Code No.B1476: Power Supply Voltage (Ig1 (A) Voltage) Drops Abnormally. (Fuse No.2 Circuit)
Code No.B1477: Power Supply Voltage (Ig1 (B) Voltage) Drops Abnormally. (Fuse No.3 Circuit)












caution If diagnosis code B1476 Fuse No.2 or B1477 Fuse No.3 is set in the SRS-ECU always diagnose the CAN bus lines.

OPERATION



  • The SRS-ECU is powered from the ignition switch (IG1).
  • The SRS-ECU power is supplied from two circuits. Even if one circuit is shut off, the air bag can inflate.

DIAGNOSIS CODE SET CONDITIONS



PROBABLE CAUSES



  • Damaged wiring harnesses or connectors
  • Malfunction of the SRS-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnostics.
Use the M.U.T.-III to diagnose the CAN bus lines.

Q. Is the check result normal?
Go to Step 2.
Repair the CAN bus line (Refer to GROUP 54D, Diagnosis ).

STEP 2. Check whether the diagnosis code is reset.
Check again if the diagnosis code is set.
(1)Erase the diagnosis code.
(2)Ignition: "LOCK" (OFF) position to "ON"
(3)On completion, check that the diagnosis code is not reset.

Q. Is the diagnosis code set?
Go to Step 3.
There is an intermittent malfunction such as poor engaged connector(s) or open circuit (Refer to GROUP 00, How to Cope with Intermittent Malfunction ).

STEP 3. Check junction block fuse number 2 and 3.

Q. Is the fuse burned out?
Go to Step 6.
Go to Step 4.

STEP 4. Voltage measurement at the SRS-ECU connector D-24.
(1)Disconnect the negative battery terminal.
(2)Disconnect SRS-ECU connector D-24.
(3)Connect the negative battery terminal.
(4)Turn the ignition switch to the "ON" position.
(5)
caution Do not insert a test probe into the terminal from its front side directly as the connector contact pressure may be weakened.
Voltage measurement between D-24 harness side connector terminal 24 <B1476> or 23 <B1477> and body earth.
OK: 9 V or more.

Q. Is the check result normal?
Go to Step 8.
Go to Step 5.

STEP 5. Connector check: SRS-ECU connector D-24 and ignition switch (IG1), junction block connector D-405.


Q. Is the check result normal?
Check the harness wires for open circuit between SRS-ECU connector D-24 (terminal No.24 and 23) and ignition switch (IG1), and repair if necessary.
Replace it.

STEP 6. Check a burned-out fuse.
(1)Replace the fuse.
(2)Turn the ignition switch to the "ON" position, wait for at least one minute and then turn the ignition switch to the "LOCK" (OFF) position.
(3)Check the fuse.

Q. Is the fuse in good condition?
Go to Step 8.
Go to Step 7.

STEP 7. Resistance measurement at the junction block connector D-405.
(1)Disconnect SRS-ECU connector D-24.
(2)Disconnect junction block connector D-405, and measure at the wiring harness side.
(3)
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 terminal 25/7 and body earth.
OK: Open circuit

Q. Is the check result normal?
Check the other circuit which flows through fuse number 3.
Check the harness wire for short circuit between junction block connector D-405 (terminal No.25 or 7) and SRS-ECU connector D-24 (terminal No.24 or 23). Then go to Step 8, and repair if necessary.

STEP 8. Check whether the diagnosis code is reset.

Q. Is diagnosis code B1476 set?
Replace the SRS-ECU (Refer to ).
An intermittent malfunction is suspected (Refer to GROUP 00, How to Cope with Intermittent Malfunction ).