Code No.4B: Curtain air bag module (squib) (LH) system (open-circuited in the squib circuit)




OPERATION


The SRS-ECU judges how severe a collision is by detecting signals from the side impact sensors and the side air bag safing G-sensor. If the impact is over a predetermined level, the SRS-ECU outputs an ignition signal. At this time, if the side air bag safing G-sensor is on, the curtain air bag module will deploy.

DIAGNOSIS CODE SET CONDITIONS


This diagnosis code is set if curtain air bag module squib <LH> wire(s) are open-circuited. However, if no diagnosis code resets, the SRS warning lamp will be switched off (diagnosis code will be retained).

PROBABLE CAUSES



DIAGNOSIS PROCEDURE

STEP 1. 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 G-22 (connection between curtain air bag harness and floor harness).

(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 G-22 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 4B set?

Go to Step 2.

Go to Step 3.

STEP 2. Resistance measurement between SRS-ECU connector C-146 (terminal No.27 and 28) and harness side connector G-22 (terminal No.1 and 2).
(1)Disconnect the negative battery terminal.

(2)Disconnect SRS-ECU connector C-146.

(3) Disconnect intermediate connector G-22 (connection between curtain air bag harness and floor harness).

(4)
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 the following terminals.

  • SRS-ECU connector C-146 terminal No.27 and harness side connector G-22 terminal No.1
  • SRS-ECU connector C-146 terminal No.28 and harness side connector G-22 terminal No.2
OK: Less than 2 Ω

Q. Are the check results normal?

Go to Step 4.

Repair the harness wire between SRS-ECU connector C-146 (terminal No.27 and 28) and harness side connector G-22 (terminal No.1and 2).

STEP 3. Resistance measurement between curtain air bag module (LH) side connector G-22 (terminal No.1 and 2) and the curtain air bag module G-01 (terminal No.1 and 2).

(1)Disconnect the negative battery terminal.

(2)Disconnect harness side connector G-22 and curtain air bag module connector G-01, and measure at the wiring harness side. For connector G-01, use a flat-tipped screwdriver to pull out the locking button at the harness side connector, and then disconnect the connector.

(3)Connect G-22 harness side connector to special tool resistor harness (MB991884).

(4)
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 the following terminals.

  • curtain air bag module (LH) side connector G-22 terminal No.1 and special tool terminal No.1
  • curtain air bag module (LH) side connector G-22 terminal No.2 and special tool terminal No.2
OK: Less than 2 Ω

Q. Are the check results normal?

Replace the curtain air bag module (Refer to).

Repair the harness wire between curtain air bag module (LH) side connector G-22 (terminal No.1 and 2) and curtain air bag module connector G-01 (terminal No.1and 2).

STEP 4. Check whether the diagnosis code is reset.

Q. Is diagnosis code No.4B set?
Replace the SRS-ECU (Refer to).
An intermittent malfunction is suspected (Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points ).