Code No.27: Driver’s seat belt pre-tensioner (squib) system (open-circuited in 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 driver’s seat belt pre-tensioner squib 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 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 27 set?

Go to Step 2.

Go to Step 3.

STEP 2. Resistance measurement between SRS-ECU connector C-147 (terminal No.5 and 6) and the harness side connector D-32 (terminal No.1 and 2).
(1)Disconnect the negative battery terminal.

(2)Disconnect SRS-ECU connector C-147.

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

(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-147 terminal No.5 and harness side connector C-148 terminal No.2
  • SRS-ECU connector C-147 terminal No.6 and harness side connector C-148 terminal No.1
OK: Less than 2 Ω

Q. Are the check results normal?

Go to Step 4.

Repair the harness wires between SRS-ECU connector C-147 (terminal No.5 and 6) and harness side connector C-148 (terminal No.1 and 2).

STEP 3. Resistance measurement between harness side connector C-148 (terminal No.1 and 2) and the driver’s seat belt pre-tensioner D-32 (terminal No.1 and 2).
(1)Disconnect the negative battery terminal.

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


(3)Driver’s seat belt pre-tensioner connector D-32, and measure at the wiring harness side. For connector D-32, use a flat-tipped screwdriver to pull out the locking button at the harness side connector, and then disconnect the connector.

(4)Connect D-32 harness side connector to special tool resistor harness (MB991884).

(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 the following terminals.

  • pre-tensioner side connector C-148 terminal No.1 and special tool terminal No.2
  • pre-tensioner side connector C-148 terminal No.2 and special tool terminal No.1
OK: Less than 2 Ω

Q. Are the check results normal?

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

Repair the harness wires between pre-tensioner side connector (terminal No.1 and 2) and driver’s seat belt pre-tensioner connector D-32 (terminal No.1 and 2).

STEP 4. Check whether the diagnosis code is reset.

Q. Is diagnosis code No.27 set?
Replace the SRS-ECU (Refer to).
An intermittent malfunction is suspected (Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points ).