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.
System Diagnosis
ECT ECU monitors engine and transmission operation and contains a self-diagnostic system which stores DTCs. A Malfunction Indicator Light (MIL), also called CHECK ENGINE light, located on instrument panel, will illuminate if a system or component fails and sets a DTC.
MIL illuminates with ignition switch in ON position, engine off (KOEO). Once engine is started, MIL should go out. If MIL remains illuminated, ECT ECU has detected a malfunction or abnormality in system. If MIL does not illuminate, inspect circuit and light. See WIRING DIAGRAMS .
If malfunction does not reoccur in 3 trips, MIL goes off, but Diagnostic Trouble Code (DTC) remains recorded in ECT ECU memory. Trouble codes may only be retrieved using an appropriate scan tool or Lexus/Toyota scan tool connected to 16-pin Data Link Connector (DLC-3), located at lower left corner of instrument panel or below parking brake handle. See Figure and Figure . Scan tool also provides freeze-frame data and can be used to clear trouble codes.
ECT ECU records engine operating condition (fuel system, calculated load, coolant temperature, fuel trim (mixture), engine speed, vehicle speed, etc.) with 1st malfunction ONLY. Information is ONLY for 1st recorded failure, even if more than one code has been recorded. Freeze-frame data is only updated when all trouble codes have been cleared, or a misfire or fuel-trim malfunction has occurred.
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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.