B1C4A

DTC B1C4A: Front Passenger's Seat belt Pre-tensioner (Squib) System (Short Circuit between Squib Circuit Terminals)

CAUTION:
If DTC B1C4A is set 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 set if there is abnormal resistance between the input terminals of the passenger's seat belt pre-tensioner (squib).

TROUBLESHOOTING HITS

- Improper engaged connector or defective short spring*
- Short circuit between the passenger's seat belt pre-tensioner (squib) circuit terminals
- Damaged connector(s)
- Malfunction of the SRS-ECU

NOTE:
*: The squib circuit connectors integrate a "short" spring (which prevents the seat belt pre-tensioner from deploying unintentionally due to static electricity by shorting the positive wire to the ground wire in the squib circuit when the connectors are disconnected)
(Refer to Description and Operation). Therefore, if connector C-36 or D-40 is damaged or improperly engaged, the short spring may not be released when the connector is connected.

DIAGNOSIS

Required Special Tools:

- 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)
- MB991865: Dummy resistor
- MB991884: Resister harness

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 "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 SRS-ECU connector C-36 and passenger's seat belt pre-tensioner connector D-40.

(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. Then connect the connector.

(3)After disconnecting the D-40 harness side connectors, connect the connectors again. For the D-40 connector disconnection, 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)Connector the negative battery terminal.
(5)Erase the diagnostic trouble code memory, and check the diagnostic trouble code.

Q. Is DTC B1C4A set?

YES Go to Step 4.

NO The procedure is complete. It is assumed that DTC B1C4A set because connector C-36 or D-40 was engaged improperly.

STEP 4. Check the passenger's seat belt pre-tensioner.

(1)Disconnect the negative battery terminal.

(3)Disconnect passenger's seat belt pre-tensioner connector D-40. 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)Connect special tool MB991865 to special tool MB991884.
(5)Connect special tool MB991884 to the D-40 harness side connector.
(6)Connect the negative battery terminal.
(7)Erase diagnostic trouble code memory, and then check the diagnostic trouble code.

Q. Is DTC B1C4A set?

YES Go to Step 5.

NO Replace the passenger's seat belt with pre-tensioner (Refer to Seat Belts With Pre-Tensioner).
Then go to Step 7.

STEP 5. Check the passenger's seat belt pre-tensioner circuit.
Measure the resistance at the SRS-ECU connector C-36.

(1)Disconnect the negative battery terminal.

(3)DANGER:
To prevent the seat belt pre-tensioner from deploying unintentionally, disconnect the passenger's seat belt pre-tensioner connector D-40 to short the squib circuit.

Disconnect passenger's seat belt pre-tensioner connector D-40. 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)
CAUTION:
Insert 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 43, 44 and the short spring to release the short spring.

(5)Check for continuity between C-36 harness side connector terminals 43 and 44.
It should be an open circuit.

Q. Is it open circuit?

YES Erase the diagnostic trouble code memory, and check diagnostic trouble code. If DTC B1C4A set, replace the SRS-ECU (Refer to Service and Repair). Then go to Step 7 .

NO Go to Step 6.

STEP 6. Check the harness for short circuit between SRS-ECU connector C-36 (terminal No.43 and 44) and passenger's seat belt pre-tensioner connector D-40 (terminal No.2 and 1).

Q. Is the check result normal?

YES Go to Step 7.
NO Repair the harness wires between SRS-ECU connector C-36 and passenger's seat belt pre-tensioner connector D-40. Then go to Step 7.
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 B1C4A set?

YES Return to Step 1.
NO The procedure is complete.