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

WARNING: This page is about a different car, the 2015 Mitsubishi Lancer. However, it is still accessible from the selected car via links, so may be relevant.

Required Special Tool:

MB991223: Test Harness Set

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.
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.
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.
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 .
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.
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.
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 .
- 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.
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.
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.