Inspection Procedure 1

INSPECTION PROCEDURE 1: Malfunction of the heater control unit Power Supply System. [Vehicles without A/C]














TECHNICAL DESCRIPTION (COMMENT)

The heater control unit 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 unit

- Damaged harness wires or connectors

DIAGNOSIS

Required Special Tool:

- MB991223: Test Harness Set

STEP 1. Check heater control unit connector C-48 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Is heater control unit connector C-48 in good condition?

YES Go to Step 2.
NO Repair or replace the connector. Harness Connector Inspection.
Check that the A/C works normally.
STEP 2. Measure the voltage at heater control unit connector C-48.

(1)Disconnect heater control unit connector C-48 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. Harness Connector Inspection.
Check that the A/C works normally.
STEP 4. Check the wiring harness between heater control unit connector C-48 (terminal 15) 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 Harness Connector Inspection.

Q. Is the wiring harness between heater control unit connector C-48 (terminal 15) and ETACS-ECU connector C-317 (terminal 5) in good condition?

YES It can be assumed that this malfunction is intermittent. 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 control unit connector C-48.

(1)Disconnect heater control unit connector C-48 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 unit connector C-48 (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 Harness Connector Inspection.

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

Q. Is the wiring harness between heater control unit connector C-48 (terminal 13) and the fusible link (36) in good condition?

YES It can be assumed that this malfunction is intermittent. 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 control unit connector C-48.

(1)Disconnect heater control unit connector C-48, 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 unit, and check that the A/C works normally.

NO Go to Step 8.

STEP 8. Check the wiring harness between heater control unit connector C-48 (terminal 14) and the ground.

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

Q. Is the wiring harness between heater control unit connector C-48 (terminal 14) and ground in good condition?

YES It can be assumed that this malfunction is intermittent. How to Cope With Intermittent Malfunctions.
NO Repair the wiring harness. Check that the A/C works normally.