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Code 1/Code 2 O2 Sensor

  1. Turn off ignition. Reset ECU by removing clock fuse in the under-hood relay box for 10 seconds. Start engine. Check fuel pressure at fuel filter. See appropriate FUEL INJECTION article in FUEL SYSTEMS section. Repair fuel system if not within specifications. If fuel pressure is within specifications, proceed to next step.
  2. Bring engine to operating temperature (cooling fan comes on). Hold engine speed at 1500 RPM (minimum) for 15 minutes, without closing throttle completely during this time. Check if PGM-FI or Check Engine Warning Light is on. If not on, problem is intermittent. Test drive and check light again.
  3. If light is on, disconnect indicated oxygen sensor connector. Attach voltmeter to vehicle ground and oxygen sensor 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 closed throttle. If not within specifications, replace oxygen sensor. If voltage is within specifications, proceed to next step.
  5. Turn engine off and attach system checker harness between ECU and ECU connector. Using a voltmeter, connect negative lead to connector terminal A18.
  6. On Prelude models, for oxygen sensor A, attach positive voltmeter lead to connector terminal C16 and attach to connector terminal B11 for oxygen sensor B.
  7. 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 closed throttle. If not within specifications, repair wire between ECU and oxygen sensor. If within specifications, substitute a known good ECU. If condition is rectified, replace original ECU.
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