Inspection Procedure 3

INSPECTION PROCEDURE 3: Blower Air Amount Cannot Be Changed. [Vehicles Without A/C]

Blower Motor Circuit:

CIRCUIT OPERATION
If the blower motor speed cannot be changed, the power transistor circuit is suspected.

TROUBLESHOOTING HINTS
- Malfunction of the power transistor
- Malfunction of the heater control module
- Damaged harness wires or connectors

DIAGNOSIS

Required Special Tools:
- MB991223: Harness Set
- MB992006: Extra Fine Probe

STEP 1. Check power transistor connector C-119 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is power transistor connector C-119 in good condition?

YES : Go to Step 2.

NO : Repair or replace the connector. The blower motor should operate normally.

STEP 2. Measure the resistance at power transistor connector C-119.

1. Disconnect power transistor connector C-119, and measure the resistance at the wiring harness side.







2. Measure the resistance value between terminal 1 and ground.

OK: The measured value should be 2 ohms or less

Q: Does the measured resistance value correspond with this range?

YES : Go to Step 4.

NO : Go to Step 3.

STEP 3. Check the wiring harness between power transistor connector C-119 (terminal 1) and ground.

- Check the power transistor ground line for open circuit.

Q: Is the wiring harness between power transistor connector C-119 (terminal 1) and ground in good condition?

YES : It can be assumed that this malfunction is intermittent.

NO : Repair the wiring harness. The blower motor should operate normally.

STEP 4. Check heater control module connector C-53 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is heater control module connector C-53 in good condition?

YES : Go to Step 5.

NO : Repair or replace the connector. The blower motor should operate normally.

STEP 5. Check the wiring harness between heater control module connector C-53 (terminals 1 and 2) and power transistor connector C-119 (terminals 2 and 4).

- Check the heater control module signal line for open and short circuit.

Q: Is the wiring harness between heater control module connector C-53 (terminals 1 and 2) and power transistor connector C-119 (terminals 2 and 4) in good condition?

YES : Go to Step 6.

NO : Repair the wiring harness. The blower motor should operate normally.

STEP 6. Replace the power transistor and check the trouble symptom again

Check the trouble symptom again.

Q: Is the check result satisfactory?

YES : The procedure is complete.

NO : Replace the heater control module.