1990 Toyota Corolla Base, AutomaticFACTORY OEM SERVICE PROCEDURE

Sub-Oxygen Sensor Test

  1. Inspection is required when trouble code No. 27 exists. Clear trouble codes. See CLEARING TROUBLE CODES under TESTS W/CODES article in this section. Warm engine to normal operating temperature.
    CAUTION: DO NOT  exceed 62 MPH or trouble code will be cancelled.
  2. Drive vehicle between 50 and 61 MPH for at least 5 minutes in 4th or 5th gear (Man. Trans.) or "D" range (Auto. Trans.).
  3. Fully depress accelerator pedal for at least 10 seconds with engine RPM at least 3000 RPM.
  4. Stop engine and turn ignition off. Repeat previous steps and note if trouble code No. 27 exists again. If trouble code exists again, check sub-oxygen sensor circuit for continuity, shorts or grounds. Replace sub-oxygen sensor if circuit is okay.
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.

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