Inspection Procedure 25: Blower Fan Signal System <Manual A/C>


OPERATION

  • The air volume stage 3 terminal in the blower switch connector sends voltage signal according to the blower switch position (OFF, 1, 2, 3 or 4) to the engine-ECU connector terminal "BFAN".

FUNCTION

  • The engine-ECU adjusts the alternator generating voltage according to the blower switch position.

  • The engine-ECU uses the blower switch position signal to stop and restart the engine, based on the AS&G system principle.

PROBABLE CAUSES

  • Failed blower fan switch
  • Open/short circuit or harness damage in blower fan circuit or loose connector contact
  • Open/short circuit or harness damage in blower fan switch position signal circuit or loose connector contact
  • Failed engine-ECU

PROBABLE CAUSES

STEP 1. M.U.T.-III data list

  • Data list reference table (Refer to ).

    1. Item 176: Blower fan signal

Q. Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
Go to Step 2.

STEP 2. Perform voltage measurement at engine-ECU

  • Measure engine-ECU connector terminal voltage.
  • Ignition switch: ON
  • Voltage between terminal BFAN line and earth.
OK:
    System voltage (Blower switch position: OFF)
    3 - 9 V (Blower switch position: 1 or 2)
    1 V or less (Blower switch position: 3 or 4)

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

STEP 3. Check of open circuit, short circuit, and damage in BFAN line between engine-ECU connector and blower fan switch connector.

Q. Is the check result normal?
Go to Step 4.
Repair the connector(s) or wiring harness.

STEP 4. Perform the functional check of the blower fan.

  • The blower fan speed should correspond to the blower fan switch position.

Q. Is the check result normal?
Go to Step 5.
Check the blower fan-related circuit (Refer to GROUP 55A - Troubleshooting - Trouble symptom Chart ).

STEP 5. M.U.T.-III data list

  • Data list reference table (Refer to ).

    1. Item 176: Blower fan signal

Q. Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
Replace the engine-ECU.