INSPECTION PROCEDURE 3: Blower air amount cannot be changed: Diagnosis

Required Special Tools: 

• MB991223: Harness Set
• MB992006: Extra Fine Probe

1. STEP 1. Check power transistor connector C-112 for loose, corroded or damaged terminals, or terminals pushed back in the connector  .

   Q: Is power transistor connector C-112 in good condition? 

   • YES:  Go to Step 2.
   • NO:  Repair or replace the connector. Refer to HARNESS CONNECTOR INSPECTION . The blower motor should operate normally.
2. STEP 2. Measure the resistance at power transistor connector C-112  .
   1. Disconnect power transistor connector C-112, 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.
     Fig 1: Measuring Resistance Value Between Terminal 1 And Ground

     Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
3. STEP 3. Check the wiring harness between power transistor connector C-112 (terminal 1) and ground  .
   • Check the power transistor ground line for open circuit.

   Q: Is the wiring harness between power transistor connector C-112 (terminal 1) and ground in good condition? 

   • YES:  It can be assumed that this malfunction is intermittent. Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTIONS .
   • NO:  Repair the wiring harness. The blower motor should operate normally.
4. STEP 4. Check the wiring harness between blower motor connector C-113 (terminal 2) and power transistor connector C-112 (terminal 2)  .
   • Check the heater control unit signal line for open and short circuit.

   Q: Is the wiring harness between blower motor connector C-113 (terminal 2) and power transistor connector C-112 (terminals 2) in good condition? 

   • YES:  Go to Step 5.
   • NO:  Repair the wiring harness. The blower motor should operate normally.
5. STEP 5. Check heater controller assembly (A/C-ECU) connector C-147 for loose, corroded or damaged terminals, or terminals pushed back in the connector  .

   Q: Is heater controller assembly (A/C-ECU) connector C-147 in good condition? 

   • YES:  Go to Step 6.
   • NO:  Repair or replace the connector. Refer to HARNESS CONNECTOR INSPECTION . The blower motor should operate normally.
6. STEP 6. Check the wiring harness between heater controller assembly (A/C-ECU) connector C-147 (terminal 15) and power transistor connector C-112 (terminal 4)  .
   • Check the heater control unit signal line for open and short circuit.

   Q: Is the wiring harness between heater control unit connector C-147 (terminal 15) and power transistor connector C-112 (terminal 4) in good condition? 

   • YES:  Go to Step 7.
   • NO:  Repair the wiring harness. The blower motor should operate normally.
7. STEP 7. 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 controller assembly (A/C-ECU).