1987 Honda Prelude Si, StandardFACTORY OEM SERVICE PROCEDURE

Cold Engine

  1. Disconnect vacuum hose No. 16 from EGR valve and connect vacuum gauge to hose. Start engine and raise engine speed to 4500-5000 RPM. Vacuum should not be available.
  2. If vacuum is not present, proceed to HOT ENGINE  test. If vacuum is available, check for voltage at EGR control solenoid valve A (Yellow/White wire at emission control box connector).
  3. If voltage is present, replace EGR control solenoid valve A and retest. If there is no voltage, check thermosensor operation, wiring, and fuses and retest. Check thermosensor and vacuum switch C.
  4. Check for voltage at control unit connector (Black/Yellow wire) with ignition on. There should be voltage. If there is no voltage, check wiring. Check Brown/Black wire for continuity between control unit and ground. There should be continuity.
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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