Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Inspection Procedure
- INSPECT FUSES (DEF, GAUGE, A/C)
- Remove the DEF, GAUGE and A/C fuses from the main body ECU.
- Measure the resistance according to the value(s) in the table below.
Standard resistance
STANDARD RESISTANCE SPECIFICATIONSItem Condition Specified Condition DEF fuse Always Below 1 Ω GAUGE fuse Always Below 1 Ω A/C fuse Always Below 1 Ω - Reinstall the fuses.
NG: REPLACE FUSE
OK: Go to Next Step
- CHECK HARNESS AND CONNECTOR (REAR WINDOW DEFOGGER WIRE BATTERY POSITIVE)
- Measure the voltage according to the value(s) in the table below.
Standard voltage
TESTER CONNECTION AND SPECIFIED CONDITIONTester Connection Switch Condition Specified Condition N2-1 - Body ground Ignition switch ON
Rear defogger switch ON11 to 14 V
NG: Go to step 4
OK: Go to Next Step
- Measure the voltage according to the value(s) in the table below.
- CHECK HARNESS AND CONNECTOR (REAR WINDOW DEFOGGER WIRE CONNECTOR - BODY GROUND)
- Disconnect the O8 rear window defogger wire connector.
- Measure the resistance according to the value(s) in the table below.
Standard resistance
TESTER CONNECTION AND SPECIFIED CONDITIONTester Connection Condition Specified Condition O8-1 - Body ground Always Below 1 Ω - Reconnect the rear window defogger wire connector.
NG: REPAIR OR REPLACE HARNESS OR CONNECTOR
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
OK : REPAIR REAR WINDOW DEFOGGER WIRE (See REPAIR )
- CHECK HARNESS AND CONNECTOR (REAR WINDOW DEFOGGER WIRE - MAIN BODY ECU)
- Disconnect the 4F main body ECU connector.
- Disconnect the N2 rear window defogger wire connector.
- Measure the resistance according to the value(s) in the table below.
Standard resistance
TESTER CONNECTION AND SPECIFIED CONDITIONTester Connection Condition Specified Condition N2-1 - 4F-2 Always Below 1 Ω N2-1 - Body ground Always 10 kΩ or higher - Reconnect the main body ECU connector.
- Reconnect the rear window defogger connector.
NG: REPAIR OR REPLACE HARNESS OR CONNECTOR
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
OK: Go to Next Step
- CHECK HARNESS AND CONNECTOR (REAR WINDOW DEFOGGER SYSTEM POWER SOURCE)
- Disconnect the 4G main body ECU connector.
- Measure the voltage according to the value(s) in the table below.
Standard voltage
TESTER CONNECTION AND SPECIFIED CONDITIONTester Connection Switch Condition Specified Condition 4G-1 - Body ground Ignition switch ON 11 to 14 V - Reconnect the main body ECU connector.
NG: REPAIR OR REPLACE HARNESS OR CONNECTOR
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
OK: Go to Next Step
- INSPECT MAIN BODY ECU (DEF RELAY)
- Remove the main body ECU.
- Remove the GAUGE fuse from the main body ECU.
- Measure the resistance of the DEF relay.
Standard resistance
TESTER CONNECTION AND SPECIFIED CONDITIONTester Connection Condition Specified Condition 4G-1 - 4F-2 When battery voltage absent 10 kΩ or higher 4G-1 - 4F-2 When battery voltage applied to terminals 4Q-12 and GAUGE fuse (DEF relay side) Below 1 Ω - Reinstall the fuse.
- Reinstall the main body ECU.
NG: REPLACE MAIN BODY ECU
OK: Go to Next Step
- CHECK HARNESS AND CONNECTOR (REAR WINDOW DEFOGGER SWITCH - MAIN BODY ECU)
- Disconnect the G6 heater control connector.
- Disconnect the 4Q, 4S main body ECU connector.
- Measure the resistance according to the value(s) in the table below.
Standard resistance
TESTER CONNECTION AND SPECIFIED CONDITIONTester Connection Condition Specified Condition G6-2 (RDEF) - 4Q-12 Always Below 1 Ω G6-3 (IG+) - 4S-10 Always Below 1 Ω G6-2 (RDEF) - Body ground Always 10 kΩ or higher G6-3 (IG+) - Body ground Always 10 kΩ or higher - Reconnect the heater control connector.
- Reconnect the main body ECU connector.
NG: REPAIR OR REPLACE HARNESS OR CONNECTOR
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
OK: Go to Next Step
- CHECK HARNESS AND CONNECTOR (HEATER CONTROL - BODY GROUND)
- Measure the resistance according to the value(s) in the table below.
Standard resistance
TESTER CONNECTION AND SPECIFIED CONDITIONTester Connection Condition Specified Condition G6-1 (E) - Body ground Always Below 1 Ω
NG: REPAIR OR REPLACE HARNESS OR CONNECTOR
OK : REPLACE HEATER CONTROL (See REMOVAL )
- Measure the resistance according to the value(s) in the table below.
Use the Manual With the Right Hardware
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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