B1476
DTC B1476: IG1 Power Supply Circuit System (Fuse No.3 Circuit)DTC B1477: IG1 Power Supply Circuit System (Fuse No.2 Circuit)
IG1 Power Supply Circuit:
CAUTION: If DTC B1476
CIRCUIT 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.
DTC SET CONDITIONS
This DTC is set if the voltage between the IG1 terminals (fuse No.3 circuit or fuse No.2 circuit) and ground is lower than a predetermined value for a continuous period of five second or more. However, if the vehicle condition returns to normal, DTC number B1476
TROUBLESHOOTING HINTS
- Damaged wiring harnesses or connectors
- Malfunction of the SRS-ECU
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A
STEP 1. Using scan tool MB991958, diagnose the CAN bus line.
CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
1. Connect scan tool MB991958. Refer to "How to connect the scan tool."
2. Turn the ignition switch to the "ON" position.
3. Diagnose the CAN bus line.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the CAN bus line found to be normal?
YES: Go to Step 2.
NO: Repair the CAN bus line (Refer to Information Bus, Diagnosis).
STEP 2. Recheck for diagnostic trouble code.
Check again if the DTC is set.
1. Erase the DTC.
2. Turn the ignition switch to "ON" position.
3. Check if the DTC is set.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the DTC set?
YES: Go to Step 3.
NO: There is an intermittent malfunction such as poor engaged connector(s) or open circuit (Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions).
STEP 3. Check junction block fuse number 3
Q: Is the fuse burned out?
YES: Go to Step 6.
NO: Go to Step 4.
STEP 4. Check the power supply circuit for open circuit. Measure the voltage at SRS-ECU connector C-123.
1. Disconnect the negative battery terminal.
2. Disconnect SRS-ECU connector C-123.
3. Connect the negative battery terminal.
4. Turn the ignition switch to the "ON" position.
CAUTION: Do not insert a test probe into the terminal from its front side directly, as the connector contact pressure may be weakened.
5. Measure the voltage between C-123 harness side connector terminal 23
Voltage should measure 9 volts or more.
Q: Is the measured voltage 9 volts or more?
YES: Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC B1476 or B1477 set, replace the SRS-ECU. Then go to Step 10.
NO: Go to Step 5.
STEP 5. Check the harness for open circuit between SRS-ECU connector C-123 (terminal No.23
NOTE: After inspecting intermediate connectors C-202 and C-215, inspect the wiring harness. If intermediate connectors are damaged, repair or replace them. Refer to Harness Connector Inspection. Then go to Step 10.
Q: Is the harness wire between SRS-ECU connector C-123 (terminal No.23
YES: Go to Step 10.
NO: Replace the harness wire between SRS-ECU connector C-123 and the ignition switch connector C-308. Then go to Step 10.
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?
YES: Go to Step 10.
NO: It is possible that the circuit using fuse No.3
STEP 7. Check the SRS-ECU power supply circuit for short circuit to ground. Measure the resistance at the junction block connector C-215.
1. Disconnect junction block connector C-215, and measure at the wiring harness side.
CAUTION: Do not insert a test probe into the terminal from its front side directly, as the connector contact pressure may be weakened.
2. Check for continuity between terminal 7
It should be open circuit.
Q: Does continuity exist?
YES: Check the other circuit, which flows through fuse No.3
NO: Go to Step 8.
STEP 8. Check the power supply circuit for short circuit to ground. Measure the resistance at the SRS-ECU connector C-123.
1. Disconnect SRS-ECU connector C-123, and measure at the wiring harness side.
CAUTION: Do not insert a test probe into the terminal from its front side directly as the connector contact pressure may be weakened.
2. Check for continuity between terminal 23
It should be open circuit.
Q: Does continuity exist?
YES: Go to Step 9.
NO: Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC B1476 or B1477 sets, replace the SRS-ECU. Then go to Step 10.
STEP 9. Check the harness for short circuit to ground between SRS-ECU connector C-123 (terminal No.23
Q: Is the harness wire between SRS-ECU connector C-123 (terminal No.23
YES: Go to Step 10.
NO: Replace the harness wire between SRS-ECU connector C-123 and junction block connector C-215. Then go to Step 10.
STEP 10. Recheck for diagnostic trouble code.
Check again if the DTC is set.
1. Erase the DTC.
2. Turn the ignition switch to the "ON" position.
3. Check if the DTC is set.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is DTC B1476 or DTC B1477 set?
YES: Return to Step 1.
NO: The procedure is complete.