INSPECTION PROCEDURE 12: 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 heater controller assembly (A/C-ECU)
  • Damaged wiring harness or connectors

DIAGNOSTIC PROCEDURE

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

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

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

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

STEP 3. Check of open circuit in heater controller assembly (A/C-ECU) IG1line between ETACS-ECU connector and heater controller assembly (A/C-ECU) 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 voltage at the heater controller assembly (A/C-ECU) connector.
(1)Disconnect the connector, and measure at the wiring harness side.
(2)Voltage between terminal No. 19 and body earth
OK: System voltage

Q. Is the check result normal?
Go to Step 6.
Go to Step 5.

STEP 5. Check of open circuit in heater controller assembly (A/C-ECU) B/UP line between ETACS-ECU connector and heater controller assembly (A/C-ECU) connector.
note Prior to the wiring harness inspection, check joint connector and repair if necessary.

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 6. Measure the resistance at the heater controller assembly (A/C-ECU) connector.
(1)Disconnect the connector, and measure at the wiring harness side.
(2)Resistance between terminal No. 18 and body earth
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?
Replace the heater controller assembly (A/C-ECU).
Go to Step 7.

STEP 7. Check of open circuit in heater controller assembly (A/C-ECU) E line between heater controller assembly (A/C-ECU) connector and earth J/C (DASH) 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.