Inspection Procedure 2

Inspection procedure 2: Power supply circuit system













CIRCUIT OPERATION

To SRS-ECU, the power is supplied from two independent circuits (fuse No. 12 and 18) via IG1 relay of ETACS-ECU.
If the power is not supplied to SRS-ECU, the communication between scan tool (M.U.T.-III Sub Assembly) and SRS-ECU cannot be established.

TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THIS CASE:)

- Damaged wiring harness or connector
- Charging system failed
- Malfunction of the SRS-ECU
- Malfunction of the ETACS-ECU

DIAGNOSIS

Required Special Tools:

- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)

STEP 1. Power supply fuse check.

Q. Is the fuse in good condition?

YES Go to Step 3.
NO Go to Step 2
STEP 2. Check for a blown fuse.

(1)Replace the fuse.

(2)Turn the ignition switch to the "ON" position, wait for at least one minute and then turn the switch off.

(3)Check the fuse.

Q. Is the fuse in good condition?

YES Go to Step 3.
NO Repair the wiring harness between the C-313 ETACS-ECU connector terminal No. 4/2 and the C-36 SRS-ECU connector terminal No. 61/62, and replace the power supply fuse.
STEP 3. Resistance measurement at the C-37 SRS-ECU connectors





(1)While pushing the part "A" indicated in the figure of the harness side connector, turn the lock lever to the direction of the arrow to release the lock lever, and disconnect the C-37 SRS-ECU connectors.





(2)Take the measurements below at the C-37 wiring harness side connector.

- Continuity between C-37 wiring harness side connector terminal No. 17 and body ground
OK: Continuity (Less than 2 ohms)

Q. Is the check result normal?

YES Go to Step 4.

NO Repair the wiring harness between the C-37 SRS-ECU connector terminal No. 17 and the ground.

STEP 4. Measure the voltage at the C-36 SRS-ECU connector.

(1)Disconnect the negative battery terminal.





(2)While pushing the part "A" indicated in the figure of the harness side connector, turn the lock lever to the direction of the arrow to release the lock lever, and disconnect the C-36 SRS-ECU connector.
(3)Connect the negative battery terminal.
(4)Ignition switch: ON





(5)Take the measurements below at the C-36 harness side connector.

- Voltage between terminal No. 61, 62 and body ground
OK: 9 V or more

Q. Is the measured voltage within the specified range?

YES Go to Step 6.

NO Go to Step 5.

STEP 5. Check the harness for open circuit between SRS-ECU connector C-36 (terminal No.61 and 62) and the ETACS-ECU connector C-313 (terminal No.4 and 2).

(1)Disconnect the negative battery terminal.





(2)While pushing the part "A" indicated in the figure of the harness side connector, turn the lock lever to the direction of the arrow to release the lock lever, and disconnect the C-36 SRS-ECU connector.
(3)Disconnect the ETACS-ECU connector C-313.





(4)Check for continuity between the following terminals. It should be less than 2 ohms.
[Fuse No.12]

- SRS-ECU connector C-36 (terminal No.62) and the ETACS-ECU connector C-313 (terminal No.2)
[Fuse No.18]

- SRS-ECU connector C-36 (terminal No.61) and the ETACS-ECU connector C-313 (terminal No.4)

Q. Does continuity exist?

YES Replace the ETACS-ECU Electronic Time and Alarm Control System (ETACS)-ECU Removal and Installation).

NO Repair the harness wire between SRS-ECU connector C-36 and the ETACS-ECU connector C-313.

STEP 6. Retest the system

Q. Is the communication between scan tool and SRS-ECU possible?

YES Intermittent malfunction How to Cope With Intermittent Malfunctions.)
NO Replace SRS-ECU (Refer to Service and Repair).