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:

CIRCUIT OPERATION
The A/C-ECU power system may be defective if the air conditioning, 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 Tools:
- MB991223: Harness Set
- MB992006: Extra Fine Probe

STEP 1. Measure the voltage at A/C-ECU connector C-26.




1. Disconnect A/C-ECU connector C-26 and measure the voltage at the harness side.
2. Turn the ignition switch to the "ON" position.




3. Measure the voltage between terminal 28 and ground.
- The measured value should be approximately 12 volts (battery positive voltage).

Q: Is the measured voltage approx. 12 volts?

YES: Go to Step 4.

NO: Go to Step 2.




STEP 2. Check A/C-ECU connector C-26 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is A/C-ECU connector C-26 in good condition?

YES: Go to Step 3.

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







STEP 3. Check the wiring harness between A/C-ECU connector C-26 (terminal 28) and the ignition switch (IG2).

NOTE: Also check junction block connectors C-203 and C-205 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If junction block connector C-203 or C-205 is damaged, repair or replace the connector as described in Harness Connector Inspection.

Q: Is the wiring harness between A/C-ECU connector C-26 (terminal 28) and the ignition switch (IG2) in good condition?

YES: It can be assumed that this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points- How to Cope with Intermittent Malfunctions.

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

STEP 4. Measure the resistance at A/C-ECU connector C-26.




1. Disconnect A/C-ECU connector C-26, and measure at the wiring harness side.




2. Measure the resistance between terminal 27 and ground.
- The measured value should be 2 ohms or less.

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

YES: Go to Step 7.

NO: Go to Step 5.




STEP 5. Check A/C-ECU connector C-26 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is A/C-ECU connector C-26 in good condition?

YES: Go to Step 6.

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




STEP 6. Check the wiring harness between A/C-ECU connector C-26 (terminal 27) and the ground.

Q: Is the wiring harness between A/C-ECU connector C-26 (terminal 27) and the ground in good condition?

YES: Replace the A/C-ECU.

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

STEP 7. Measure the voltage at A/C-ECU connector C-25.




1. Disconnect A/C-ECU connector C-25 and measure the voltage at the harness side.




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

Q: Is the measured voltage approximately 12 volts?

YES: Replace the A/C-ECU.

NO: Go to Step 8.




STEP 8. Check A/C-ECU connector C-25 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is A/C-ECU connector C-25 in good condition?

YES: Go to Step 9.

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







STEP 9. Check the wiring harness between A/C-ECU connector C-25 (terminal 3) and the battery.

NOTE: Also check joint connector C-02 and intermediate connector C-116 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If joint connector C-02 or intermediate connector C-116 is damaged, repair or replace the connector as described in Harness Connector Inspection.

Q: Is the wiring harness between A/C-ECU connector C-25 (terminal 3) and the battery in good condition?

YES: It can be assumed that this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points- How to Cope with Intermittent Malfunctions.

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