification-ECU and the SRS-ECU is not possible or communication is faulty.

TROUBLESHOOTING HINTS

- Damaged wiring harnesses or connectors
- Malfunction of the occupant classification-ECU
- Malfunction of the SRS-ECU

DIAGNOSIS

Required Special Tools:

- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A

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)Turn the ignition switch to the "ON" position.
(3)Diagnose the CAN bus line.
(4)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 the "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. Measure the resistance at occupant classification-ECU connector D-26.

(1)Disconnect the connector D-26.

(2)Check for continuity between D-26 harness side connector terminals 2 and body ground.
It should be 2 ohms or less.

Q. Is the measured resistance 2 ohms or less?

YES Then go to Step 4.

NO Repair the wiring harness between occupant classification-ECU connector D-26 terminals 2 and the body ground. Then go to Step 8.

STEP 4. Measure the voltage at occupant classification-ECU connector D-26.

(1)Disconnect the connector D-26.
(2)Turn the ignition switch to the "ON" position.

(3)Measure the voltage between terminal 2 and ground. It should measure approximately 12 volts (battery positive voltage).

Q. Is battery positive voltage (approximately 12 volts) present?

YES Go to Step 6.

NO Go to Step 5.

STEP 5. Check the harness wires for open circuit or short circuit between occupant classification-ECU connector D-26 (terminal No.2) and ignition switch (IG1).

NOTE:
After inspecting intermediate connectors C-23, C-202 and C-215 inspect the wiring harness. If intermediate connectors C-23, C-202 and C-215 are damaged, repair or replace them. Harness Connector Inspection. Then go to Step 8.

Q. Are the harness wires between occupant classification-ECU connector D-26 (terminal No.2) and ignition switch (IG1) in good condition?

YES Then go to Step 6.

NO Repair the harness wires between occupant classification-ECU connector D-26 and ignition switch connector. Then go to Step 8.

STEP 6. Check the harness wires for open circuit or short circuit between SRS-ECU connector C-124 (terminal No.66) and occupant classification-ECU connector D-26 (terminal No.3).

Q. Are the harness wires between SRS-ECU connector C-124 (terminal No.66) and occupant classification-ECU connector D-26 (terminal No.3) in good condition?

YES Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC B1545 or B1546 sets, replace the front seat slide adjuster Front Seat Assembly Removal and Installation). Then go to Step 7.

NO Repair the harness wires between SRS-ECU connector C-124 and occupant classification-ECU connector D-26. Then go to Step 8.

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 B1545 or B1546 set?

YES Replace the SRS-ECU (Refer to Service and Repair). Then go to Step 8.

NO The procedure is complete.

STEP 8. Recheck for diagnostic trouble code.