Rear Window Defogger Does not Operate

Rear window defogger does not operate.






























TECHNICAL DESCRIPTION (COMMENT)

The rear window defogger is able to turn on while engine is running. If the defogger does not operate when the rear window defogger switch is turned on, the rear window defogger relay system may be defective.

TROUBLESHOOTING HINTS

- The A/C-ECU[ vehicles with A/C] or heater control module[ vehicles without A/C] may be defective.
- The rear window defogger relay may be defective.
- The A/C control panel[ vehicles with A/C] or heater control panel[ vehicles without A/C] may be defective.
- The ETACS-ECU may be defective.
- Damaged harness wires or connectors

DIAGNOSIS

Required Special Tools:

- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)
- MB991223: Harness Set
- MB992006: Extra Fine Probe

STEP 1. Using scan tool MB991958, diagnose the CAN bus line.





(1)
CAUTION:
To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK"
(OFF) position before connecting or disconnecting scan tool MB991958.

Connect scan tool MB991958. Refer to "How to connect the Scan Tool (M.U.T.-III) Scan Tool Testing and Procedures."
(2)Turn the ignition switch to the "ON" position.
(3)Diagnose the CAN bus line.
(4)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the CAN bus line found to be normal?

YES Go to Step 2.

NO Repair the CAN bus line CAN Bus Diagnostics Chart).

STEP 2. Check the A/C and outside/inside air selection damper control motor operation.

(1)Turn the ignition switch to the "ON" position.

(2)Check the engine running.

(3)Check the operations of outside/inside air selection damper control motor and A/C.

Q. Do the A/C and outside/inside air selection damper control motor work normally?

YES Go to Step 3.
NO Inspection Procedure 2 [vehicles with A/C] or Inspection procedure 1, "Malfunction of the heater control unit power supply system Inspection Procedure 1 [vehicles without A/C]."
STEP 3. Using scan tool MB991958, read the A/C-ECU diagnostic trouble code.

Check that the A/C-ECU has not set a DTC.

Q. Is the DTC set?

YES Carry out the DTC procedures. Heating and Air Conditioning.
NO Go to Step 4.
STEP 4. Using scan tool MB991958, read the ETACS-ECU diagnostic trouble code.

Check that the ETACS-ECU has not set a DTC.

Q. Is the DTC set?

YES Carry out the DTC procedures. Refer to Electronic Time and Alarm Control System (ETACS).
NO Go to Step 5.
STEP 5. Using scan tool MB991958, check data list.

Use the A/C-ECU data list to check the signals related to the rear window defogger switch.

- Start the engine.
- Turn the rear window defogger switch from off to on.





Q. Does scan tool MB991958 display the items "ON", and "OFF" as normal condition?

YES Go to Step 6
NO : Replace the A/C control panel.
STEP 6. Check rear window defogger relay connector C-306 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Is rear window defogger relay connector C-306 in good condition?

YES Go to Step 7.
NO Repair or replace the connector. Harness Connector Inspection.
The rear window defogger system should work normally.
STEP 7. Check the rear window defogger relay continuity.

Follow the table below to check the rear window defogger relay for continuity.









Q. Is the rear window defogger relay in good condition?

YES Go to Step 8.

NO Replace the rear window defogger relay. The rear window defogger system should work normally.

STEP 8. Check rear window defogger connector F-29 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Are rear window defogger connector F-29 in good condition?

YES Go to Step 9.
NO Repair or replace the connector. Harness Connector Inspection.
The rear window defogger system should work normally.
STEP 9. Measure the voltage at rear window defogger connector F-29.

(1)Disconnect rear window defogger connector F-29, and measure the voltage at the harness side.

(2)Start the engine.

(3)Rear window defogger switch: ON (measure within 20 minutes after the switch is turned on)





(4)Measure the voltage between rear window defogger connector F-29 terminal No.1 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 10.

NO Go to Step 11.

STEP 10. Measure the resistance at rear window defogger connector F-03.

(1)Disconnect rear window defogger connector F-03, and measure at the wiring harness side.





(2)Measure the resistance between terminal 1 and ground.

- The measured value should be 2ohms or less.

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

YES Go to Step 19.

NO Repair the wiring harness. Check that the rear window defogger system works normally.

STEP 11. Measure the voltage at rear window defogger relay connector C-306.

(1)Disconnect rear window defogger relay connector C-306, and measure the voltage at the junction block side.





(2)Measure the voltage between terminal 4 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 13.

NO Go to Step 12.

STEP 12. Check the wiring harness between rear window defogger relay connector C-306 (terminal 4) and the fusible link (37).

NOTE:
Also check intermediate connector C-132 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If intermediate connector C-132 is damaged, repair or replace the connector as described in Harness Connector Inspection Harness Connector Inspection.

Q. Is the wiring harness between rear window defogger relay connector C-306 (terminal 4) and the fusible link (37) in good condition?

YES The trouble can be an intermittent malfunction How to Cope With Intermittent Malfunctions).
NO Repair the wiring harness. Check that the rear window defogger system works normally.
STEP 13. Measure the voltage at rear window defogger relay connector C-306.

(1)Disconnect rear window defogger relay connector C-306, and measure the voltage at the junction block side.

(2)Turn the ignition switch to the "ON" position.





(3)Measure the voltage between terminal 2 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 14.

NO Go to Step 16.

STEP 14. Check ETACS-ECU connector C-301 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Is ETACS-ECU connector C-301 in good condition?

YES Go to Step 15.
NO Repair or replace the connector. Harness Connector Inspection.
Check that the rear window defogger system works normally.
STEP 15. Check the wiring harness between rear window defogger relay connector C-306 (terminal 1) and ETACS-ECU C-301 (terminal 12).

Q. Is the wiring harness between rear window defogger relay connector C-306 (terminal 1) and ETACS-ECU connector C-301 (terminal 12) in good condition?

YES Go to Step 18
NO Repair the wiring harness. Check that the rear window defogger system works normally.
STEP 16. Check A/C control panel connector C-123 [vehicles with A/C] or heater control panel connector C-138 [vehicles without A/C] for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Are A/C control panel connector C-123[ vehicles with A/C] or heater control panel connector C-138[ vehicles without A/C] in good condition?

YES Go to Step 17.
NO Repair or replace the connector. Harness Connector Inspection.
The rear window defogger system should work normally.
STEP 17. Check the wiring harness between rear window defogger relay connector C-306 (terminal 2) and ETACS-ECU connector C-317 (terminal 5).

- Check the wiring harness for open circuit and short circuit.

NOTE:
Also check joint connector C-101 for loose, corroded, or damaged terminal, or terminal pushed back in the connector. If joint connector C-101 is damaged, repair or replace the connector as described in Harness Connector Inspection Harness Connector Inspection.

Q. Is the wiring harness between rear window defogger relay connector C-306 (terminal 2) and ETACS-ECU connector C-317 (terminal 5) in good condition?

YES The trouble can be an intermittent malfunction How to Cope With Intermittent Malfunctions).
NO Repair or replace the wiring harness. Harness Connector Inspection.
Check that the rear window defogger system works normally.
STEP 18. Check the wiring harness between rear window defogger relay connector C-306 (terminal 3) and rear window defogger connector F-29 (terminal 1).

NOTE:
Also check intermediate connectors C-42 and D-16 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If intermediate connectors C-42 and D-16 is damaged, repair or replace the connector as described in Harness Connector Inspection Harness Connector Inspection.

Q. Is the wiring harness between rear window defogger relay connector C-306 (terminal 3) and rear window defogger connector F-29 (terminal 1) in good condition?

YES Replace the ETACS-ECU.
NO Repair or replace the wiring harness. Harness Connector Inspection.
Check that the rear window defogger system works normally.
STEP 19. Check A/C-ECU [vehicles with A/C] connector C-22 or heater control module connector C-53 [vehicles without A/C] for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Is A/C-ECU[ vehicles with A/C] connector C-22 or heater control module connector C-53[ vehicles without A/C] in good condition?

YES Go to Step 20.
NO Repair or replace the connector. Harness Connector Inspection.
Check that the rear window defogger system works normally.
STEP 20. Check the wiring harness between A/C-ECU [vehicles with A/C] connector C-22 or heater control module connector C-53 [vehicles without A/C] (terminal 9) and A/C control panel connector C-123 [vehicles with A/C] or heater control panel connector C-138 [vehicles without A/C] (terminal 9).

- Check the wiring harness for open circuit and short circuit.

Q. Are the wiring harness between A/C-ECU[ vehicles with A/C] connector C-22 or heater control module connector C-53[ vehicles without A/C] (terminal 9) and A/C control panel connector C-123 (terminal 9) in good condition?

YES Go to Step 21.
NO Repair or replace the wiring harness. Harness Connector Inspection.
Check that the rear window defogger system works normally.
STEP 21. Check the rear window defogger.





(1)Let the engine run at 2,000 r/min, and check the printed heater with the battery fully charged.
(2)Turn on the rear window defogger switch, and use a voltmeter to measure the voltage in each printed heater at middle point A on the rear window glass.

- The value should be approximately 6 volts.

Q. Does the rear window defogger work normally?

YES Return to Step 1.

NO Replace the rear window defogger.