Heated Steering Wheel (Diagnostics & Symptom Tests): Other Lexus IS III

PRECAUTION [04/2013 - ]

1. PRECAUTION FOR DISCONNECTING CABLE FROM NEGATIVE BATTERY TERMINAL NOTE: When disconnecting the cable from the negative (-) battery terminal, initialize the following systems after the cable is reconnected. System Name See Procedure Variable Gear Ratio Steering System Refer to «INITIALIZATION [04/2013 - ]»(ref-665529-S01115916402014102400000) Air Conditioning System
2. HANDLING PRECAUTIONS FOR SRS AIRBAG SYSTEM This vehicle is equipped with a Supplemental Restraint System (SRS). Failure to carry out service operations in the correct sequence could cause the SRS to unexpectedly deploy during servicing. This may cause a serious accident. Before servicing (including inspection, replacement, removal and installation of parts), be sure to read the precautionary notices for Supplemental Restraint System. Refer to «PRECAUTION [04/2013 - ]»(ref-665792-S23553771532014102400000)

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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 assembly when the steering heater switch (refreshing seat switch) is operated. The heated steering wheel system uses a thermistor inside of the steering wheel assembly to detect the heater temperature and maintain the set temperature. The heated steering wheel timer function 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 (refreshing seat switch) illuminates the LED and current is output from the steering wheel heater control assembly to the steering wheel heater unit of the heated steering wheel system. Pressing the steering heater switch (refreshing seat switch) again turns off the LED and stops the current from being output. A thermostat is installed in the steering wheel heater unit as a safety mechanism. The steering heater switch (refreshing seat switch) LED will go off when either of the following occurs: 1) an open or short in the steering wheel heater unit thermistor continues for 2 seconds or more; or 2) the steering heater switch (refreshing seat switch) is pressed continuously for 10 seconds or more. If the normal condition is restored 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, and regardless of if the normal condition is restored and the system is operating normally, the timer will turn off the heater 30 minutes after the steering heater switch (refreshing seat 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 Operating switch input Input of power circuit latch operation estimate signal LOW / HI input Output LED output Output of LED LOW / HI input Output Heater output Output of heater LOW / HI input Output Latch output Power circuit maintenance LOW / HI input Safety function Content Operation When thermistor malfunction is detected Heater off When overheating (175°C (347°F)) of controller is detected Heater off When load short current (50 A or more) is detected Heater off When undervoltage (4.5 V) is detected Heater off OFF timer (30 min.) After preset time of timer passes, heater off Reverse voltage protection Protection circuit operates

CAUTION / NOTICE / HINT

HINT

Use these procedures to troubleshoot the heated steering wheel system.

PROCEDURE

1. VEHICLE BROUGHT TO WORKSHOP Result Proceed to NEXT Result: 1 NEXT See step 2
2. INSPECT BATTERY VOLTAGE Standard Voltage 11 to 14 V If the voltage is below 11 V, recharge or replace the battery before proceeding to the next step. Result Proceed to NEXT Result: 1 NEXT See step 3
3. PROBLEM SYMPTOMS TABLE Result Result Proceed to Fault is not listed in problem symptoms table A Fault is listed in problem symptoms table B Result: 2 B See step 5 Result: 1 A See step 4
4. OVERALL ANALYSIS AND TROUBLESHOOTING Terminals of ECU Refer to «TERMINALS OF ECU [04/2013 - ]»(ref-665836-S42420275382014102400000) Result Proceed to NEXT Result: 1 NEXT See step 5
5. REPAIR OR REPLACE Result Proceed to NEXT Result: 1 NEXT See step 6
6. CONFIRMATION TEST Result Proceed to NEXT Result: 1 NEXT END

FAIL-SAFE TABLE [04/2013 - ]

1. MALFUNCTION DETECTION Operation when malfunction is detected Content Operation When thermistor malfunction is detected Heater off When overheating (175°C (347°F)) of controller is detected Heater off When load short current (50 A or more) is detected Heater off When undervoltage (4.5 V) is detected Heater off OFF timer (30 min.) After preset time of timer passes, heater off Reverse voltage protection Protection circuit operates Malfunction detection conditions When an open or short in the steering wheel heater unit thermistor continues for 2 seconds or more. When the steering heater switch (refreshing seat switch) is pressed continuously for 10 seconds or more. Malfunction display The LED of the steering heater switch (refreshing seat switch) goes off. Restore condition If the normal condition is restored 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 and regardless of if the normal condition is restored and the system is operating normally, the timer will turn off the heater 30 minutes after the steering heater switch (refreshing seat switch) was first turned on.

HINT

1. Inspect the fuses for circuits related to this system before performing the following inspection procedure.
2. 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.

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1. INSPECT STEERING WHEEL HEATER UNIT (THERMISTOR/HEATER/THERMOSTAT) Disconnect the B steering wheel heater control assembly connector. *a Front view of wire harness connector (to Steering Wheel Heater Control Assembly) Measure the resistance according to the value(s) in the table below. Standard Resistance Tester Connection Condition Specified Condition B-1 (TH1) - B-2 (TH2) 10 to 30°C (50 to 86°F) 8.132 to 18.43 kohms B-4 (SH1) - B-3 (SH2) 20°C (68°F) 1.89 to 2.25 ohms Result Proceed to OK NG Result: 2 NG REPLACE STEERING WHEEL ASSEMBLY. Refer to «REMOVAL [04/2013 - ]»(ref-665793-S14439786512014102400000) Result: 1 OK See step 2
2. INSPECT SPIRAL WITH SENSOR CABLE SUB-ASSEMBLY Check the connectors and cables of the spiral with sensor cable sub-assembly. OK There are no defects such as scratches, cracks, dents or damage on the connectors or cables. Disconnect the K27 and z8 spiral with sensor cable sub-assembly connectors. Measure the resistance according to the value(s) in the table below. *a Component without harness connected (Spiral with Sensor Cable Sub-assembly) Standard Resistance Tester Connection Condition Specified Condition z8-1 (BTM) - K27-1 (BTM) Always 3 ohms or less z8-2 (ETM) - K27-3 (ETM) Always 3 ohms or less z8-3 (EHT) - K27-2 (EHT) Always Below 0.1 ohms z8-4 (BHT) - K27-4 (BHT) Always Below 0.1 ohms Result Proceed to OK NG Result: 2 NG REPLACE SPIRAL WITH SENSOR CABLE SUB-ASSEMBLY. Refer to «REMOVAL [04/2013 - ]»(ref-665530-S18670018912014102400000) Result: 1 OK See step 3
3. CHECK STEERING HEATER SWITCH (REFRESHING SEAT SWITCH) Disconnect the K99 steering heater switch (refreshing seat switch) connector. *a Component without harness connected (Steering Heater Switch (Refreshing Seat Switch)) Measure the resistance according to the value(s) in the table below. Standard Resistance Tester Connection Condition Specified Condition 1 (IG) - 5 (IN) Steering heater switch (refreshing seat switch) is pushed Below 200 ohms 1 (IG) - 5 (IN) Steering heater switch (refreshing seat switch) is not pushed 10 kohms or higher Result Proceed to OK NG Result: 2 NG REPLACE STEERING HEATER SWITCH (REFRESHING SEAT SWITCH). Refer to «REMOVAL [04/2013 - ]»(ref-665743-S32630615382014102400000) Result: 1 OK See step 4
4. CHECK STRG HTR RELAY (STEERING HEATER RELAY) Remove the STRG HTR relay (steering heater relay) from the No. 2 engine room relay block and No. 2 junction block assembly. *1 STRG HTR Relay (Steering Heater Relay) 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 kohms or higher 3 - 5 Voltage is applied between terminals 1 and 2 Below 1 ohms Result Proceed to OK NG Result: 2 NG REPLACE STRG HTR RELAY (STEERING HEATER RELAY) Result: 1 OK See step 5
5. CHECK HARNESS AND CONNECTOR (STEERING HEATER SWITCH (REFRESHING SEAT SWITCH) - SPIRAL WITH SENSOR CABLE SUB-ASSEMBLY) Disconnect the K99 steering heater switch (refreshing seat switch) connector. Disconnect the K27 spiral with sensor cable sub-assembly connector. Measure the resistance according to the value(s) in the table below. Standard Resistance Tester Connection Condition Specified Condition K99-3 (+) - K27-1 (BTM) Always Below 1 ohms K99-5 (IN) - K27-3 (ETM) Always Below 1 ohms K99-3 (+) or K27-1 (BTM) - Body ground Always 10 kohms or higher K99-5 (IN) or K27-3 (ETM) - Body ground Always 10 kohms or higher Result Proceed to OK NG Result: 2 NG REPAIR OR REPLACE HARNESS OR CONNECTOR Result: 1 OK See step 6
6. CHECK HARNESS AND CONNECTOR (STRG HTR RELAY (STEERING HEATER RELAY) - SPIRAL WITH SENSOR CABLE SUB-ASSEMBLY) Remove the STRG HTR relay (steering heater relay) from the No. 2 engine room relay block and No. 2 junction block assembly. Disconnect the K27 spiral with sensor cable sub-assembly connector. Measure the resistance according to the value(s) in the table below. Standard Resistance Tester Connection Condition Specified Condition 5 - K27-4 (BHT) Always Below 1 ohms 5 or K27-4 (BHT) - Body ground Always 10 kohms or higher Result Proceed to OK NG Result: 2 NG REPAIR OR REPLACE HARNESS OR CONNECTOR Result: 1 OK See step 7
7. CHECK HARNESS AND CONNECTOR (STEERING HEATER SWITCH (REFRESHING SEAT SWITCH) POWER SOURCE) Disconnect the K99 steering heater switch (refreshing seat switch) connector. Measure the voltage according to the value(s) in the table below. Standard Voltage Tester Connection Condition Specified Condition K99-1 (IG) - Body ground Engine switch on (IG) 11 to 14 V Result Proceed to OK NG Result: 2 NG REPAIR OR REPLACE HARNESS OR CONNECTOR Result: 1 OK See step 8
8. CHECK HARNESS AND CONNECTOR (STRG HTR RELAY (STEERING HEATER RELAY) POWER SOURCE) Remove the STRG HTR relay (steering heater relay) from the No. 2 engine room relay block and No. 2 junction block assembly. Measure the voltage according to the value(s) in the table below. Standard Voltage Tester Connection Condition Specified Condition 3 - Body ground Always 11 to 14 V 1 - Body ground Engine switch on (IG) 11 to 14 V Measure the resistance according to the value(s) in the table below. Standard Resistance Tester Connection Condition Specified Condition 2 - Body ground Always Below 1 ohms Result Proceed to OK NG Result: 2 NG REPAIR OR REPLACE HARNESS OR CONNECTOR Result: 1 OK See step 9
9. CHECK HARNESS AND CONNECTOR (SPIRAL WITH SENSOR CABLE SUB-ASSEMBLY BODY GROUND) Disconnect the K27 spiral with sensor cable sub-assembly connector. Measure the resistance according to the value(s) in the table below. Standard Resistance Tester Connection Condition Specified Condition K27-2 (EHT) - Body ground Always Below 1 ohms Result Proceed to OK NG Result: 1 OK REPLACE STEERING WHEEL HEATER CONTROL ASSEMBLY. Refer to «REMOVAL [04/2013 - ]»(ref-665793-S36414544772014102400000) Result: 2 NG REPAIR OR REPLACE HARNESS OR CONNECTOR