Inspection Procedure 2

INSPECTION PROCEDURE 2: Power Supply Circuit System













CIRCUIT OPERATION

- The SRS-ECU is energized by the ignition switch (IG1) through multi-purpose fuse 22 and the SRS-ECU terminal 23 and multi-purpose fuse 23 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-121.





(1)Disconnect the connector C-121.





(2)
CAUTION:
Do not insert a test probe into the terminal from its front side directly, as the connector contact pressure may be weakened.

Check for continuity between C-121 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-121 terminals 40 and the body ground. Then go to Step 5.

STEP 2. Check the harness wires for open circuit or short circuit to ground between SRS-ECU connector C-121 (terminal No.23 and 24) and ignition switch (IG1).









NOTE:
After inspecting intermediate connectors C-211 and C-215 inspect the wiring harness. If intermediate connectors C-211 and C-215 are damaged, repair or replace them. Harness Connector Inspection. Then go to Step 5.

Q. Are the harness wires between SRS-ECU connector C-121 (terminal No.23 and 24) and ignition switch (IG1) in good condition?

YES Go to Step 3.

NO Replace the harness wires between SRS-ECU connector C-121 and ignition switch
(IG1). Then go to Step 5.

STEP 3. Check the battery.

Check the battery 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 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 (M.U.T.-III Sub Assembly)?

YES It can be assumed that this malfunction is intermittent. How to Cope With Intermittent Malfunctions.

NO Replace the SRS-ECU (Refer to Service and Repair). Then go to Step 6.

STEP 6. Retest the system.





Q. Can the SRS-ECU communicate with the scan tool (M.U.T.-III Sub Assembly)?

YES The procedure is complete.

NO Go to Step 1.