Code No.B1477: Power supply voltage (IG1 (B) voltage) drops abnormally.




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. Check junction block fuse number 21.


Q. Is the fuse burned out?

Go to Step 4.

Go to Step 2.

STEP 2. Voltage measurement at SRS-ECU connector C-154.
(1)Disconnect the negative battery terminal.

(2)Disconnect SRS-ECU connector C-154.
(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 C-154 harness side connector terminal 43 and body earth.
OK: 9 V or more

Q. Is the check result normal?

Go to Step 6.

Go to Step 3.

STEP 3. Connector check: SRS-ECU connector C-154, junction block connector C-207 and C-208.



Q. Is the check result normal?

Check the harness wires for open or short circuit between SRS-ECU connector C-154 (terminal No.43) and ignition switch, and repair if necessary.

Replace it.

STEP 4. 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?
This diagnosis is complete.
Go to Step 5.

STEP 5. Resistance measurement at the junction block connector C-208
(1)Disconnect the negative battery terminal.

(2)Disconnect SRS-ECU connector C-154.


(3)Disconnect junction block connector C-208, and measure at the wiring harness side.

(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 terminal 8 and body earth.
OK: Open circuit

Q. Is the check result normal?

Check the other circuit, which flows through fuse number 21.

Repair the wiring harness between junction block connector C-208 (terminal No.8) and SRS-ECU connector C-154 (terminal No.43), and replace the fuse.

STEP 6. Check whether the diagnosis code is reset.

Q. Is diagnosis code B1477 set?
Replace the SRS-ECU (Refer to ).
An intermittent malfunction is suspected (Refer to GROUP 00, How to Cope with Intermittent Malfunction ).