Inspection Procedure 2: Power supply circuit system


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 M.U.T.-III and SRS-ECU cannot be established.

PROBABLE CAUSES

  • Damaged wiring harness and connectors
  • Battery failure
  • Malfunction of the charging system
  • Malfunction of SRS-ECU

DIAGNOSIS PROCEDURE

STEP 1. Fuse Nos. 12, 18 check.

Q. 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 OFF.
(3)Check the fuse.

Q. Is the fuse in good condition?
Go to Step 3.
Repair the wiring harness between the C-412 ETACS-ECU connector terminal No. 4 and C-126 SRS-ECU connector terminal No. 21, C-417 ETACS-ECU connector terminal No. 5 and the C-126 SRS-ECU connector terminal No. 22. and replace the fuse.

STEP 3. Resistance measurement at the C-126 SRS-ECU connector.

(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-126 SRS-ECU connectors.
(2)Take the measurements below at the C-126 wiring harness side connectors.

  • Continuity between C-126 wiring harness side connector terminal No. 24 and body earth
OK: Continuity (less than 2 Ω)

Q. Is the check result normal?

Go to Step 4.

Repair the wiring harness between the C-126 SRS-ECU connector terminal No. 24 and the earth.

STEP 4. Voltage measurement at the C-126 SRS-ECU connector.
(1)Check that the negative battery terminal is disconnected. If the negative battery terminal is connected, disconnect it.

(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-126 SRS-ECU connector.
(3)Connect the negative battery terminal.
(4)Ignition switch: ON
(5)Take the measurements below at the C-126 harness side connector.

  • Voltage between terminal No. 21/22 and body earth
OK: 9 V or more
(6)Disconnect the negative battery terminal.

Q. Is the check result normal?

Go to Step 6.

Go to Step 5.

STEP 5. Resistance measurement at the C-126 SRS-ECU connector.
(1)Check that the negative battery terminal is disconnected. If the negative battery terminal is connected, disconnect it.
(2)Disconnect the C-412 and C-417 ETACS-ECU connector.

(3)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-126 SRS-ECU connector.
(4)
  • Continuity between C-412 ETACS-ECU connector terminal No. 4 and C-126 SRS-ECU connector terminal No. 21
  • Continuity between C-417 ETACS-ECU connector terminal No. 5 and C-126 SRS-ECU connector terminal No. 22
OK: Continuity (less than 2 Ω)

Q. Is the check result normal?

Replace the ETACS-ECU (Refer to GROUP 54A - ETACS-ECU ).

Repair the wiring harness between the C-412 ETACS-ECU connector terminal No. 4 and the C-126 SRS-ECU connector terminal No. 21, C-417 ETACS-ECU connector terminal No. 5 and C-126 SRS-ECU connector terminal No. 22.

STEP 6. Trouble symptom check.

Q. Is the communication between M.U.T.-III 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 ).