Lexus IS250 · Service Manual BODY

Driver Side ECU Power Source Circuit

Circuit diagnosis

DESCRIPTION

The driver side position control ECU is contained in the driver side front power seat switch.
During manual operation, only one switch signal is accepted. If signals are input from 2 or more switches simultaneously, all of them are ignored, except when signals are input from the front vertical switch and lifter switch simultaneously. In this case, the signal from the lifter switch will operate.
During automatic operation, a manual switch input will override any other operations, i.e. automatic operations will stop and the manual input operation only will be accepted. For example, if a manual switch input is activated during a seat store/restore operation, the previous operation will cease and manual operation will be performed. After the manual operation is performed, the previous automatic operation will not resume.
The power mirror store/restore operation is unaffected by manual switch inputs.
The front power seat switch does not allow the restore operation of the power seat when the system detects that the voltage of terminal SYSB is less than 8.0 +- 0.5 V for 30 msec. or is more than 10 +- 0.5 V for 30 msec.
This circuit is the power source circuit for the driver side front power seat switch (position control ECU).

HINT:
  1. Manual adjustment of the slide, reclining, or lumbar can be performed even when the driver side front power seat switch is not functional if current is allowed to flow into terminals +B and SYSB.

Lumbar support operation can be performed at all times.

WIRING DIAGRAM

B126232E02
B126233E02

INSPECTION PROCEDURE


1. INSPECT FRONT POWER SEAT SWITCH (POSITION CONTROL ECU POWER SOURCE CIRCUIT)

  1. B128716E02
    LHD

    1. Disconnect the front power seat switch LH (position control ECU) connectors.

    2. Measure the voltage according to the value(s) in the table below.

      Standard voltage:
      Tester Connection
      		 Condition
      		 Specified Condition
      U6-5 (+B) - Body ground
      		 Always
      		 10 to 14 V
      U7-4 (IG) - Body ground
      		 Engine switch on (IG)
      		 10 to 14 V
      U7-8 (SYSB) - Body ground
      		 Always
      		 10 to 14 V

  1. B128716E03
    RHD

    1. Disconnect the front power seat switch RH (position control ECU) connectors.

    2. Measure the voltage according to the value(s) in the table below.

      Standard voltage:
      Tester Connection
      		 Condition
      		 Specified Condition
      T6-5 (+B) - Body ground
      		 Always
      		 10 to 14 V
      T7-4 (IG) - Body ground
      		 Engine switch on (IG)
      		 10 to 14 V
      T7-8 (SYSB) - Body ground
      		 Always
      		 10 to 14 V



NG
REPAIR OR REPLACE HARNESS OR CONNECTOR (POWER SOURCE CIRCUIT)
OK


2. INSPECT FRONT POWER SEAT SWITCH (POSITION CONTROL ECU GROUND CIRCUIT)

  1. B085084E08
    LHD

    1. Measure the resistance according to the value(s) in the table below.

      Standard resistance:
      Tester Connection
      		 Condition
      		 Specified Condition
      U6-1 (GND) - Body ground
      		 Always
      		 Below 1 Ω

  1. B085084E07
    RHD

    1. Measure the resistance according to the value(s) in the table below.

      Standard resistance:
      Tester Connection
      		 Condition
      		 Specified Condition
      T6-1 (GND) - Body ground
      		 Always
      		 Below 1 Ω



NG
REPAIR OR REPLACE HARNESS OR CONNECTOR (GROUND CIRCUIT)
OK

PROCEED TO NEXT CIRCUIT INSPECTION SHOWN IN PROBLEM SYMPTOMS TABLE


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