Code No.28: Passenger’s (front) seat belt pre-tensioner (squib) system (short-circuit between terminals of the squib 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 outputs an ignition signal. At this time, if the front air bag safing G-sensor is on, the pre-tensioner will deploy.

DIAGNOSIS CODE SET CONDITIONS


This diagnosis code is set if one Passenger’s pre-tensioner squib wire shorted to the other. However, if no diagnosis code resets, the SRS warning lamp will be switched off (diagnosis code will be retained).

PROBABLE CAUSES



note *: The squib circuit connectors integrate a "short" spring (which prevents the air bag from deploying unintentionally due to static electricity by shorting the positive wire to the earth wire in the squib circuit when the connectors are disconnected). Therefore, if connector C-147, C-148 or D-19 is damaged or improperly engaged, the short spring may not be released when the connector is connected.

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III diagnosis code

Q. Is diagnosis code 34 set?
Go to Step 2.
Go to Step 3.

STEP 2. Connector lock check: SRS-ECU connector C-147 (M.U.T.-III diagnosis code).
(1)Disconnect the negative battery terminal.

(2)Disconnect the connectors C-147 and then reconnect them.
(3)Connector the negative battery terminal.
(4)Erase the diagnosis code memory, and check the diagnosis code.

Q. Is diagnosis code 28 set?

Go to Step 3.

The procedure is complete. It is assumed that diagnosis code 28 set as connector C-147 was engaged improperly.

STEP 3. Connector lock check: SRS-ECU connector C-147 and Passenger’s seat belt pre-tensioner connector D-19 (M.U.T.-III diagnosis code).
(1)Disconnect the negative battery terminal.




(2)Disconnect connectors C-147, C-148 or D-19, and then reconnect them. For connector D-19, use a flat-tipped screwdriver to pull out the locking button at the harness side connector, and then disconnect the connector.
(3)Connector the negative battery terminal.
(4)Erase the diagnosis code memory, and check the diagnosis code.

Q. Is diagnosis code 28 set?

Go to Step 4.

The procedure is complete. It is assumed that diagnosis code 28 set as connector C-147, C-148, or D-19 was engaged improperly.

STEP 4. Check the diagnosis code by connecting a dummy resistor (M.U.T.-III diagnosis code).
(1)Disconnect the negative battery terminal.

(2)Disconnect intermediate connector C-148 (pre-tensioner harness and instrument panel harness connection).

(3)Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991866).
(4)
caution Do not insert a test probe into the terminal from its front side directly as the connector contact pressure may be weakened.
Connect special tool (MB991866) to the C-148 harness side connector by backprobing.
(5)Connect the negative battery terminal.
(6)Erase diagnosis code memory, and then check the diagnosis code.

Q. Is diagnosis code 28 set?

Go to Step 5.

Go to Step 6.

STEP 5. Resistance measurement at the SRS-ECU connector C-147.
(1)Disconnect the negative battery terminal.


(2)Disconnect SRS-ECU connector C-147.
danger To prevents the air bag from deploying unintentionally, disconnect the driver’s seat belt pre-tensioner connector C-148 to short the squib circuit.
(3)Disconnect intermediate connector C-148 (pre-tensioner harness and instrument panel harness connection).

(4)
caution Insert an insulator such as a cable tie to a depth of 4mm or more, otherwise the short bar will not be released.
Insert a cable tie [3 mm wide, 0.5 mm thick] between terminals 7, 8 and the short bar to release the short spring.

(5)
caution Do not insert a test probe into the terminal from its front side directly as the connector contact pressure may be weakened.
Resistance measurement between C-147 harness side connector terminals 7 and 8.
OK: Open circuit

Q. Is the check result normal?

Go to Step 7.

Repair the harness wires between SRS-ECU connector C-147 (terminal No.5 and 6) and harness side connector D-19 (terminal No.1 and 2).

STEP 6. Resistance measurement at intermediate connector C-148.
(1)Disconnect the negative battery terminal.

(2)
danger To prevents the air bag from deploying unintentionally, disconnect the Passenger’s seat belt pre-tensioner connector D-19 to short the squib circuit.
(3)Disconnect Passenger’s seat belt pre-tensioner connector D-19. Use a flat-tipped screwdriver to pull out the locking button at the harness side connector, and then disconnect the connector.

(4)Disconnect intermediate connector C-148 (pre-tensioner harness and instrument panel harness connection).

(5)
caution Insert an insulator such as a cable tie to a depth of 4mm or more, otherwise the short bar will not be released.
Insert a cable tie [3 mm wide, 0.5 mm thick] between terminals 3, 4 and the short spring to release the short spring.

(6)
caution Do not insert a test probe into the terminal from its front side directly as the connector contact pressure may be weakened.
Resistance measurement between C-148 harness side connector terminals 3 and 4.
OK: Open circuit

Q. Is the check result normal?

Replace the passenger’s seat belt pre-tensioner (Refer to).

Repair the harness wires between Passenger’s seat belt pre-tensioner connector D-19 (terminal No.1 and 2) and pre-tensioner harness connector C-148 (terminal No.3 and 4).

STEP 7. Check whether the diagnosis code is reset.

Q. Is diagnosis code 26 set?
Replace the SRS-ECU (Refer to).
An intermittent malfunction is suspected (Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points ).