Dtc B1291 Light System Communication Bus Malfunction (+B Short)

Communication System. Lexus Gs430, Gs300. Uzs190 Grs190
Multiplex Communication. Lexus Gs430, Gs300. Uzs190 Grs190

DESCRIPTION

WIRING DIAGRAM

INSPECTION PROCEDURE

CHECK DIAGNOSTIC TROUBLE CODE (A ECU)

CHECK DIAGNOSTIC TROUBLE CODE (B ECU)

CHECK WIRE HARNESS BETWEEN A ECU AND B ECU

CHECK DIAGNOSTIC TROUBLE CODE (C ECU)

CHECK WIRE HARNESS BETWEEN B ECU AND C ECU

CHECK WIRE HARNESS BETWEEN GATEWAY ECU AND A ECU OR C ECU

DTC B1291 Light System Communication Bus Malfunction (+B Short)

DTC B1292 Light System Communication Bus Malfunction (GND Short)


DESCRIPTION

When a +B or body ground short circuit is detected on the light system communication bus (BEAN), the light system communication bus (BEAN) is disabled and a DTC is output.

DTC No.
DTC Detection Condition
Trouble Area
B1291
Light system communication circuit and +B battery system short
  1. Network gateway ECU
  2. No. 1 junction block assembly (multiplex network rear ECU)
  3. Cowl side junction block ECU LH
  4. Position control ECU and switch assembly (driver side)
  5. Engine room No. 2 junction block
  6. AFS ECU
  7. Combination switch assembly (windshield wiper switch)
  8. Cowl side junction block RH
  9. Multiplex tilt and telescopic ECU
  10. Wire harness
B1292
Light system communication circuit and body ground short
  1. Network gateway ECU
  2. No. 1 junction block assembly (multiplex network rear ECU)
  3. Cowl side junction block ECU LH
  4. Position control ECU and switch assembly (driver side)
  5. Engine room No. 2 junction block
  6. AFS ECU
  7. Combination switch assembly (windshield wiper switch)
  8. Cowl side junction block RH
  9. Multiplex tilt and telescopic ECU
  10. Wire harness

WIRING DIAGRAM


Lexus Gs430, Gs300. Uzs190 Grs190.Multiplex Communication.Multiplex Communication System. Dtc B1291 Light System Communication Bus Malfunction (+B Short)


INSPECTION PROCEDURE

1.CHECK DIAGNOSTIC TROUBLE CODE (A ECU)

Lexus Gs430, Gs300. Uzs190 Grs190.Multiplex Communication.Multiplex Communication System. Dtc B1291 Light System Communication Bus Malfunction (+B Short)

  1. Disconnect the A ECU connector and check for DTCs B1291 and B1292.

    OK:
    DTCs B1291 and B1292 are not output.
    NOTICE:
    Reconnect the connector before starting the next check.
    HINT:
    1. The A ECU in the light system bus represents the No. 1 junction block assembly (multiplex network rear ECU).
    2. If the result is as specified, the disconnected A ECU No. 1 junction block assembly (multiplex network rear ECU) is malfunctioning.


B
REPLACE A ECU
A


2.CHECK DIAGNOSTIC TROUBLE CODE (B ECU)

Lexus Gs430, Gs300. Uzs190 Grs190.Multiplex Communication.Multiplex Communication System. Dtc B1291 Light System Communication Bus Malfunction (+B Short)

  1. Disconnect the A ECU and B ECU connectors and check for DTCs B1291 and B1292.

    OK:
    DTCs B1291 and B1292 are not output.
    NOTICE:
    Disconnect the connectors one by one. Reconnect the connectors before starting the next check.
    HINT:
    1. The B ECU in the door system bus represents one of the following: (cowl side junction block ECU LH, position control ECU and switch assembly (driver side), engine room No. 2 junction block, AFS ECU, combination switch assembly (windshield wiper switch).
    2. If the result is as specified, the disconnected B ECU (one of the ECUs listed above) or the wire harness between the A ECU and B ECU is malfunctioning.


B
Go to step 4
A


3.CHECK WIRE HARNESS BETWEEN A ECU AND B ECU

Lexus Gs430, Gs300. Uzs190 Grs190.Multiplex Communication.Multiplex Communication System. Dtc B1291 Light System Communication Bus Malfunction (+B Short)

  1. Disconnect the B ECU connector and check for DTCs B1291 and B1292.

    OK:
    DTCs B1291 and B1292 are not output.
    NOTICE:
    Reconnect the connector before starting the next check.
    HINT:
    If the result is as specified, the wire harness between the A ECU and B ECU is functioning normally but the disconnected B ECU is malfunctioning.


A
REPLACE B ECU

B
REPAIR OR REPLACE WIRE HARNESS BETWEEN A ECU AND B ECU

4.CHECK DIAGNOSTIC TROUBLE CODE (C ECU)

Lexus Gs430, Gs300. Uzs190 Grs190.Multiplex Communication.Multiplex Communication System. Dtc B1291 Light System Communication Bus Malfunction (+B Short)

  1. Disconnect the B ECU and C ECU connectors and check for DTCs B1291 and B1292.

    OK:
    DTCs B1291 and B1292 are not output.
    NOTICE:
    Disconnect the connectors one by one. Reconnect the connectors before starting the next check.
    HINT:
    1. The C ECU in the light system bus represents the cowl side junction block RH, multiplex tilt and telescopic ECU.
    2. If the result is as specified, the disconnected C ECU (cowl side junction block RH, multiplex tilt and telescopic ECU) or the wire harness between the B ECU and C ECU is malfunctioning.


B
Go to step 6
A


5.CHECK WIRE HARNESS BETWEEN B ECU AND C ECU

Lexus Gs430, Gs300. Uzs190 Grs190.Multiplex Communication.Multiplex Communication System. Dtc B1291 Light System Communication Bus Malfunction (+B Short)

  1. Disconnect the C ECU connector and check for DTCs B1291 and B1292.

    OK:
    DTCs B1291 and B1292 are not output.
    NOTICE:
    Reconnect the connector before starting the next check.
    HINT:
    If the result is as specified, the wire harness between the B ECU and C ECU is functioning normally but the disconnected C ECU is malfunctioning.


A
REPLACE C ECU

B
REPAIR OR REPLACE WIRE HARNESS BETWEEN B ECU AND C ECU

6.CHECK WIRE HARNESS BETWEEN GATEWAY ECU AND A ECU OR C ECU

Lexus Gs430, Gs300. Uzs190 Grs190.Multiplex Communication.Multiplex Communication System. Dtc B1291 Light System Communication Bus Malfunction (+B Short)

  1. Check for a short circuit in B+ or body ground.

    1. Disconnect the A ECU, C ECU and gateway ECU connectors.

    2. Measure the voltage and resistance of the wire harness side connectors.

      Standard voltage:

      Tester Connection
      		Specified Condition
      A ECU connector / Gateway ECU connector - Body ground
      		0 V
      C ECU connector / Gateway ECU connector - Body ground
      		0 V

      Standard resistance:

      Tester Connection
      		Specified Condition
      A ECU connector / Gateway ECU connector - Body ground
      		10 kΩ or higher
      C ECU connector / Gateway ECU connector - Body ground
      		10 kΩ or higher
      HINT:
      1. The A ECU in the door system bus represents the AFS ECU.
      2. The C ECU in the door system bus represents the No. 1 junction block assembly (multiplex network rear ECU).


NG
REPAIR OR REPLACE WIRE HARNESS BETWEEN GATEWAY ECU AND A ECU OR C ECU
OK

REPLACE NETWORK GATEWAY ECU