1987 Honda Prelude Si, StandardFACTORY OEM SERVICE PROCEDURE

Hot Engine

Fig 1: Testing EGR Control Solenoid Valve
G36665
  1. Disconnect vacuum hose from EGR valve and connect vacuum gauge to hose. Connect voltmeter positive probe into the terminal at the control box connector (Yellow/White wire). Connect the negative probe to ground.
  2. Start and warm-up engine to normal operating temperature (cooling fan must come on). Test EGR system under the following engine operating conditions. Check vacuum and voltage specifications.
    EGR SYSTEM TEST

    Engine Condition EGR Valve Vacuum Yellow/White Wire Voltage
    1 Idle None Yes
    2 Hard Accel. 2-6 in. Hg None
    3 4500 RPM 2-6 in. Hg None
    4 Deceleration None Yes
  3. If vacuum is present in condition No. 1 or no vacuum available for condition No. 2 and No. 3, check vacuum hose routing. If there are no defects, replace the EGR control valves A and B.
  4. If no voltage is present for condition No. 1 or No. 4, or there is voltage for condition No. 2 or No. 3, check thermosensor and vacuum switch C. Check for voltage at control unit connector (Black/Yellow wire) with ignition on. There should be voltage. If there is no voltage, check wiring.
  5. Check Brown/Black wire for continuity between control unit and ground. Wire should have continuity. If vacuum is available for condition No. 4, replace EGR solenoid valve A. Retest system.
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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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