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

This diagnosis code is set if the voltage between the IG1 terminals (fuse No.21 circuit) and earth is lower than a predetermined value for a continuous period of 5 seconds or more.

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-131.

(1)Disconnect the negative battery terminal.

(2)Disconnect SRS-ECU connector C-131.
(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-131 harness side connector terminal 13 and body earth.
OK: 9 V or more

Q. Is the check result normal?

Erase the diagnosis code memory, and check the diagnosis code. If diagnosis code B1477 sets, replace the SRS-ECU (Refer to

). Then go to Step 7.

Go to Step 3.

STEP 3. Connector check: SRS-ECU connector C-131 and ignition switch connector C-307, 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-131 (terminal No.13) and ignition switch connector C-307 (terminal No.2), and repair if necessary. Then go to Step 7.

Repair or replace it. Then go to Step 7.

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?

	Go to Step 7.

	Go to Step 5.

STEP 5. Resistance measurement at the junction block connector C-208

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

(2)

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 8.

Go to Step 6.

STEP 6. Resistance measurement at the SRS-ECU connector C-131.

(1)Disconnect SRS-ECU connector C-131 and measure at the wiring harness side.

(2)

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 13 and body earth.
OK: Open circuit

Q. Is the check result normal?

Go to Step 7.

Check the harness wire for short circuit between SRS-ECU connector C-131 (terminal No.13) and junction block connector C-208 (terminal No.8), and repair if necessary.

STEP 7. 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 ).