INSPECTION PROCEDURE 4: The blower air volume cannot be changed


If air volume cannot be adjusted by using the blower control, the A/C control panel, the heater controller assembly (A/C-ECU) or the power transistor may be faulty.


  • Malfunction of the power transistor
  • Damaged wiring harness or connectors
  • Malfunction of the heater controller assembly (A/C-ECU)


STEP 1. M.U.T.-III CAN bus diagnostics

Use the M.U.T.-III to diagnose the CAN bus lines.

Q. Is the check result normal?

Go to Step 2.
Repair the CAN bus lines (Refer to GROUP 54C, Troubleshooting ).

STEP 2. M.U.T.-III diagnosis code

Check that the diagnosis code related to the air conditioner is not set.

Q. Is the diagnosis code set?

Carry out the diagnosis code procedures. Refer to .
Go to Step 3.

STEP 3. Resistance measurement at the power transistor connector.

(1)Disconnect the connector, and measure at the wiring harness side.
(2)Continuity between terminal 1 and body earth
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?

Go to Step 4.
Repair the wiring harness wires between power transistor connector terminal No. 1 and body earth.

STEP 4. Check of open circuit in P/TB, P/TC and E line between blower motor, power transistor, earth J/C(DASH) and heater controller assembly (A/C-ECU) connector.

Q. Is the check result normal?

Go to Step 5.
Repair the connector(s) or wiring harness.

STEP 5. Replace the power transistor and recheck the trouble symptom

Check that the blower motor operates normally.

Q. Is the check result normal?

This diagnosis is complete.
Replace the heater controller assembly (A/C-ECU).