INSPECTION PROCEDURE 11: Heater controller assembly (A/C-ECU) power supply system


COMMENTS ON TROUBLE SYMPTOM
If the heater controller assembly (A/C-ECU) is not energised, the power supply or earth system to the ECU may be defective.

PROBABLE CAUSES

  • Malfunction of the fuse
  • Malfunction of the fusible link
  • Malfunction of the IG1 relay
  • Malfunction of the heater controller assembly (A/C-ECU)
  • Damaged wiring harness or connectors

DIAGNOSIS PROCEDURE

STEP 1. Check the fuse (23), (26), (13).

Q. Is the fuse (23), (26), (13) in good condition?
Go to Step 3.
Go to Step 2.

STEP 2. Check of short circuit in B/UP line between fuse (23) and heater controller assembly (A/C-ECU) connector B/UP terminal.

Q. Is the check result normal?
Replace the fuse (23), (26), (13).
Repair or replace the connector(s) or wiring harness.

STEP 3. Check the fusible link (2).

Q. Is the fusible link (2) in good condition?
Go to Step 5.
Go to Step 4.

STEP 4. Check short circuit in fusible link line between fuse (23) and fusible link (2).

Q. Is the check result normal?
Replace the fusible link (2).
Repair or replace the connector(s) or wiring harness.

STEP 5. Check the fuse (15).

Q. Is the fuse (15) in good condition?
Go to Step 7.
Go to Step 6.

STEP 6. Check of short circuit in IG1 line between fuse (15) and heater controller assembly (A/C-ECU) connector IG1 terminal.

Q. Is the check result normal?
Replace the fuse (15).
Repair or replace the connector(s) or wiring harness.

STEP 7. Check the IG1 relay.

Q. Is the IG1 relay in good condition?
Go to Step 9.
Go to Step 8.

STEP 8. Check short circuit in fusible link line between fuse (15) and IG1 relay.

Q. Is the check result normal?
Replace the IG1 relay.
Repair or replace the connector(s) or wiring harness.

STEP 9. Resistance measurement at the heater controller (A/C-ECU) connector.
(1)Disconnect the connector, and measure at the wiring harness side.
(2)Continuity between terminal E and body earth
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?
Go to Step 11.
Go to Step 10.

STEP 10. Check of open circuit in E line between heater controller assembly (A/C-ECU) connector E terminal and body earth.

Q. Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).
Repair or replace the connector(s) or wiring harness.

STEP 11. Recheck the trouble symptom.

Q. Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).
Replace the heater controller assembly (A/C-ECU) (Refer to ).