1991 Acura Legend Base, AutomaticFACTORY OEM SERVICE PROCEDURE

Code 4: Crank/CYL Sensor

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. Start engine, and connect jumper wire to diagnostic connector. Observe CHECK ENGINE light. If light is not flashing, problem is intermittent. Check for poor and loose connections at CRANK/CYL sensor connector, connector C353 at right shock tower and at ECU. Test drive, and check again.
  2. If CHECK ENGINE light is flashing Code 4, turn ignition off. Disconnect 8-pin CRANK/CYL sensor connector nearest sensor. Measure resistance across Pink and Gray terminals at sensor. See Fig 1 . If reading is not 650-900 ohms, replace sensor. If reading is within specification, go to next step.
    Fig 1: Identifying CRANK/CYL Sensor Connector
    G91J16286Courtesy of AMERICAN HONDA MOTOR CO., INC.
  3. Check continuity between ground and sensor Pink wire terminal. Check continuity between ground and sensor Gray terminal. If continuity exists, sensor is shorted to ground. Replace sensor. If no continuity exists, go to next step.
  4. Reconnect sensor connector. Attach ECU test harness to main wire harness side only. Measure resistance between harness terminals B15 and B16. See Figure . Resistance should be 650-900 ohms.
  5. If resistance is not within specification, repair open in Pink and/or Gray wire. If resistance is within specification, check continuity of harness terminal B15 to ground. If continuity is not present, substitute a known good ECU. If condition goes away, replace ECU.
  6. If continuity is present, repair short to ground in Gray wire between harness terminal B15 and 8-pin CRANK/CYL sensor connector.
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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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