INSPECTION PROCEDURE 1: Malfunction of the heater controller assembly (A/C-ECU) Power Supply System: Diagnosis

Required Special Tool: 

• MB991223: Test Harness Set

1. STEP 1. 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 2.
   • NO:  Repair or replace the connector. Refer to HARNESS CONNECTOR INSPECTION . Check that the A/C works normally.
2. STEP 2. Measure the voltage at heater controller assembly (A/C-ECU) connector C-147  .
   1. Disconnect heater controller assembly (A/C-ECU) connector C-147 and measure the voltage at the harness side.
   2. Turn the ignition switch to the "ON" position.
   3. Measure the voltage between terminal 20 and ground.
      • The measured value should be approximately 12 volts (battery positive voltage).

   Q: Is the measured voltage approximately 12 volts? 

   • YES:  Go to  Step 5.
   • NO:  Go to Step 3.
     Fig 1: Measuring Voltage Between Terminal 20 And Ground

     Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
3. STEP 3. Check ETACS-ECU connector C-317 for loose, corroded or damaged terminals, or terminals pushed back in the connector  .

   Q: Is ETACS-ECU connector C-317 in good condition? 

   • YES:  Go to Step 4.
   • NO:  Repair or replace the connector. Refer to HARNESS CONNECTOR INSPECTION . Check that the A/C works normally.
4. STEP 4. Check the wiring harness between heater controller assembly (A/C-ECU) connector C-147 (terminal 20) and ETACS-ECU connector C-317 (terminal 5)  .
   • Check the heater control unit power supply line for open circuit.
     NOTE: Also check joint connector C-03 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If joint connector C-03 is damaged, repair or replace the connector as described in Harness Connector Inspection, refer to HARNESS CONNECTOR INSPECTION .

   Q: Is the wiring harness between heater controller assembly (A/C-ECU) connector C-147 (terminal 20) and ETACS-ECU connector C-317 (terminal 5) 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. Check that the A/C works normally.
5. STEP 5. Measure the voltage at heater controller assembly (A/C-ECU) connector C-147  .
   1. Disconnect heater controller assembly (A/C-ECU) connector C-147 and measure the voltage at the harness side.
   2. Measure the voltage between terminal 10 and ground.
      • The measured value should be approximately 12 volts (battery positive voltage).

   Q: Is the measured voltage approximately 12 V? 

   • YES:  Go to  Step 7.
   • NO:  Go to Step 6.
     Fig 2: Measuring Voltage Between Terminal 10 And Ground

     Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
6. STEP 6. Check the wiring harness between heater controller assembly (A/C-ECU) connector C-147 (terminal 10) and the fusible link (36)  .
   NOTE: Also check ETACS-ECU connectors C-307 and C-317 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If ETACS-ECU connectors C-307 and C-317 is damaged, repair or replace the connector as described in Harness Connector Inspection, refer to HARNESS CONNECTOR INSPECTION .
   • Check the heater control unit power supply line for open circuit.

   Q: Is the wiring harness between heater controller assembly (A/C-ECU) connector C-147 (terminal 10) and the fusible link (36) 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. Check that the A/C works normally.
7. STEP 7. Measure the resistance at heater controller assembly (A/C-ECU) connector C-147  .
   1. Disconnect heater controller assembly (A/C-ECU) connector C-147, and measure at the wiring harness side.
   2. Measure the resistance between terminal 9 and ground.
      • The measured value should be 2 ohms or less.

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

   • YES:  Replace the heater control unit, and check that the A/C works normally.
   • NO:  Go to Step 8.
     Fig 3: Measuring Resistance Between Terminal 9 And Ground

     Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
8. STEP 8. Check the wiring harness between heater controller assembly (A/C-ECU) connector C-147 (terminal 9) and the ground  .
   • Check the heater controller assembly (A/C-ECU) ground line for open circuit.

   Q: Is the wiring harness between heater controller assembly (A/C-ECU) connector C-147 (terminal 9) 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. Check that the A/C works normally.