Lexus RX (RX 350L, RX450h) 2016-2026 Repair Manual: Linear Solenoid Power Supply System Malfunction (C120C)

Lexus RX (RX 350L, RX450h) 2016-2026 Repair Manual / Drivetrain / Mf1a (transfer / 4wd / Awd) / Dynamic Torque Control Awd System / Linear Solenoid Power Supply System Malfunction (C120C)

DESCRIPTION

This DTC is output by the 4WD ECU assembly if a malfunction occurs in the linear solenoid power supply system.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

C120C

Linear Solenoid Power Supply System Malfunction
  • When the 4WD relay is operating, the 4WD relay monitor remains off for 1 second or more while the voltage at the IG1 terminal is 9.5 V or more
  • When the 4WD relay is operating, the 4WD relay monitor remains off for 1 second or more while the voltage at the IG1 terminal is less than 9.5 V
  • While the 4WD relay is not operating, the 4WD relay monitor remains on for 1 second or more after the engine switch is turned on (IG)
  • Wire harness and connector (IG1 circuit, GND circuit)
  • 4WD ECU assembly

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

  • Inspect the fuses for circuits related to this system before performing the following inspection procedure.
  • When the 4WD ECU assembly is replaced with a known good one from another vehicle, it is necessary to perform calibration.

    Click here

HINT:

Check the condition of each related circuit connector before troubleshooting.

Click here

PROCEDURE

1.

CHECK HARNESS AND CONNECTOR (IG1 TERMINAL)

(a) Disconnect the R10 4WD ECU assembly connector.

(b) Turn the engine switch on (IG).

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

Standard Voltage:

Tester Connection

Switch Condition

Specified Condition

R10-3 (IG1) -Body ground

Engine switch on (IG)

11 to 14 V
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

2.

CHECK HARNESS AND CONNECTOR (GND TERMINAL)

(a) Turn the engine switch off.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

R10-4 (GND) -Body ground

Always

Below 1 Ω
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

3.

RECONFIRM DTC

(a) Connect the R10 4WD ECU assembly connector.

(b) Clear the DTCs.

Click here

Chassis > Four Wheel Drive > Clear DTCs

(c) Turn the engine switch off.

(d) Turn the engine switch on (IG).

(e) Check that no DTCs other than DTC C120C are output.

Click here

Chassis > Four Wheel Drive > Trouble Codes

Result

Proceed to

DTCs other than C120C are not output

A

DTCs other than C120C are output

B
A

REPLACE 4WD ECU ASSEMBLY

B

REPAIR CIRCUIT INDICATED BY OUTPUT CODE

    Fail-safe Chart
    FAIL-SAFE CHART FAIL-SAFE FUNCTION If a malfunction is detected in the 4WD ECU assembly, the 4WD ECU assembly may stop AWD control and transfer all torque to the front wheels, or function in a such ...

    Low or High Power Supply Voltage (C1241)
    DESCRIPTION If a malfunction in the power source circuit occurs, or a communication malfunction with the skid control ECU (brake actuator assembly) or speed sensor occurs, the 4WD ECU assembly prohibi ...

    Other materials:

    Lexus RX (RX 350L, RX450h) 2016-2026 Repair Manual > Lighting System (w/ Automatic Headlight Beam Level Control System): Left Headlight ECU Variation Error (B2456)
    DESCRIPTION This DTC is stored if the No. 1 headlight ECU sub-assembly LH for another destination is installed. DTC No. Detection Item DTC Detection Condition Trouble Area DTC Output from B2456 Left Headlight ECU Variation Error The engine switch is on (IG). Vehicle speci ...

    Lexus RX (RX 350L, RX450h) 2016-2026 Repair Manual > Navigation System: Extension Module Malfunction 2 (B1556)
    DESCRIPTION This DTC is stored when a malfunction occurs in the Navigation ECU. DTC No. Detection Item DTC Detection Condition Trouble Area B1556 Extension Module Malfunction 2 When any of the following conditions is met: Internal power supply malfunction Internal hard drive ma ...

    Lexus RX (RX 350L, RX450h) 2016-{YEAR} Owners Manual

    Lexus RX (RX 350L, RX450h) 2016-{YEAR} Repair Manual

    © 2026 Copyright www.lexusrx.net
    0.0086