Inspection Procedure 1

INSPECTION PROCEDURE 1: Malfunction Of The Heater Control Unit Power Supply System. [Vehicles Without A/C]

Heater Control Unit Power Supply Circuit (Part 1):

Heater Control Unit Power Supply Circuit (Part 2):

TECHNICAL DESCRIPTION (COMMENT)
The heater control module 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 heater control module
- Damaged harness wires or connectors

DIAGNOSIS

Required Special Tool:
- MB991223: Test Harness Set

STEP 1. Check heater control module connector C-53 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is heater control module connector C-53 in good condition?

YES : Go to Step 2.

NO : Repair or replace the connector. Check that the A/C works normally.

STEP 2. Measure the voltage at heater control module connector C-53.

1. Disconnect heater control module connector C-53 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?

YES : Go to Step 5.

NO : Go to Step 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. Check that the A/C works normally.

STEP 4. Check the wiring harness between heater control module connector C-53 (terminal 15) and ETACS-ECU connector C-317 (terminal 5).

- Check the heater control module power supply line for open circuit.

Q: Is the wiring harness between heater control module connector C-53 (terminal 15) and ETACS-ECU connector C-317 (terminal 5) in good condition?

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

NO : Repair the wiring harness. Check that the A/C works normally.

STEP 5. Measure the voltage at heater control module connector C-53.

1. Disconnect heater control module connector C-53 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?

YES : Go to Step 7.

NO : Go to Step 6.

STEP 6. Check the wiring harness between heater control module connector C-53 (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.

- Check the heater control module power supply line for open circuit.

Q: Is the wiring harness between heater control module connector C-53 (terminal 13) and the fusible link (36) in good condition?

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

NO : Repair the wiring harness. Check that the A/C works normally.

STEP 7. Measure the resistance at heater control module connector C-53.

1. Disconnect heater control module connector C-53, 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?

YES : Replace the heater control module, and check that the A/C works normally.

NO : Go to Step 8.

STEP 8. Check the wiring harness between heater control module connector C-53 (terminal 14) and the ground.

- Check the heater control module ground line for open circuit.

Q: Is the wiring harness between heater control module connector C-53 (terminal 14) and ground in good condition?

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

NO : Repair the wiring harness. Check that the A/C works normally.