Inspection Procedure 10

INSPECTION PROCEDURE 10: Malfunction of the A/C-ECU Power Supply System.

A/C-ECU Power Supply Circuit (Part 1):

A/C-ECU Power Supply Circuit (Part 2):

TECHNICAL DESCRIPTION (COMMENT)
The A/C-ECU power system may be defective if the air conditioner, defogger, and outside/inside air selection damper motor all do not operate normally.

TROUBLESHOOTING HINTS
- Malfunction of the A/C-ECU
- Damaged harness wires or connectors

DIAGNOSIS

Required Special Tool:
- MB991223: Test Harness Set
- MB992006: Extra Fine Probe

STEP 1. Check A/C-ECU connector C-42 for loose, corroded or damaged terminals, or terminals pushed back in the connector.






Q: Is A/C-ECU connector C-42 in good condition?

YES : Go to Step 2.

NO : Repair or replace the connector. Check that the air conditioning works normally.

STEP 2. Measure the voltage at A/C-ECU connector C-42.






1. Disconnect A/C-ECU connector C-42 and measure the voltage at the harness side.
2. Turn the ignition switch to the "ON" position.






3. Measure the voltage between terminal 16 and ground.
- The measured value should be approximately 12 volts (battery positive voltage).

Q: Is the measured voltage approx. 12 V?

YES : Go to Step 4.

NO : Go to Step 3.

STEP 3. Check the wiring harness between A/C-ECU connector C-42 (terminal 16) and the ignition switch (IG2).












NOTE: Also check joint connector C-104, junction block connectors C-211 and C-215 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If joint connector C-104, junction block connector C-211 or C-215 is damaged, repair or replace the connector.
- Check the A/C-ECU power supply line for open circuit.

Q: Is the wiring harness between A/C-ECU connector C-42 (terminal 16) and the ignition switch (IG2) in good condition?

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

NO : Repair the wiring harness. Check that the air conditioning works normally.

STEP 4. Measure the voltage at A/C-ECU connector C-42.






1. Disconnect A/C-ECU connector C-42 and measure the voltage at the harness side.
2. Turn the ignition switch to the "ACC" position.






3. Measure the voltage between terminal 7 and ground.
- The measured value should be approximately 12 volts (battery positive voltage).

Q: Is the measured voltage approx. 12 V?

YES : Go to Step 6.

NO : Go to Step 5.

STEP 5. Check the wiring harness between A/C-ECU connector C-42 (terminal 7) and the ignition switch (ACC).









NOTE: Also check joint connector C-104 and intermediate connector C-31 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If joint connector C-104 or intermediate connector C-31 is damaged, repair or replace the connector.
- Check the A/C-ECU power supply line for open circuit.

Q: Is the wiring harness between A/C-ECU connector C-42 (terminal 7) and the ignition switch (ACC) in good condition?

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

NO : Repair the wiring harness. Check that the air conditioning works normally.

STEP 6. Measure the voltage at A/C-ECU connector C-42.






1. Disconnect A/C-ECU connector C-42 and measure the voltage at the harness side.






2. Measure the voltage between terminal 8 and ground.
- The measured value should be approximately 12 volts (battery positive voltage).

Q: Is the measured voltage approx. 12 V?

YES : Go to Step 8.

NO : Go to Step 7.

STEP 7. Check the wiring harness between A/C-ECU connector C-42 (terminal 8) and the battery.









NOTE: Also check joint connector C-04 and intermediate connector C-31 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If joint connector C-04 or intermediate connector C-31 is damaged, repair or replace the connector.
- Check the A/C-ECU power supply line for open circuit.

Q: Is the wiring harness between A/C-ECU connector C-42 (terminal 8) and the battery in good condition?

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

NO : Repair the wiring harness. Check that the air conditioning works normally.

STEP 8. Measure the resistance at A/C-ECU connector C-42.






1. Disconnect A/C-ECU connector C-42, and measure at the wiring harness side.






2. Measure the resistance between terminal 2 and ground.
- The measured value should be 2 ohms or less.

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

YES : Replace the A/C-ECU, and check that the air conditioning works normally.

NO : Go to Step 9.

STEP 9. Check the wiring harness between A/C-ECU connector C-42 (terminal 2) and the ground.









NOTE: Also check joint connector C-103 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If joint connector C-103 is damaged, repair or replace the connector.
- Check the A/C-ECU power supply line for open circuit.

Q: Is the wiring harness between A/C-ECU connector C-42 (terminal 2) and ground in good condition?

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

NO : Repair the wiring harness. Check that the air conditioning works normally.