B1407

DTC B1407: Front Impact Sensor (RH) Power Supply Circuit System

Front Impact Sensor Circuit:

CAUTION: If DTC B1407 is set in the SRS-ECU, always diagnose the CAN main bus line.

CIRCUIT OPERATION
The front impact sensor includes an analog G-sensor and CPU, etc. The CPU monitors the analog G-sensor output signal. If the CPU judges that the front air bags should be deployed, it sends a fire signal to the SRS-ECU to deploy the front air bags. In addition, the CPU diagnoses the internal components of the front impact sensor. If a malfunction occurs, it requests the SRS-ECU to set a diagnostic trouble code.

DTC SET CONDITIONS
This DTC will set when the power supply voltage to the front impact sensor (RH) remains less than a predetermined value for five seconds. However, if the system returns to normal condition, code number B1407 will be erased automatically and the SRS warning light will go out.

TROUBLESHOOTING HINTS
- Damaged wiring harness or connectors
- Malfunction of the front impact sensor (RH)
- 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." How To Connect The Scan Tool (M.U.T.-III)
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.

STEP 2. 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 the DTC set?

YES : Go to Step 3.

NO : There is an intermittent malfunction such as poor engaged connector(s) or open circuit.

STEP 3. Check the front impact sensor (RH) power supply circuit. Measure the voltage at the front impact sensor (RH) connector A-27.

1. Connect the negative battery terminal.
2. 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.

3. Measure the voltage between A-27 harness side connector terminal 2 and ground.

A wave pattern of oscilloscope iterates an amplitude of 6 - 12 volts.

Q: Is the check result normal?

YES : Replace the front impact sensor (RH). Then go to Step 5.

NO : Go to Step 4.

STEP 4. Check the harness wires for open circuit or short circuit between SRS-ECU connector C-121 (terminal No.47 and 48) and front impact sensor (RH) connector A-27 (terminal No.2 and 1).

NOTE: After inspecting intermediate connector C-11 inspect the wiring harness. If the intermediate connector C-11 is damaged, repair or replace it.

Q: Are the harness wires between SRS-ECU connector C-121 (terminal No.47 and 48) and front impact sensor (RH) connector A-27 (terminal No.2 and 1) in good condition?

YES : Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC B1407 sets, replace the SRS-ECU. Then go to Step 5.

NO : Replace the harness wires between SRS-ECU connector C-121 and front impact sensor (RH) connector A-27. Then go to Step 5.

STEP 5. Recheck for diagnostic trouble code.