INSPECTION PROCEDURE K-2: The low-beam headlamps do not illuminate normally.


caution Whenever the ECU is replaced, ensure that the input and output signal circuits are normal.


COMMENTS ON TROUBLE SYMPTOM
If the low-beam headlamps do not illuminate, the headlamp switch input circuit or the front-ECU may be defective.

POSSIBLE CAUSES

  • Malfunction of the column switch
  • Malfunction of the front-ECU
  • Damaged harness wires and connectors

DIAGNOSIS PROCEDURE

Step 1. ECU check by using the SWS monitor.
Check that the power supply and earth lines to the column switch (column-ECU) and the front-ECU and the SWS communication lines are normal.

  • Ignition switch: OFF
ECUS TO BE CHECKED
  • COLUMN ECU
  • FRONT ECU
OK: "OK" are displayed for all the items

Q. Are the check result normal?
"OK" are displayed for all the items : Go to Step 2.
"NG" is displayed on the "COLUMN ECU" menu. : Refer to Inspection Procedure A-2 "Communication with the column switch (column-ECU) is not possible ."
"NG" is displayed on the "FRONT ECU" menu. : Refer to Inspection Procedure A-4 "Communication with the front-ECU is not possible ."

Step 2. Function diagnosis by using the SWS monitor.
Check the SWS communication signal, which are related to the low-beam headlamps.
<Selected item> LIGHTING - HEADLAMP LO
  • Ignition switch: ON
  • Lighting switch: HEAD
Item No.
 Item name
 Normal condition
Item 00
 HEADLAMP SW
 ON
Item 03
 PASSING SW
 OFF
Item 30
 IG SW(IG1)
 ON
Item 35
 HD AUTO-CUT
 OFF
Item 70
 FRONT ECU ACK
 NORMAL ACK
OK: Normal conditions are displayed for all the items

Q. Are the check result normal?
Normal conditions are displayed for all the items. : Go to Step 3.
Normal condition is not displayed for item No.00 or 03. : Refer to inspection procedure P-5 "Column switch (lighting and turn-signal lamp switch) signal is not received ."
Normal condition is not displayed for item No.30. : Refer to inspection procedure P-2 "The ignition switch (IG1) signal is not received ."
Normal condition is not displayed for item No.35. : Refer to Inspection Procedure K-5 "The headlamp automatic-shutdown function does not work normally ."
Normal condition is not displayed for item No.70. : Replace the front-ECU.

Step 3. Connector check: A-14X front-ECU connector.

Q. Is the check result normal?

Go to Step 4.

Repair the defective connector.

Step 4. Voltage measurement at the A-14X front-ECU connector.

(1)Remove the front-ECU, and measure at the relay box side.

(2)Voltage between A-14X front-ECU connector terminal Nos. 3, 4 and body earth
OK: System voltage

Q. Is the check result normal?

Go to Step 6.

Go to Step 5.

Step 5. Check the wiring harness between A-14X front-ECU connector terminal Nos. 3, 4 to the fusible link (26).


  • Check the power supply line for open circuit.

Q. Is the check result normal?

The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).

Repair the wiring harness.

Step 6. Retest the system.
Check that the low-beam headlamps illuminate normally.

Q. Is the check result normal?
The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).
Replace the front-ECU.