Heated Steering Wheel System (Diagnostics & Symptom Tests): Overview Lexus GX J150

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1. SYSTEM DIAGRAM

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1. HEATED STEERING WHEEL SYSTEM The heated steering wheel system heats the steering wheel when the steering heater switch is operated. The heated steering wheel system uses a thermistor inside of the steering wheel to detect the heater temperature and maintain the set temperature. The timer function of the heated steering wheel system turns off the heater after a predetermined period of time.
2. HEATER CONTROLLER SYSTEM Operation description When the engine switch is on (IG), pressing the steering heater switch illuminates the LED and causes current to be output from the steering controller to the heater of the heated steering wheel. Pressing the steering heater switch again turns off the LED and stops the current from being output. A thermostat is installed in the steering wheel as a safety mechanism. The steering heater switch LED will blink at 0.3 second intervals when either of the following occurs: 1) an open or short in the steering wheel thermistor continues for 2 seconds or more; or 2) the steering heater switch is pressed continuously for 10 seconds or more. If the system returns to normal for 2 seconds or more, the previous operation before the malfunction occurred continues. However, regardless of if a malfunction is detected and the malfunction operation is occurring, or if the system returns to normal, the timer will turn off the heater 30 minutes after the switch was first turned on. Signal input/output description Signal Signal Name Function Signal Type Input Thermistor input Input of voltage corresponding to heater temperature Analog input Input Temperature setting input Input of voltage corresponding to temperature setting Analog input Input Switch operation input Input of power circuit's latch operation estimate signal LOW/HI input Output LED output Output to LED LOW/HI input Output Heater output Output to heater LOW/HI input Output Latch output Power circuit maintenance LOW/HI input Safety function Content Operation When thermistor trouble is detected Heater turns off When overheating (150°C (302°F)) of controller is detected Heater turns off When overvoltage (60 V) is detected Heater turns off When undervoltage (6 V) is detected Heater turns off After preset time of timer passes (30 min.) Heater turns off

DESCRIPTION

The heater unit heats the steering wheel when the steering heater switch is operated.

HINT

1. The heater unit is built into the steering wheel.

1. As the steering wheel cannot be disassembled, replace the steering wheel when there is a malfunction in the heater unit.

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1. CHECK STEERING HEATER SWITCH (LED OPERATION) Check the illumination condition of the LED. Result LED Condition Proceed to Blinks Engine switch on (IG) Heated steering wheel switch is pushed and held continuously for 10 seconds or more A Illuminates Engine switch on (IG) Heated steering wheel switch is pushed B Does not blink or illuminate Engine switch on (IG) Heated steering wheel switch is pushed B B --> See step 3 A: Go to next step
2. INSPECT STEERING WHEEL ASSEMBLY (THERMISTOR) Disconnect the steering wheel controller connector. Measure the resistance according to the value(s) in the table below. Standard Resistance Tester Connection Condition Specified Condition 1 (TH2) - 3 (TH1) 25°C (77°F) 9.7 to 10.3 kohms TEXT IN ILLUSTRATION *a Front view of wire harness connector (to Heated Steering Wheel Controller) NG --> See step 7 OK: Go to next step
3. INSPECT STEERING WHEEL ASSEMBLY (HEATER.THERMOSTAT) Disconnect the steering wheel controller connector. Measure the resistance according to the value(s) in the table below. Standard Resistance Tester Connection Condition Specified Condition 2 (SH2) - 4 (SH1) 20°C (68°F) 1.88 to 2.26 ohms TEXT IN ILLUSTRATION *a Front view of wire harness connector (to Heated Steering Wheel Controller) NG --> See step 7 OK: Go to next step
4. CHECK HARNESS AND CONNECTOR (STEERING HEATER SWITCH - SPIRAL CABLE) Disconnect the G66 steering heater switch connector. Disconnect the G30 spiral cable connector. Measure the resistance according to the value(s) in the table below. Standard Resistance Tester Connection Condition Specified Condition G66-5 (INDC) - G30-1 (BTM) Always Below 1 ohms G66-9 (RC) - G30-3 (ETM) Always Below 1 ohms G30-2 (EHT) - Body ground Always Below 1 ohms TEXT IN ILLUSTRATION *a Front view of wire harness connector (to Steering Heater Switch) *b Front view of wire harness connector (to Spiral Cable) Measure the voltage according to the value(s) in the table below. Standard Voltage Tester Connection Switch Condition Specified Condition G30-4 (BHT) - Body ground Engine switch on (IG) 11 to 14 V NG --> REPAIR OR REPLACE WIRE HARNESS OR CONNECTOR OK: Go to next step
5. INSPECT SPIRAL CABLE SUB-ASSEMBLY NOTE: If there are any defects as mentioned below, replace the spiral cable with a new one: Scratches, cracks, dents or chips in the connector or spiral cable. Disconnect the G30 spiral cable connector. Disconnect the heated steering wheel controller connector. Measure the resistance according to the value(s) in the table below. Standard Resistance Tester Connection Condition Specified Condition 1 (CCU) - G30-1 (BTM) Always Below 1 ohms 2 (CCV) - G30-3 (ETM) Always Below 1 ohms 3 (CCX) - G30-2 (EHT) Always Below 1 ohms 4 (CCW) - G30-4 (BHT) Always Below 1 ohms TEXT IN ILLUSTRATION *a Component without harness connected (Spiral Cable) *b Front view of harness connector (to Heated Steering Wheel Controller) NG --> See step 9 OK: Go to next step
6. CHECK STEERING HEATER SWITCH Disconnect the steering heater switch connector. 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 make sure that the polarity is correct. Standard Voltage Tester Connection Positive (+) tester probe - Negative (-) tester probe Switch Condition Specified Condition G66-1 (IG) - G66-4 (RC) Heated steering wheel switch is pushed Below 1.25 V TEXT IN ILLUSTRATION *a Component without harness connected (to Steering Heater Switch) NG --> See step 8 OK --> See step 10
7. REPLACE STEERING WHEEL ASSEMBLY. Refer to «REMOVAL»(ref-524294-S18345652952013012800000)
8. REPLACE STEERING HEATER SWITCH. Refer to «REMOVAL»(ref-524294-S18345652952013012800000)
9. REPLACE SPIRAL CABLE SUB-ASSEMBLY. Refer to «REMOVAL»(ref-524291-S29644211962013012800000)
10. REPLACE HEATED STEERING HEATER CONTROLLER. Refer to «REMOVAL»(ref-524294-S18345652952013012800000)