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Inspection Procedure 2: Power supply circuit system
 
 
 
 
CIRCUIT OPERATION
To SRS-ECU, the power is supplied from two independent circuits (fuse No. 15 and 21) via ignition switch (IG1) <vehicles without keyless operation system> or IG1 relay <vehicles with keyless operation system>.
If the power is not supplied to SRS-ECU, the communication between scan tool MB991958 and SRS-ECU cannot be established.
 
 
 
TROUBLESHOOTING HINTS
  • Damaged wiring harness and connectors
  • Battery failure
  • Malfunction of the charging system
  • Malfunction of SRS-ECU
 
 
 
DIAGNOSIS
STEP 1. Fuse Nos. 15, 21 check.
Is the fuse in good condition?
Go to Step 3.
Go to Step 2.
 
STEP 2. Fuse open circuit check
(1) Replace the fuse.
(2) Turn the ignition switch to the "ON" position, wait for at least one minute, and then turn the switch "LOCK" (OFF).
(3) Check the fuse.
Is the fuse in good condition?
Go to Step 3.
Repair the wiring harness IG1A line between the junction block connector and SRS-ECU connector, IG1B line between the junction block connector terminal No. 8 and the SRS-ECU connector, and replace the fuse.
 
STEP 3. Check of open circuit in GND1 line between SRS-ECU and body ground.
Is the check result normal?
Go to Step 4.
The wiring harness may be damaged or the connector(s) may have loose, corroded or damaged terminals, or terminals pushed back in the connector. Repair the wiring harness as necessary.
 
STEP 4. Check of short to power supply, short to ground, and open circuit in IG1A, IG1B line between SRS-ECU and junction block.
Is the check result normal?
Go to Step 5.
The wiring harness may be damaged or the connector(s) may have loose, corroded or damaged terminals, or terminals pushed back in the connector. Repair the wiring harness as necessary.
 
STEP 5. Trouble symptom check.
Is the communication between scan tool and SRS-ECU possible?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
Replace SRS-ECU (Refer to ).