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Home >> Acura >> 1990 >> Legend Base, 4D Sedan, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Code 4: Crank/CYL Sensor
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Code 4: Crank/CYL Sensor

NOTE: For wiring diagrams, see WIRING DIAGRAMS article. For vacuum diagrams, see VACUUM DIAGRAMS article.
  1. Turn ignition off. Disconnect alternator sense fuse in under-hood relay box for 10 seconds to reset ECU. Start engine and observe CHECK ENGINE and LED lights. If light are off, problem is intermittent. Check for poor or loose connections at CRANK/CYL sensor connector, connectors C102 and C305 at right shock tower. Test drive and check again.
  2. If CHECK ENGINE light is on and LED indicates Code 4, turn ignition off. Disconnect CRANK/CYL sensor connector nearest the sensor. Measure resistance across Blue/Yellow and Blue/Green terminals at sensor. If reading is not 500-1000 ohms, replace sensor. If reading is within specification, proceed to step 3).
  3. Check continuity between ground and sensor Blue/Yellow wire terminal. Check continuity between ground and sensor Blue/Green terminal. If continuity exists, sensor is shorted to ground. Replace sensor. If no continuity exists, proceed to step 4).
  4. Reconnect sensor connector. Attach ECU test harness to main wire harness side only. Measure resistance between ECU terminals B19 and B20. See Figure . Resistance should be 500-1000 ohms.
  5. If resistance is not within specification, repair open in Blue/Yellow and/or Blue/Green wire. If resistance is within specification, check continuity of ECU terminal B19 to ground. If continuity is not present, substitute a known good ECU. If condition goes, replace original ECU.
  6. If continuity is present, repair short to ground in Blue/Green wire between ECU terminal B19 and 4-pin CRANK/CYL sensor connector.
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