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.
Section 993 (Overhead Junction Block): Inspection
- INSPECT OVERHEAD JUNCTION BLOCK ASSEMBLY
Disconnect the connector from the overhead J/B and inspect the connector on the wire harness side, as shown.
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
CONNECTOR TERMINALS SPECIFIED CONDITIONTester connection Condition Specified condition 1 - Ground Constant Continuity 5 - Ground Constant Continuity 13 - Ground Constant Battery positive voltage 17 - Ground Constant Battery positive voltage 26 - Ground Ignition switch OFF or ACC No voltage Ignition switch ON Battery positive voltage If continuity is not as specified, replace the overhead junction block.
- Overhead J/B side: INSPECT OVERHEAD JUNCTION BLOCK ASSEMBLY
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
CONNECTOR TERMINALS SPECIFIED CONDITIONCircuit name Tester connection Specified condition Power source circuit A12-A26-A27-A28 Continuity Power source circuit A13-C6-D6 Continuity Multiplex communication circuit A14-A30-A31 Continuity Ground circuit A1-A15-A16-A32-C8-D2-E4-Body ground Continuity Microphone circuit B1-A19 Continuity Microphone circuit B4-A2 Continuity Microphone circuit B5-A3 Continuity Microphone circuit B6-A18 Continuity Mayday switch circuit D1-A23 Continuity Mayday switch circuit D3-A22 Continuity Mayday switch circuit D5-A21 Continuity Rader sensor circuit E1-A7 Continuity Rader sensor circuit E2-A8 Continuity Rader sensor circuit E3-A9 Continuity If continuity is not as specified, replace the overhead J/B assembly.
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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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