Inspection Procedure 1: Power supply to the BSW-ECU (master) fails [Cannot communicate with BSW-ECU (master) using the scan tool (M.U.T.-IIISE).]: Diagnosis

Required Special Tools: 

• MB991223: Harness Set
• MB992006: Extra Fine Probe

1. STEP 1. Resistance measurement at BSW-ECU (master) connector terminal GND. 
   1. Disconnect the connector, and measure at the wiring harness side.
   2. Measure the resistance between the BSW-ECU (master) connector terminal GND and body ground.

      OK: Is the measured resistance 2 ohms or less 

      Q: Is the check result normal? 

      YES:  Go to Step  2.

      NO:  Repair the ground line circuit {between the BSW-ECU (master) and body ground}.

2. STEP 2. Voltage measurement at BSW-ECU (master) connector terminal IG. 
   1. Disconnect the connector, and measure at the wiring harness side.
   2. Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.
   3. Check the voltage between the BSW-ECU (master) connector terminal IG and body ground.

      OK: Is the measured voltage approximately 12 volts (battery positive voltage) 

      Q: Is the check result normal? 

      YES:  Go to Step  3.

      NO:  Repair the power supply circuit {between the BSW-ECU (master) and ETACS-ECU}.

3. STEP 3. Retest the system. 

   Check if scan tool (M.U.T.-IIISE) can communicate with the BSW-ECU (master).

   Q: Is the check result normal? 

   YES:  Intermittent malfunction is suspected (Refer to How to use Troubleshooting/inspection Service Points - HOW TO COPE WITH INTERMITTENT MALFUNCTION ).

   NO:  Replace the BSW-ECU (master).