Inspection Procedure 2
INSPECTION PROCEDURE 2: Power Supply Circuit SystemIG1 Power Supply Circuit:
CIRCUIT OPERATION
- The SRS-ECU is energized by the ignition switch (IG1) through multi-purpose fuse 3 and the SRS-ECU terminal 23 and multi-purpose fuse 2 and the SRS-ECU terminal 24.
- If the power supply to the SRS-ECU has failed, scan tool (M.U.T.-III Sub Assembly) will not be able to communicate with it.
TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THIS CASE:)
- Damaged wiring harness or connector
- Defective battery
- Charging system failed
- 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. Measure the resistance at SRS-ECU connector C-123.
1. Disconnect the connector C-123.
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 C-123 harness side connector terminals 40 and body ground.
It should be 2 ohms or less.
Q: Is the measured resistance 2 ohms or less?
YES: Then go to Step 2.
NO: Repair the wiring harness between SRS-ECU connector C-123 terminals 40 and the body ground. Then go to Step 5.
STEP 2. Check the harness wires for short circuit to ground between SRS-ECU connector C-123 (terminal No.23 and 24) and ignition switch connector C-308 (terminal No.2).
NOTE: After inspecting intermediate connectors C-202 and C-215 inspect the wiring harness. If intermediate connectors C-202 and C-215 are damaged, repair or replace them. Refer to Harness Connector Inspection. Connector Continuity and Voltage Test Then go to Step 5.
Q: Are the harness wires between SRS-ECU connector C-123 (terminal No.23 and 24) and ignition switch connector C-308 (terminal No.2) in good condition?
YES: Go to Step 3.
NO: Replace the harness wires between SRS-ECU connector C-123 and ignition switch connector C-308. Then go to Step 5.
STEP 3. Check the battery.
Check the battery (Refer to Battery test). Battery Test
Q: Is the battery in good condition?
YES: Go to Step 4.
NO: Charge or replace the battery. Then go to Step 5.
STEP 4. Check the charging system.
Check the charging system (Refer to Charging system diagnosis). Initial Inspection and Diagnostic Overview
Q: Is the charging system in good condition?
YES: Go to Step 5.
NO: Repair or replace the charging system component(s).Then go to Step 5.
STEP 5. Retest the system.
Q: Can the SRS-ECU communicate with the scan tool (MB991958)?
YES: It can be assumed that this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions.
NO: Replace the SRS-ECU. Then go to Step 6.
STEP 6. Retest the system.
Q: Can the SRS-ECU communicate with the scan tool (MB991958)?
YES: The procedure is complete.
NO: Go to Step 1.