1990 Lexus ES 250 AutomaticFACTORY OEM SERVICE PROCEDURE

Testing - Preliminary Information

NOTE: Testing individual components does not isolate shorts or opens. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter to isolate wiring harness shorts or opens.
  • NEUTRAL START SWITCH CIRCUIT chart.
  • ECU POWER SOURCE CIRCUIT chart.
  • BACK-UP POWER SOURCE CIRCUIT chart.
  • INJECTOR CIRCUIT chart.
  • COLD START INJECTOR CIRCUIT chart.
  • IDLE SPEED CONTROL (ISC) VALVE CIRCUIT chart.
  • FUEL SYSTEM CIRCUIT chart.
  • FUEL PRESSURE CONTROL VACUUM SWITCHING VALVE (VSV) CIRCUIT chart.
  • TERMINAL TE1 & TE2 CIRCUIT DIAGNOSIS chart.
  • A/C COMPRESSOR CIRCUIT chart.

Refer to the following transmission diagnostic charts:

  • MAIN THROTTLE POSITION SENSOR CIRCUIT chart.
  • NEUTRAL START SWITCH CIRCUIT chart.
  • STOPLIGHT CIRCUIT chart.
  • PATTERN SELECT SWITCH CIRCUIT chart.
  • O/D SWITCH & O/D OFF INDICATOR LIGHT CIRCUIT chart.
  • O/D CANCEL SIGNAL CIRCUIT chart.
  • DIAGNOSIS CIRCUIT chart.
  • CHECK CONNECTOR CIRCUIT chart.
Factory Service Tools

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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.