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Code 1 & Code 2: Oxygen Sensor

  1. Turn off ignition and reset ECU. Remove alternator sense fuse in the under hood relay box for 10 seconds.
  2. Bring engine to operating temperature (cooling fan on). Hold engine at 1500-2000 RPM for 10 minutes, without closing throttle completely during this time. Check if PGM-FI light is on. If not on, test drive and check light again.
  3. If light is on, check fuel pressure at fuel filter. See appropriate FUEL INJECTION article in this section. Repair fuel system if not within specifications. If fuel pressure is within specifications, go to next step.
  4. Disconnect oxygen sensor connector. Attach voltmeter to vehicle ground and connector. With engine at normal operating temperature, open throttle wide open then close throttle.
  5. Voltage at wide open throttle should be above .6 volt and below .4 volt at full closed throttle. If not within specifications, replace oxygen sensor. If voltage is within specifications, go to next step.
  6. Turn engine off and attach system checker harness between ECU and connector. Using a voltmeter, connect negative terminal to connector terminal No. A18.
  7. For front oxygen sensor, attach positive terminal to connector terminal No. C12. Attach to connector terminal No. C10 for rear oxygen sensor. See Figure .
  8. Start engine and warm to operating temperature. Open throttle wide open then close throttle. Voltage at wide open throttle should be above .6 volt and below .4 volt at full closed throttle. If not within specifications, repair wire between ECU and oxygen sensor. If within specifications, go to next step.
  9. Install a known good ECU and recheck system. If failed system is now corrected, replace ECU.
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