1979 Honda Prelude Automatic TransFACTORY OEM SERVICE PROCEDURE

1976 Automatic Transmission Equipped Models

  1. Connect a vacuum gauge to hose from retard side of distributor diaphragm. Start engine and check for vacuum (engine cold). There should be no vacuum. If vacuum is present, go to step  4).
  2. Warm engine to normal operating temperature. With engine at idle, there should be no vacuum. If vacuum is present, disconnect thermo sensor and check sensor continuity. If no continuity exists, reconnect sensor and go to next step.
  3. Check voltage at connector Black/Yellow wire. If voltage is present, replace defective vacuum switch. If no voltage is present, check for blocked ignition solenoid valve or blocked vacuum hose. See Figure.
  4. Check voltage at ignition solenoid valve (ignition on). If voltage is present, replace ignition solenoid valve. If no voltage is present, check thermo sensor continuity with coolant temperature below 149°F (65°C). If no continuity exists, replace thermo sensor. If continuity exists, check connections, wiring, or fuse. Repair or replace as necessary.
    Fig 1: 1975 Ignition Timing Control System (Auto. Trans.)
    G09309886Courtesy of AMERICAN HONDA MOTOR CO., INC.
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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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