Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Steering Wheel does not Heat Up When Heated Steering Wheel Switch is Pressed

Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual / Suspension / Steering Column / Heated Steering Wheel System / Steering Wheel does not Heat Up When Heated Steering Wheel Switch is Pressed

DESCRIPTION

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WIRING DIAGRAM

CAUTION / NOTICE / HINT

HINT:

  • Inspect the fuses for circuits related to this system before performing the following inspection procedure.
  • The steering wheel heater unit is built into the steering wheel assembly which cannot be disassembled. Therefore, when the steering wheel heater unit has a malfunction, replace the steering wheel assembly.

PROCEDURE

1.

CHECK IG1-MAIN RELAY

(a) Remove the IG1-MAIN relay from the engine room relay block.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

3 - 5

Voltage is not applied between terminals 1 and 2

10 kΩ or higher

Voltage is applied between terminals 1 and 2

Below 1 Ω

*1

IG1-MAIN Relay
NG

REPLACE IG1-MAIN RELAY
OK

2.

CHECK HARNESS AND CONNECTOR (IG1-MAIN RELAY POWER SOURCE)

(a) Remove the IG1-MAIN relay from the engine room relay block.

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

Standard Voltage:

Tester Connection

Condition

Specified Condition

5 (IG1-MAIN relay) - Body ground

Always

11 to 14 V

1 (IG1-MAIN relay) - Body ground

Engine switch on (IG)

11 to 14 V

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

2 (IG1-MAIN relay) - Body ground

Always

Below 1 Ω
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

3.

CHECK HARNESS AND CONNECTOR (STEERING HEATER SWITCH (INTEGRATION CONTROL AND PANEL ASSEMBLY) POWER SOURCE)

(a) Disconnect the J84 steering heater switch (integration control and panel assembly) connector.

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

Standard Voltage:

Tester Connection

Condition

Specified Condition

J84-4 (IG1) - Body ground

Engine switch on (IG)

11 to 14 V
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

4.

CHECK STEERING HEATER SWITCH (INTEGRATION CONTROL AND PANEL ASSEMBLY)

(a) Disconnect the J84 steering heater switch (integration control and panel assembly) connector.

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

HINT:

As the circuit has a diode, perform the measurement in diode test mode, and do not mistake the polarity.

Standard Voltage:

Tester Connection(Positive (+) tester probe - Negative (-) tester probe)

Condition

Specified Condition

J84-4 (IG1) - J84-9 (IND)

Always

Below 1.25 V

J84-16 (ECU) - J84-9 (IND)

Steering heater switch (Integration control and panel assembly) is pushed

Below 1.25 V

*a

Component without harness connected

(Steering Heater Switch (Integration Control and Panel Assembly))

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

J84-4 (IG1) - J84-16 (ECU)

Steering heater switch (Integration control and panel assembly) is pushed

Below 1 Ω

Steering heater switch (Integration control and panel assembly) is not pushed

10 kΩ or higher
NG

REPLACE STEERING HEATER SWITCH (INTEGRATION CONTROL AND PANEL ASSEMBLY)

OK

5.

CHECK HARNESS AND CONNECTOR (IG1-MAIN RELAY - SPIRAL CABLE SUB-ASSEMBLY)

(a) Remove the IG1-MAIN relay from the engine room relay block.

(b) Disconnect the J23 spiral cable sub-assembly connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

3 (IG1-MAIN Relay) - J23-4 (BHT)

Always

Below 1 Ω

3 (IG1-MAIN Relay) or J23-4 (BHT) - Body ground

Always

10 kΩ or higher
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

6.

CHECK HARNESS AND CONNECTOR (STEERING HEATER SWITCH (INTEGRATION CONTROL AND PANEL ASSEMBLY) - SPIRAL CABLE SUB-ASSEMBLY)

(a) Disconnect the J84 steering heater switch (integration control and panel assembly) connector.

(b) Disconnect the J23 spiral cable sub-assembly connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

J84-9 (IND) - J23-1 (BTM)

Always

Below 1 Ω

J84-16 (ECU) - J23-3 (ETM)

Always

Below 1 Ω

J84-9 (IND) or J23-1 (BTM) - Body ground

Always

10 kΩ or higher

J84-16 (ECU) or J23-3 (ETM) - Body ground

Always

10 kΩ or higher
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

7.

INSPECT SPIRAL CABLE SUB-ASSEMBLY

(a) Check the connectors and cables of the spiral cable sub-assembly .

OK:

There are no defects such as scratches, cracks, dents or damage on the connectors or cables.

(b) Disconnect the J23 and z11 spiral cable sub-assembly connectors.

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

*a

Component without harness connected

(Spiral Cable Sub-assembly)

-

-

Standard Resistance:

Tester Connection

Condition

Specified Condition

z11-2 (BTM) - J23-1 (BTM)

Always

3 Ω or less

z11-3 (ETM) - J23-3 (ETM)

Always

3 Ω or less

z11-1 (EHT) - J23-2 (EHT)

Always

Below 0.1 Ω

z11-4 (BHT) - J23-4 (BHT)

Always

Below 0.1 Ω
NG

REPLACE SPIRAL CABLE SUB-ASSEMBLY

OK

8.

CHECK HARNESS AND CONNECTOR (SPIRAL CABLE SUB-ASSEMBLY BODY GROUND)

(a) Disconnect the J23 spiral cable sub-assembly connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

J23-2 (EHT) - Body ground

Always

Below 1 Ω
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

9.

INSPECT STEERING WHEEL HEATER UNIT (THERMISTOR/HEATER/THERMOSTAT)

(a) Disconnect the B steering vibration and heater ECU connector.

*a

Front view of wire harness connector

(to Steering Vibration and Heater ECU)

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

B-3 (TH1) - B-2 (TH2)

10 to 30°C (50 to 86°F)

4.228 to 8.701 kΩ

B-5 (SH1) - B-1 (SH2)

20°C (68°F)

2.43 to 2.89 Ω
OK

REPLACE STEERING VIBRATION AND HEATER ECU

NG

REPLACE STEERING WHEEL ASSEMBLY

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