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Home >> Acura >> 1989 >> Legend Base, 4D Sedan, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Tests W/Codes - V6 >> Trouble Codes >> Codes 1 & 2 - O2 Sensor >> Oxygen (O2) Sensor

Oxygen (O2) Sensor

  1. Turn ignition off. Remove alternator sense fuse in under-hood relay box for 10 seconds to reset ECU. Start engine. Check fuel pressure. See BASIC TESTING article. Repair fuel system if not within specification. If fuel pressure is within specification, proceed to next step.
  2. Bring engine to operating temperature (cooling fan on). Hold engine speed at 1500 RPM for 15 minutes, without closing throttle completely during this time. Check if "CHECK ENGINE" light is on and if LED is indicating Code 1 or Code 2. If not on, problem is intermittent. Test drive and check again.
  3. If light is on, disconnect indicated oxygen sensor connector. Attach voltmeter to vehicle ground and connector. With engine at normal operating temperature, momentarily open throttle wide open, then close throttle.
  4. Voltage at wide open throttle should be greater than .6 volt, and less than .4 volt at full closed throttle. If not within specification, replace oxygen sensor. If voltage is within specification, proceed to next step.
  5. Turn engine off. Reconnect oxygen sensor connector. Attach ECU test harness between ECU and ECU connector. Restart and warm up engine again. Measure voltage between ECU terminals C12 (pos.) and A18 (neg.) for front oxygen sensor and terminals C10 (pos.) and A18 (neg.) for rear oxygen sensor.
  6. Start engine and warm to operating temperature. Momentarily open throttle wide open, then close throttle. Voltage at wide open throttle should be greater than .6 volt and less than .4 volt at full closed throttle. If not within specification, repair wire between ECU and oxygen sensor. If within specification, substitute a known good ECU. If condition is rectified, replace original ECU.
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