INSPECTION PROCEDURE 2: Malfunction of the A/C-ECU Power Supply System: Diagnosis

WARNING: This page is about a different variant/trim than selected.

Required Special Tool:

MB991223: Test Harness Set

STEP 1. Check A/C-ECU connector C-22 for loose, corroded or damaged terminals, or terminals pushed back in the connector.
Q: Is A/C-ECU connector C-22 in good condition?
1. YES: Go to Step 2.
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 A/C-ECU connector C-22.
1. Disconnect A/C-ECU connector C-22 and measure the voltage at the harness side.
2. Turn the ignition switch to the "ON" position.
3. Measure the voltage between terminal 15 and ground.
  - The measured value should be approximately 12 volts (battery positive voltage).
  Q: Is the measured voltage approximately 12 volts?
  1. YES: Go to Step 5.
  2. NO: Go to Step 3.
    
    Fig 1: Measuring Voltage Between Terminal 15 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?
1. YES: Go to Step 4.
2. 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 A/C-ECU connector C-22 (terminal 15) and ETACS-ECU connector C-317 (terminal 5).
- Check the A/C-ECU power supply line for open circuit.
  Q: Is the wiring harness between A/C-ECU connector C-22 (terminal 15) and ETACS-ECU connector C-317 (terminal 5) in good condition?
  1. YES: It can be assumed that this malfunction is intermittent. Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTIONS .
  2. NO: Repair the wiring harness. Check that the A/C works normally.
STEP 5. Measure the voltage at A/C-ECU connector C-22.
1. Disconnect A/C-ECU connector C-22 and measure the voltage at the harness side.
2. Measure the voltage between terminal 13 and ground.
  - The measured value should be approximately 12 volts (battery positive voltage).
  Q: Is the measured voltage approximately 12 V?
  1. YES: Go to Step 7.
  2. NO: Go to Step 6.
    
    Fig 2: Measuring Voltage Between Terminal 13 And Ground
    Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
STEP 6. Check the wiring harness between A/C-ECU connector C-22 (terminal 13) 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 A/C-ECU power supply line for open circuit.
  Q: Is the wiring harness between A/C-ECU connector C-22 (terminal 13) and the FUSIBLE LINK (36) in good condition?
  1. YES: It can be assumed that this malfunction is intermittent. Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTIONS .
  2. NO: Repair the wiring harness. Check that the A/C works normally.
STEP 7. Measure the resistance at A/C-ECU connector C-22.
1. Disconnect A/C-ECU connector C-22, and measure at the wiring harness side.
2. Measure the resistance between terminal 14 and ground.
  - The measured value should be 2 ohms or less.
  Q: Does the measured resistance value correspond with this range?
  1. YES: Replace the A/C-ECU, and check that the A/C works normally.
  2. NO: Go to Step 8.
    
    Fig 3: Measuring Resistance Between Terminal 14 And Ground
    Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
STEP 8. Check the wiring harness between A/C-ECU connector C-22 (terminal 14) and the ground.
- Check the A/C-ECU ground line for open circuit.
  Q: Is the wiring harness between A/C-ECU connector C-22 (terminal 14) and ground in good condition?
  1. YES: It can be assumed that this malfunction is intermittent. Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTIONS .
  2. NO: Repair the wiring harness. Check that the A/C works normally.