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DTC B1612: Front Passenger's Seat belt Pre-tensioner (Squib) System (Shorted to Squib Circuit Power Supply)
 
 

cautionIf DTC B1612 is stored in the SRS-ECU, always diagnose the CAN main bus line.
 
 
CIRCUIT OPERATION
The SRS-ECU judges how severe a collision is by detecting signals from the front impact sensors and the front air bag analog G-sensor. If the impact is over a predetermined level, the SRS-ECU sends an ignition signal. At this time, if the front air bag safing G-sensor is on, the pre-tensioner will deploy.
 
 
DTC SET CONDITIONS
This DTC is stored if there is abnormal resistance between the input terminals of the passenger's seat belt pre-tensioner (squib).
 
 
TROUBLESHOOTING HITS
  • Damaged wiring harnesses or connectors
  • Short to the power supply in the passenger's seat belt pre-tensioner (squib) harness
  • 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) 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 stored.
(1) Erase the DTC.
(2) Turn the ignition switch to "ON" position.
(3) Check if the DTC is stored.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the DTC stored?
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 passenger's seat belt pre-tensioner.
(1) Disconnect the negative battery terminal.
(2) Disconnect passenger's seat belt pre-tensioner connector D-03. Use a flat-tipped screwdriver to unlock the locking button at the harness side connector by withdrawing it toward you in two stages, and then disconnect the connector.
(3) Connect special tool MB991865 to special tool MB991884.
(4) Connect special tool MB991884 to the D-03 harness side connector.
(5) Connect the negative battery terminal.
(6) Erase diagnostic trouble code memory, and then check the diagnostic trouble code.
Is DTC B1612 stored?
Go to Step 4.
Replace the passenger's seat belt with pre-tensioner (Refer to ). Then go to Step 6.
 
STEP 4. Check the passenger's seat belt pre-tensioner circuit. Measure the voltage at the SRS-ECU connector C-125.
(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)
dangerTo prevent the seat belt pre-tensioner from deploying unintentionally, disconnect the passenger’s seat belt pre-tensioner connector D-03 to short the squib circuit.
Disconnect passenger's seat belt pre-tensioner connector D-03. Use a flat-tipped screwdriver to unlock the locking button at the harness side connector by withdrawing it toward you in two stages, and then disconnect the connector.
(4)
cautionInsert an insulator such as a cable tie to a depth of 4mm (0.16 inch) or more, otherwise the short spring will not be released.
Insert a cable tie [3 mm (0.12 inch) wide, 0.5 mm (0.02 inch) thick] between terminals 31, 32 and the short spring to release the short spring.
(5) Connect the negative battery terminal.
(6) Ignition switch: "ON".

(7) Measure the voltage between C-125 harness side connector terminals 31, 32 and body ground.Voltage should measure 1 volt or less.
Is the measured voltage within the specified range?
Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC B1612 is stored, replace the SRS-ECU (Refer to ). Then go to Step 6.
Go to Step 5.
 
STEP 5. Check the harness wires for short circuit to power supply between SRS-ECU connector C-125 (terminal No.31 and 32) and passenger's seat belt pre-tensioner connector D-03 (terminal No.2 and 1).
Is the check result normal?
Go to Step 6.
Repair the harness wires between SRS-ECU connector C-125 and passenger's seat belt pre-tensioner connector D-03. Then go to Step 6.
 
STEP 6. Recheck for diagnostic trouble code.
Check again if the DTC is stored.
(1) Erase the DTC.
(2) Turn the ignition switch to the "ON" position.
(3) Check if the DTC is stored.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is DTC B1612 stored?
Return to Step 1.
The procedure is complete.