INSPECTION PROCEDURE 8: A/C-ECU power supply system


COMMENTS ON TROUBLE SYMPTOM
If the auto A/C 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 A/C-ECU.
  • Damaged wiring harness or connectors

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III other system’s diagnosis code
Check that the ETACS-ECU has not stored a diagnosis code.

Q. Is the diagnosis code stored?
Carry out the diagnosis code procedures. Refer to GROUP 54A, ETACS-ECU .
Go to Step 2.

STEP 2. Measure the voltage at the auto A/C controller assembly (A/C-ECU) connector.
(1)Disconnect the connector, and measure at the wiring harness side.
(2)Voltage between terminal No. 20 and body earth
OK: System voltage

Q. Is the check result normal?
Go to Step 3.
Go to Step 4.

STEP 3. Check open circuit in IG2 line between IG (2) relay and A/C controller assembly (A/C-ECU) connector.
note Before the wiring harness check, check the junction block connector.

Q. Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
Repair the connector(s) or wiring harness.

STEP 4. Measure the resistance at the auto A/C controller assembly (A/C-ECU) connector.
(1)Disconnect the connector, and measure at the wiring harness side.
(2)Resistance between terminal No. 19 and body earth
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?
Replace the auto A/C controller assembly (A/C-ECU).
Go to Step 5.

STEP 5. Check open circuit in E line between auto A/C controller assembly (A/C-ECU) connector and body earth.

Q. Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
Repair the wiring harness.