1991 Acura Legend Base, AutomaticFACTORY OEM SERVICE PROCEDURE

Code 18: Ignition Timing Adjuster

NOTE: For wiring diagrams, see WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section. For vacuum diagrams, see VACUUM DIAGRAMS article in the ENGINE PERFORMANCE Section.
  1. Turn ignition off. Remove ACG fuse in underdash fuse box for 10 seconds to reset ECU. Turn ignition on, and connect jumper wire to diagnostic connector. Check if CHECK ENGINE light flashes. If light does not flash, problem is intermittent. Check for poor connections and loose wires at ignition timing adjuster connector.
  2. If CHECK ENGINE light flashes Code 18, turn ignition off. Disconnect ignition timing adjuster 3-pin connector at right side of firewall. See Fig 1 . Measure resistance between "A" and "C" terminals of ignition timing adjuster.
    Fig 1: Identifying Ignition Timing Adjuster Connector
    G91F16290Courtesy of AMERICAN HONDA MOTOR CO., INC.
  3. Resistance should be 3500-6500 ohms. If resistance is as specified, go to next step. If resistance is not 3500-6500 ohms, replace ignition timing adjuster.
  4. If resistance is within specification, measure and record resistance between "A" and "B" terminals on timing adjuster side of harness. Measure and record resistance between "B" and "C" terminals on same side of connector. Add both resistance values together. If total of resistance values is not 3000-6000 ohms, replace ignition timing adjuster.
  5. If resistance is 3000-6000 ohms, turn ignition on. Measure voltage between Yellow/White (positive) and Green/White (negative) wire terminals on harness side of connector. If voltage is about 5 volts, go to step 8).
  6. If voltage reading is not about 5 volts, measure voltage between ground and Yellow/White wire terminal. If voltage reading is about 5 volts, repair open in Green/White wire between ECU terminal D22 and ignition timing adjuster connector.
  7. If voltage is not 5 volts, turn ignition off. Connect ECU test harness between ECU and ECU connector. Turn ignition on. Measure voltage between ECU terminals D20 (positive) and D22 (negative). See Figure . If about 5 volts are present, repair open in Yellow/White wire between ECU terminal D20 and ignition timing adjuster. If about 5 volts are not present, substitute a known good ECU, and recheck. If specified voltage is now available, replace ECU.
  8. If voltage reading between Yellow/White and Green/White (negative) wire terminals in step 5) was about 5 volts, turn ignition off. Reconnect ignition timing adjuster connector. Connect ECU test harness between ECU and ECU connector.
  9. Turn ignition on. Measure voltage between ECU terminals D8 (positive) and D22 (negative). If voltage is not .5-4.5 volts, repair open or short in Blue/Yellow wire between ECU terminal D8 and ignition timing adjuster.
  10. If voltage reads .5-4.5 volts, substitute a known good ECU, and recheck. If condition goes away, replace ECU.
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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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