1981 Honda Prelude Automatic TransFACTORY OEM SERVICE PROCEDURE

Accord & Prelude (Man. Trans. Only)

  1. Connect vacuum gauge to vacuum advance hose and start engine. Gauge should show vacuum at 3500 RPM. If vacuum shows on gauge go to step  3). If no vacuum shows on gauge, check for voltage at ignition solenoid valve.
  2. If there is no voltage, check for vacuum at inlet of ignition solenoid valve with engine at 3500 RPM. If there is vacuum, replace ignition solenoid and retest. If there is voltage at ignition solenoid valve, check for vacuum at control switch at idle. If there is no vacuum, replace control switch and retest. If there is vacuum, check for voltage at throttle opener solenoid valve. If no voltage, replace throttle opener solenoid valve. If there is voltage, replace speed sensor and retest.
  3. Jack up front of car and support with safety stands. Push positive probe of voltmeter into Yellow/Green wire connector at control box 2 and connect negative probe to ground.
  4. Start engine and place transmission in second gear. Raise engine speed to 4500 RPM and release throttle suddenly. If voltage appears and vacuum disappears, go on to step  7). If voltage appears and vacuum is still available, replace ignition solenoid valve and retest. If voltage does not appear and vacuum is still available, go to step 5  ).
  5. Check for vacuum at control switch with speed above 15 MPH. If there is vacuum, replace control switch and retest. If there is no vacuum, go to step 6  ).
  6. Check for voltage at throttle opener solenoid valve with speed above 15 MPH. If there is no voltage, replace speed sensor and retest. If there is voltage, check for vacuum at throttle opener solenoid valve. If there is vacuum, replace throttle opener solenoid valve and retest. If there is no vacuum, check for obstruction in vacuum hose.
  7. Attach vacuum pump to vacuum advance diaphragm, start engine and draw 6 in. Hg vacuum. If timing advances, test is complete. If it does not advance, replace vacuum advance diaphragm.
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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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