1979 Honda Prelude Automatic TransFACTORY OEM SERVICE PROCEDURE

1975 Models

  1. With engine cold, disconnect vacuum hose from distributor diaphragm. SeeΒ Figure and Figure Connect vacuum gauge to vacuum hose and start engine. No vacuum should exist (vacuum should exist on man. trans, equipped models).
  2. If correct vacuum reading is not obtained, check voltage at ignition solenoid valve with ignition on. If voltage is present, solenoid valve is defective or vacuum passage is plugged. Repair or replace as necessary.
  3. If no voltage is present, check thermo sensor continuity with coolant temperature below 149Β°F (65Β°C). If no continuity exists, replace thermo sensor. If continuity exists, check connections, wiring, or fuse. Repair or replace as necessary.
  4. Warm engine to normal operating temperature. Connect vacuum gauge to distributor diaphragm vacuum hose. No vacuum should exist (vacuum should exist on auto, trans, equipped models).
  5. If correct vacuum reading is not obtained, check thermo sensor continuity. If continuity exists, replace defective thermo sensor. If no continuity exists, replace defective ignition solenoid valve.
  6. Increase engine speed to 2000 RPM. Vacuum gauge should indicate vacuum. If not, clean carburetor vacuum port and inspect all vacuum hoses and connections. Repair or replace as necessary.
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:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.

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