Code No.B1604:
Seat belt pre-tensioner (driver’s side) (squib) system (open-circuited in the squib circuit)
OPERATION
Only when the frontal impact exceeding the threshold is simultaneously detected (turned
ON) by the front impact sensor as well as by the analog G-sensor and safing G-sensor in SRS-ECU,
the electric current is supplied from SRS-ECU to the seat belt pre-tensioner (squib).
TROUBLE JUDGEMENT
The code is set when the open circuit occurs to the SRS-ECU seat belt pre-tensioner (driver’s
side) (squib) circuit.
PROBABLE CAUSES
Open circuit to seat belt pre-tensioner (driver’s side) (squib)
circuit
Damaged wiring harness and connector
Malfunction of SRS-ECU
DIAGNOSIS PROCEDURE
STEP 1. Diagnosis check by dummy resistor connection.
(1)Check that the negative auxiliary battery terminal is disconnected. If the negative
auxiliary battery terminal is connected, disconnect it.
(2)Disconnect seat belt pre-tensioner (driver’s side) connector C-18 <LHD> or
C-31 <RHD>. Use a flat-tipped screwdriver to pull out the locking button at
the harness side connector, and then disconnect the connector.
(3)Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991884). (4)Connect special tool (MB991884) to the C-18 <LHD> or C-31 <RHD> harness
side connector. (5)Connect the negative auxiliary battery terminal. (6)After erasing the diagnosis code memory, check the diagnosis code again. (7)Disconnect the negative auxiliary battery terminal.
Q.
Is the diagnosis code No. B1604 set?
Go to Step 2
Replace the seat belt with pre-tensioner (driver’s side) (Refer to ).
STEP 2. Resistance measurement at the B-111 SRS-ECU connector and
the C-18 <LHD> or C-31 <RHD> seat belt pre-tensioner connector.
(1)Check that the negative auxiliary battery terminal is disconnected. If the negative
auxiliary battery terminal is connected, disconnect it.
(2)Disconnect the B-111 SRS-ECU connector.
(3)
danger
To prevents the seat belt pre-tensioner from operating
unintentionally, disconnect the seat belt pre-tensioner (driver’s side) connector to
short the squib circuit.
Disconnect seat belt pre-tensioner (driver’s side) connector C-18 <LHD> or
C-31 <RHD>. Use a flat-tipped screwdriver to pull out the locking button at
the harness side connector, and then disconnect the connector.
(4)
caution
The short spring may not be released due to the insufficient insertion. Therefore, insert
the insulator for 4 mm or more.
Insert an insulator (width: 3 mm, thickness: 0.5 mm) such as cable tie between the terminal
51/52 the short spring, and release the short spring.
(5)Connect special tool resistor harness (MB991884) to the removed C-18 <LHD> or
C-31 <RHD> harness side connector.
(6)
caution
Do not insert a test probe into the terminal from its front side directly as the connector
contact pressure may be weakened.
Take the measurements below at the resistor harness and B-111 harness side connector.
Continuity between B-111 SRS-ECU connector terminal No.
51 and resistor harness connector terminal No. 1
Continuity between B-111 SRS-ECU connector terminal No. 52 and resistor harness
connector terminal No. 2
OK: Continuity (less than 2 Ω)
Q.
Is the check result normal?
Go to Step 3
Repair the harness wires between SRS-ECU connector B-111 (terminal No.51 and 52)
and the seat belt pre-tensioner (driver’s side) connector C-18 <LHD> or
C-31 <RHD> (terminal No.2 and 1)
STEP 3. Check whether the diagnosis code is reset.
Q.
Is diagnosis code No.B1604 set?
Replace the SRS-ECU (Refer to ).
An intermittent malfunction is suspected (Refer to GROUP 00, How to Cope with
Intermittent Malfunction ).
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Go to Step 2
Replace the seat belt with pre-tensioner (driver’s side) (Refer to 
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