DTC B1857: Microphone Connection: Diagnosis

Required Special Tools 

• MB991223: Wiring harness set
• MB992006: Extra fine probe

1. STEP 1. Voltage measurement at the microphone unit connector (terminal No. 1). 
   1. Disconnect the microphone unit connector, and measure at the wiring harness side.
   2. Turn the ignition switch from OFF position to ON position.
   3. Check the voltage between the microphone unit connector (terminal No. 1) and body ground.

      OK: Approximately 5 volts 

      Q: Is the check result normal? 

      YES:  Go to Step  3.

      NO:  Go to Step  2.

2. STEP 2. Resistance measurement at the TCU connector (SNSI terminal). 
   1. Disconnect the TCU and the microphone unit connector, and measure at the wiring harness side.
   2. Check the resistance SNSI line between the TCU connector and the microphone unit connector.

      OK: The resistance should be 2 ohms or less 

      Q: Is the check result normal? 

      YES:  Go to Step  7.

      NO:  Repair the connector(s) or wiring harness.

3. STEP 3. Resistance measurement at the microphone unit connector (terminal No. 3). 
   1. Disconnect the microphone unit connector, and measure at the wiring harness side.
   2. Check the resistance between the microphone unit connector (terminal No. 3) and body ground.

      OK: The resistance should be 2 ohms or less 

      Q: Is the check result normal? 

      YES:  Replace the microphone unit.

      NO:  Go to Step  4.

4. STEP 4. Resistance measurement at the TCU connector (MI- terminal). 
   1. Disconnect the TCU and the microphone unit connector, and measure at the wiring harness side.
   2. Check the resistance between the TCU connector (MI- terminal) and microphone unit connector (terminal No. 1).

      OK: The resistance should be 2 ohms or less 

      Q: Is the check result normal? 

      YES:  Go to Step  5.

      NO:  Repair the connector(s) or wiring harness.

5. STEP 5. Resistance measurement at the TCU connector (MO- terminal). 
   1. Disconnect the TCU, and measure at the wiring harness side.
   2. Check the resistance between the TCU connector (MO- terminal) and body ground.

      OK: The resistance should be 2 ohms or less 

      Q: Is the check result normal? 

      YES:  Go to Step  7.

      NO:  Go to Step  6.

6. STEP 6. Resistance measurement at the TCU connector (MO- terminal). 
   1. Disconnect the TCU connector and the multivision display connector, and measure at the wiring harness side.
   2. Check the resistance between the TCU connector (MO- terminal) and the multivision display connector (MIC+ terminal).

      OK: The resistance should be 2 ohms or less 

      Q: Is the check result normal? 

      YES:  Replace the multivision display.

      NO:  Repair the connector(s) or wiring harness.

7. STEP 7. Using scan tool (M.U.T.-IIISE), check whether the DTC is set again. 

   Check again if the DTC is set in the TCU.

   CAUTION: To prevent damage to scan tool (M.U.T.-IIISE), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-IIISE).
   1. Connect scan tool (M.U.T.-IIISE). Refer to "HOW TO CONNECT THE SCAN TOOL (M.U.T.-IIISE) ."
   2. Erase the DTC.
   3. Turn the ignition switch from OFF position to ON position.
   4. Execute "Test" on the scan tool (M.U.T.-IIISE) special function.
      • Item No. 5: Microphone check (Door speaker)
   5. Check the DTC.

      Q: Is the DTC set? 

      YES:  Replace the TCU (Refer to TCU  ).

      NO:  The trouble can be an intermittent malfunction (Refer to How to use Troubleshooting/inspection Service Points - HOW TO COPE WITH INTERMITTENT MALFUNCTION ).